=head1 名前

guestfs - 仮想マシンイメージのアクセスまたは変更のためのライブラリ

=head1 書式

#include <guestfs.h>
 guestfs_h *g = guestfs_create ();
 guestfs_add_drive (g, "guest.img");
 guestfs_launch (g);
 guestfs_mount (g, "/dev/sda1", "/");
 guestfs_touch (g, "/hello");
 guestfs_umount (g, "/");
 guestfs_shutdown (g);
 guestfs_close (g);

 cc prog.c -o prog -lguestfs
or:
 cc prog.c -o prog `pkg-config libguestfs --cflags --libs`

=head1 説明

Libguestfs is a library for accessing and modifying disk images and virtual
machines.

This manual page documents the C API.

If you are looking for an introduction to libguestfs, see the web site:
L<http://libguestfs.org/>

Each virt tool has its own man page (for a full list, go to L</SEE ALSO> at
the end of this file).

Other libguestfs manual pages:

=over 4

=item L<guestfs-faq(1)>

Frequently Asked Questions (FAQ).

=item L<guestfs-examples(3)>

Examples of using the API from C.  For examples in other languages, see
L</USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES> below.

=item L<guestfs-recipes(1)>

Tips and recipes.

=item L<guestfs-performance(1)>

Performance tips and solutions.

=item L<libguestfs-test-tool(1)>

=item L<guestfs-testing(1)>

Help testing libguestfs.

=item L<guestfs-building(1)>

How to build libguestfs from source.

=item L<guestfs-hacking(1)>

Contribute code to libguestfs.

=item L<guestfs-internals(1)>

How libguestfs works.

=item L<guestfs-security(1)>

Security information, including CVEs affecting libguestfs.

=back

=head1 API 概要

このセクションは libguestfs API の簡単な概要を示します。  一緒に呼ばれるグループ API
を試みます。これは、このマニュアルのメインセクションにおいて個々の呼び出しに関して読む必要が無くなります。

=head2 ハンドル

libguestfs 呼び出しを使用する前に、ハンドルを作成する必要があります。そして、少なくとも 1
つのディスクイメージをハンドルを追加する必要があります。続けて、ハンドルを開始して、好きな操作を実行します。最後に、ハンドルを閉じます。利便性のため、ハンドル変数の名前を
1 文字の C<g> を使用します。もちろん、好きな名前を使うことができます。

libguestfs を使用しているすべてのプログラムの一般的な構造はこのようなものです:

 guestfs_h *g = guestfs_create ();
 
 /* 複数のディスクイメージがあれば、その回数だけ
  * guestfs_add_drive を呼び出します。
  */
 guestfs_add_drive (g, "guest.img");
 
 /* 大抵の操作呼び出しはハンドル 'g' を開始するまでうまく
  * 機能しません。ドライブを追加した「後」、他のコマンド
  * を実行する「前」にこれを行う必要があります。
  */
 guestfs_launch (g);
 
 /* Either: examine what partitions, LVs etc are available: */
 char **partitions = guestfs_list_partitions (g);
 char **logvols = guestfs_lvs (g);
 
 /* Or: ask libguestfs to find filesystems for you: */
 char **filesystems = guestfs_list_filesystems (g);
 
 /* Or: use inspection (see INSPECTION section below). */
 
 /* To access a filesystem in the image, you must mount it. */
 guestfs_mount (g, "/dev/sda1", "/");
 
 /* これで、仮想マシンのイメージにおいて、ファイルシステムの
  * アクションを実行できます。
  */
 guestfs_touch (g, "/hello");
 
 /* ディスクを同期します。これは guestfs_launch の反対です。 */
 guestfs_shutdown (g);
 
 /* ハンドル 'g' を閉じて開放します。 */
 guestfs_close (g);

The code above doesn't include any error checking.  In real code you should
check return values carefully for errors.  In general all functions that
return integers return C<-1> on error, and all functions that return
pointers return C<NULL> on error.  See section L</ERROR HANDLING> below for
how to handle errors, and consult the documentation for each function call
below to see precisely how they return error indications.

The code above does not L<free(3)> the strings and arrays returned from
functions.  Consult the documentation for each function to find out how to
free the return value.

See L<guestfs-examples(3)> for fully worked examples.

=head2 ディスクイメージ

イメージファイル名 (上の例では C<"guest.img">) は、仮想マシンのディスクイメージ、物理ハードディスクの L<dd(1)>
コピー、実際のブロックデバイス、単に L<posix_fallocate(3)> から作成した 0 の空ファイルがありえます。libguestfs
はこれらすべてに役に立つことをさせます。

近代的なコードにおいてドライブを追加するために使用する呼び出しは L</guestfs_add_drive_opts> です。書き込み許可、raw
形式指定にて、ディスクイメージを追加するには、次を実行します:

 guestfs_add_drive_opts (g, filename,
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         -1);

以下を使用して、読み込み専用のディスクを追加できます:

 guestfs_add_drive_opts (g, filename,
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
                         -1);

or by calling the older function L</guestfs_add_drive_ro>.  If you use the
readonly flag, libguestfs won't modify the file.  (See also L</DISK IMAGE
FORMATS> below).

ディスクイメージが使用中ならば、たとえば仮想マシンにより使用されているならば、特に注意してください。読み書き可能で追加することにより、ほぼ確実にディスク破損を引き起こします。一方、読み込み専用で追加することは安全です。

You should usually add at least one disk image, and you may add multiple
disk images.  If adding multiple disk images, they usually have to be
"related", ie. from the same guest.  In the API, the disk images are usually
referred to as F</dev/sda> (for the first one you added), F</dev/sdb> (for
the second one you added), etc.

一度 L</guestfs_launch>
が呼び出されると、これ以上イメージを追加することはできません。それらを追加するためには、デバイス名の一覧を取得するために
L</guestfs_list_devices> を呼び出せます。以下の L</ブロックデバイス命名法> を参照してください。

There are slightly different rules when hotplugging disks (in libguestfs
E<ge> 1.20).  See L</HOTPLUGGING> below.

=head2 マウント

Before you can read or write files, create directories and so on in a disk
image that contains filesystems, you have to mount those filesystems using
L</guestfs_mount> or L</guestfs_mount_ro>.  If you already know that a disk
image contains (for example) one partition with a filesystem on that
partition, then you can mount it directly:

 guestfs_mount (g, "/dev/sda1", "/");

where F</dev/sda1> means literally the first partition (C<1>) of the first
disk image that we added (F</dev/sda>).  If the disk contains Linux LVM2
logical volumes you could refer to those instead (eg. F</dev/VG/LV>).  Note
that these are libguestfs virtual devices, and are nothing to do with host
devices.

If you are given a disk image and you don’t know what it contains then you
have to find out.  Libguestfs can do that too: use
L</guestfs_list_partitions> and L</guestfs_lvs> to list possible partitions
and LVs, and either try mounting each to see what is mountable, or else
examine them with L</guestfs_vfs_type> or L</guestfs_file>.  To list just
filesystems, use L</guestfs_list_filesystems>.

Libguestfs also has a set of APIs for inspection of unknown disk images (see
L</INSPECTION> below).  You might also want to look at higher level programs
built on top of libguestfs, in particular L<virt-inspector(1)>.

ファイルシステムを読み込み専用でマウントするには L</guestfs_mount_ro> を使用します。いくつかの他の変種
C<guestfs_mount_*> 呼び出しがあります。

=head2 ファイルシステムのアクセスおよび変更

libguestfs API
の大半は、マウントされたファイルシステムにあるファイル、ディレクトリー、シンボリックリンクなどを参照および変更するためのかなり低レベルな関数呼び出しから構成されます。このマニュアルページにおいて以下に詳細に一覧化されている、そのような呼び出しは
100 以上あります。この概要においてすべてを取り扱うことは考えていません。

C<"/"> から始まり、マウントポイントを含む完全パスとしてファイル名を指定します。

たとえば、C<"/"> にファイルシステムをマウントして、C<"etc/passwd"> というファイルを読み込みたければ、次のようにできます:

 char *data = guestfs_cat (g, "/etc/passwd");

これは、ファイルの完全な内容を含む（いくつかの条件とともに: 以下の L</ダウンロード> 参照）新しく割り当てられたバッファーとして C<data>
を返します。もしくは、エラーがあれば C<NULL> を返します。

もう 1 つの例として、ファイルシステムに C<"var"> という名前の最上位ディレクトリーを作成するには、次のようにします:

 guestfs_mkdir (g, "/var");

シンボリックリンクを作成するには次のようにできます:

 guestfs_ln_s (g, "/etc/init.d/portmap",
               "/etc/rc3.d/S30portmap");

libguestfs は相対パスの使用を拒否します。現在の作業ディレクトリーという概念がありません。

libguestfs
は多くの状況においてエラーを返します。たとえば、ファイルシステムが書き込みできない場合です。または、要求したファイルやディレクトリーが存在しない場合です。
C API (ここにドキュメント化されています)
を使用しているならば、各呼び出しの後でそれらのエラー条件を確認する必要があります。（他の言語バインドは、これらのエラーを例外の中に含めてください。）

ファイルの書き込みはハンドルごとの umask により影響されます。L</guestfs_umask> を呼び出すことにより設定され、初期値は 022
です。 L</UMASK> 参照。

Since libguestfs 1.18, it is possible to mount the libguestfs filesystem on
a local directory, subject to some restrictions.  See L</MOUNT LOCAL> below.

=head2 パーティション

libguestfs はディスクイメージにあるパーティションテーブルを読み込み、作成、変更するための API 呼び出しがあります。

ディスク全体に単一のパーティションを作成したいという一般的な場合、 L</guestfs_part_disk> 呼び出しを使用できます:

 const char *parttype = "mbr";
 if (disk_is_larger_than_2TB)
   parttype = "gpt";
 guestfs_part_disk (g, "/dev/sda", parttype);

以前ディスクイメージにあったものを明示的にすべて効果的に完全消去します。

=head2 LVM2

libguestfs は L</guestfs_lvcreate> および L</guestfs_vgremove> のような、大部分の LVM2
API にアクセスできます。物理ボリューム、ボリュームグループ、論理ボリュームの概念になじみがなければ、役に立たないかもしれません。

この著者はオンラインで L<http://tldp.org/HOWTO/LVM-HOWTO/> にある  LVM HOWTO
を読むことを強く推奨します。

=head2 ダウンロード

Use L</guestfs_cat> to download small, text only files.  This call cannot
handle files containing any ASCII NUL (C<\0>) characters.  However the API
is very simple to use.

L</guestfs_read_file> can be used to read files which contain arbitrary 8
bit data, since it returns a (pointer, size) pair.

L</guestfs_download> can be used to download any file, with no limits on
content or size.

複数のファイルをダウンロードするには L</guestfs_tar_out> および L</guestfs_tgz_out> を参照してください。

=head2 アップロード方法

固定的な内容を持つ小さなファイルを書き込むには、L</guestfs_write> を使用します。すべて 0
のファイルを作成するには、L</guestfs_truncate_size> (スパース) または L</guestfs_fallocate64>
(すべてのブロックを割り当て済み) を使用します。テストファイルを作成するためのさまざまな他の関数があります。たとえば、
L</guestfs_fill> や L</guestfs_fill_pattern> があります。

To upload a single file, use L</guestfs_upload>.  This call has no limits on
file content or size.

複数のファイルをアップロードするには、L</guestfs_tar_in> および L</guestfs_tgz_in> を参照してください。

However the fastest way to upload I<large numbers of arbitrary files> is to
turn them into a squashfs or CD ISO (see L<mksquashfs(8)> and
L<mkisofs(8)>), then attach this using L</guestfs_add_drive_ro>.  If you add
the drive in a predictable way (eg. adding it last after all other drives)
then you can get the device name from L</guestfs_list_devices> and mount it
directly using L</guestfs_mount_ro>.  Note that squashfs images are
sometimes non-portable between kernel versions, and they don't support
labels or UUIDs.  If you want to pre-build an image or you need to mount it
using a label or UUID, use an ISO image instead.

=head2 コピー方法

ファイルとデバイスの間でコピーして、仮想マシンのファイルシステムと入出力するための、さまざまなコマンドがあります。以下の表はその概要です。

=over 4

=item B<ファイル>からB<ファイル>

単一のファイルをコピーするには L</guestfs_cp> を使用します、またはディレクトリーを再帰的にコピーするには
L</guestfs_cp_a> を使用します。

To copy part of a file (offset and size) use L</guestfs_copy_file_to_file>.

=item B<ファイル>からB<デバイス>

=item B<デバイス>からB<ファイル>

=item B<デバイス>からB<デバイス>

L</guestfs_copy_file_to_device>, L</guestfs_copy_device_to_file>, または
L</guestfs_copy_device_to_device> を使用してください。

例: 論理ボリュームの内容の複製:

 guestfs_copy_device_to_device (g,
         "/dev/VG/Original", "/dev/VG/Copy",
         /* -1 marks the end of the list of optional parameters */
         -1);

The destination (F</dev/VG/Copy>) must be at least as large as the source
(F</dev/VG/Original>).  To copy less than the whole source device, use the
optional C<size> parameter:

 guestfs_copy_device_to_device (g,
         "/dev/VG/Original", "/dev/VG/Copy",
         GUESTFS_COPY_DEVICE_TO_DEVICE_SIZE, 10000,
         -1);

=item B<ホストのファイル>からB<ファイルまたはデバイス>

L</guestfs_upload> を使用します。上の L</アップロード方法> 参照。

=item B<ファイルまたはデバイス>からB<ホストのファイル>

L</guestfs_download> を使用します。上の L</ダウンロード方法> 参照。

=back

=head2 UPLOADING AND DOWNLOADING TO PIPES AND FILE DESCRIPTORS

Calls like L</guestfs_upload>, L</guestfs_download>, L</guestfs_tar_in>,
L</guestfs_tar_out> etc appear to only take filenames as arguments, so it
appears you can only upload and download to files.  However many Un*x-like
hosts let you use the special device files F</dev/stdin>, F</dev/stdout>,
F</dev/stderr> and F</dev/fd/N> to read and write from stdin, stdout,
stderr, and arbitrary file descriptor N.

たとえば、L<virt-cat(1)> は次のようにすることにより、出力を標準出力に書き込みます:

 guestfs_download (g, filename, "/dev/stdout");

and you can write tar output to a file descriptor C<fd> by doing:

 char devfd[64];
 snprintf (devfd, sizeof devfd, "/dev/fd/%d", fd);
 guestfs_tar_out (g, "/", devfd);

=head2 ファイルの一覧表示方法

L</guestfs_ll> は人間が読みやすいよう設計されています（おもに L<guestfish(1)> の同等なコマンド C<ll>
を使用するとき）。

L</guestfs_ls> は文字列の平らな一覧のように、ディレクトリーにあるファイルの一覧をプログラムから取得する素早い方法です。

L</guestfs_readdir>
はディレクトリーにあるファイルの一覧、さらにそれぞれに関する追加の情報を取得するためのプログラム的な方法です。ローカルシステムにおける
L<readdir(3)> 呼び出しを使用することとほぼ同様です。

L</guestfs_find> と L</guestfs_find0> は再帰的にファイルを一覧表示するために使用できます。

=head2 コマンドの実行法

libguestfs はおもに仮想マシンの中にあるファイルを操作するための API
です。さらに、仮想マシンの中にあるコマンドを実行するために、限定された機能がいくつかあります。

これには多くの制限があります:

=over 4

=item *

コマンドを実行するカーネルのバージョンは、期待するものにより異なります。

=item *

コマンドがデーモンと通信する必要があれば、ほとんど動作しないでしょう。

=item *

コマンドは制限されたメモリーにおいて実行されます。

=item *

ネットワークは有効にしなければ利用できません（L</guestfs_set_network> 参照）。

=item *

Linux ゲストのみがサポートされます（Windows, BSD など）。

=item *

Architecture limitations (eg. won’t work for a PPC guest on an X86 host).

=item *

For SELinux guests, you may need to relabel the guest after creating new
files.  See L</SELINUX> below.

=item *

I<Security:> It is not safe to run commands from untrusted, possibly
malicious guests.  These commands may attempt to exploit your program by
sending unexpected output.  They could also try to exploit the Linux kernel
or qemu provided by the libguestfs appliance.  They could use the network
provided by the libguestfs appliance to bypass ordinary network partitions
and firewalls.  They could use the elevated privileges or different SELinux
context of your program to their advantage.

A secure alternative is to use libguestfs to install a "firstboot" script (a
script which runs when the guest next boots normally), and to have this
script run the commands you want in the normal context of the running guest,
network security and so on.  For information about other security issues,
see L<guestfs-security(1)>.

=back

The two main API calls to run commands are L</guestfs_command> and
L</guestfs_sh> (there are also variations).

The difference is that L</guestfs_sh> runs commands using the shell, so any
shell globs, redirections, etc will work.

=head2 設定ファイル

To read and write configuration files in Linux guest filesystems, we
strongly recommend using Augeas.  For example, Augeas understands how to
read and write, say, a Linux shadow password file or X.org configuration
file, and so avoids you having to write that code.

The main Augeas calls are bound through the C<guestfs_aug_*> APIs.  We don't
document Augeas itself here because there is excellent documentation on the
L<http://augeas.net/> website.

If you don’t want to use Augeas (you fool!) then try calling
L</guestfs_read_lines> to get the file as a list of lines which you can
iterate over.

=head2 SYSTEMD JOURNAL FILES

To read the systemd journal from a Linux guest, use the C<guestfs_journal_*>
APIs starting with L</guestfs_journal_open>.

Consult the journal documentation here: L<sd-journal(3)>,
L<sd_journal_open(3)>.

=head2 SELinux

We support SELinux guests.  However it is not possible to load the SELinux
policy of the guest into the appliance kernel.  Therefore the strategy for
dealing with SELinux guests is to relabel them after making changes.

In libguestfs E<ge> 1.34 there is a new API, L</guestfs_setfiles>, which can
be used for this.  To properly use this API you have to parse the guest
SELinux configuration.  See the L<virt-customize(1)> module
F<customize/SELinux_relabel.ml> for how to do this.

A simpler but slower alternative is to touch F</.autorelabel> in the guest,
which means that the guest will relabel itself at next boot.

Libguestfs E<le> 1.32 had APIs C<guestfs_set_selinux>,
C<guestfs_get_selinux>, C<guestfs_setcon> and C<guestfs_getcon>.  These did
not work properly, are deprecated, and should not be used in new code.

=head2 umask

Certain calls are affected by the current file mode creation mask (the
"umask").  In particular ones which create files or directories, such as
L</guestfs_touch>, L</guestfs_mknod> or L</guestfs_mkdir>.  This affects
either the default mode that the file is created with or modifies the mode
that you supply.

umask の初期値は C<022> です、そのためファイルは C<0644> のようなモードで作成され、ディレクトリーは C<0755> です。

umask による影響を避けるには 2 つの方法があります。1 つは umask を 0 に設定することです（開始後の早いうちに
C<guestfs_umask (g, 0)> を呼び出します）。もう 1 つは各ファイルまたはディレクトリーを作成した後に
L</guestfs_chmod> を呼び出すことです。

umask に関する詳細は L<umask(2)> を参照してください。

=head2 LABELS AND UUIDS

Many filesystems, devices and logical volumes support either labels (short
strings like "BOOT" which might not be unique) and/or UUIDs (globally unique
IDs).

For filesystems, use L</guestfs_vfs_label> or L</guestfs_vfs_uuid> to read
the label or UUID.  Some filesystems let you call L</guestfs_set_label> or
L</guestfs_set_uuid> to change the label or UUID.

You can locate a filesystem by its label or UUID using
L</guestfs_findfs_label> or L</guestfs_findfs_uuid>.

For LVM2 (which supports only UUIDs), there is a rich set of APIs for
fetching UUIDs, fetching UUIDs of the contained objects, and changing
UUIDs.  See: L</guestfs_lvuuid>, L</guestfs_vguuid>, L</guestfs_pvuuid>,
L</guestfs_vglvuuids>, L</guestfs_vgpvuuids>, L</guestfs_vgchange_uuid>,
L</guestfs_vgchange_uuid_all>, L</guestfs_pvchange_uuid>,
L</guestfs_pvchange_uuid_all>.

Note when cloning a filesystem, device or whole guest, it is a good idea to
set new randomly generated UUIDs on the copy.

=head2 暗号化ディスク

Libguestfs allows you to access Linux guests which have been encrypted using
whole disk encryption that conforms to the Linux Unified Key Setup (LUKS)
standard.  This includes nearly all whole disk encryption systems used by
modern Linux guests.

LUKS 暗号化ブロックデバイス（それは文字列 C<crypto_LUKS> を返します）を識別するには L</guestfs_vfs_type>
を使用します。

そして L</guestfs_luks_open> を呼び出すことにより、これらのデバイスを開きます。明示的にパスフレーズが必要です。

Opening a LUKS device creates a new device mapper device called
F</dev/mapper/mapname> (where C<mapname> is the string you supply to
L</guestfs_luks_open>).  Reads and writes to this mapper device are
decrypted from and encrypted to the underlying block device respectively.

LVM volume groups on the device can be made visible by calling
L</guestfs_vgscan> followed by L</guestfs_vg_activate_all>.  The logical
volume(s) can now be mounted in the usual way.

Use the reverse process to close a LUKS device.  Unmount any logical volumes
on it, deactivate the volume groups by calling C<guestfs_vg_activate (g, 0,
["/dev/VG"])>.  Then close the mapper device by calling
L</guestfs_luks_close> on the F</dev/mapper/mapname> device (I<not> the
underlying encrypted block device).

=head2 MOUNT LOCAL

In libguestfs E<ge> 1.18, it is possible to mount the libguestfs filesystem
on a local directory and access it using ordinary POSIX calls and programs.

Availability of this is subject to a number of restrictions: it requires
FUSE (the Filesystem in USErspace), and libfuse must also have been
available when libguestfs was compiled.  FUSE may require that a kernel
module is loaded, and it may be necessary to add the current user to a
special C<fuse> group.  See the documentation for your distribution and
L<http://fuse.sf.net> for further information.

The call to mount the libguestfs filesystem on a local directory is
L</guestfs_mount_local> (q.v.) followed by L</guestfs_mount_local_run>.  The
latter does not return until you unmount the filesystem.  The reason is that
the call enters the FUSE main loop and processes kernel requests, turning
them into libguestfs calls.  An alternative design would have been to create
a background thread to do this, but libguestfs doesn't require pthreads.
This way is also more flexible: for example the user can create another
thread for L</guestfs_mount_local_run>.

L</guestfs_mount_local> needs a certain amount of time to set up the
mountpoint.  The mountpoint is not ready to use until the call returns.  At
this point, accesses to the filesystem will block until the main loop is
entered (ie. L</guestfs_mount_local_run>).  So if you need to start another
process to access the filesystem, put the fork between
L</guestfs_mount_local> and L</guestfs_mount_local_run>.

=head3 MOUNT LOCAL COMPATIBILITY

Since local mounting was only added in libguestfs 1.18, and may not be
available even in these builds, you should consider writing code so that it
doesn't depend on this feature, and can fall back to using libguestfs file
system calls.

If libguestfs was compiled without support for L</guestfs_mount_local> then
calling it will return an error with errno set to C<ENOTSUP> (see
L</guestfs_last_errno>).

=head3 MOUNT LOCAL PERFORMANCE

Libguestfs on top of FUSE performs quite poorly.  For best performance do
not use it.  Use ordinary libguestfs filesystem calls, upload, download
etc. instead.

=head2 HOTPLUGGING

In libguestfs E<ge> 1.20, you may add drives and remove after calling
L</guestfs_launch>.  There are some restrictions, see below.  This is called
I<hotplugging>.

Only a subset of the backends support hotplugging (currently only the
libvirt backend has support).  It also requires that you use libvirt E<ge>
0.10.3 and qemu E<ge> 1.2.

To hot-add a disk, simply call L</guestfs_add_drive_opts> after
L</guestfs_launch>.  It is mandatory to specify the C<label> parameter so
that the newly added disk has a predictable name.  For example:

 if (guestfs_launch (g) == -1)
   error ("launch failed");
 
 if (guestfs_add_drive_opts (g, filename,
                             GUESTFS_ADD_DRIVE_OPTS_LABEL, "newdisk",
                             -1) == -1)
   error ("hot-add of disk failed");
 
 if (guestfs_part_disk ("/dev/disk/guestfs/newdisk", "mbr") == -1)
   error ("partitioning of hot-added disk failed");

To hot-remove a disk, call L</guestfs_remove_drive>.  You can call this
before or after L</guestfs_launch>.  You can only remove disks that were
previously added with a label.

Backends that support hotplugging do not require that you add E<ge> 1 disk
before calling launch.  When hotplugging is supported you don't need to add
any disks.

=head2 REMOTE STORAGE

=head3 CEPH

Libguestfs can access Ceph (librbd/RBD) disks.

To do this, set the optional C<protocol> and C<server> parameters of
L</guestfs_add_drive_opts> like this:

 char **servers = { "ceph1.example.org:3000", /* ... */, NULL };
 guestfs_add_drive_opts (g, "pool/image",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "rbd",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, servers,
                         GUESTFS_ADD_DRIVE_OPTS_USERNAME, "rbduser",
                         GUESTFS_ADD_DRIVE_OPTS_SECRET, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==",
                         -1);

C<servers> (the C<server> parameter) is a list of one or more Ceph servers.
The server string is documented in L</guestfs_add_drive_opts>. The
C<username> and C<secret> parameters are also optional, and if not given,
then no authentication will be used.

=head3 FTP, HTTP AND TFTP

Libguestfs can access remote disks over FTP, FTPS, HTTP, HTTPS or TFTP
protocols.

To do this, set the optional C<protocol> and C<server> parameters of
L</guestfs_add_drive_opts> like this:

 char **servers = { "www.example.org", NULL };
 guestfs_add_drive_opts (g, "/disk.img",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "http",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, servers,
                         -1);

The C<protocol> can be one of C<"ftp">, C<"ftps">, C<"http">, C<"https"> or
C<"tftp">.

C<servers> (the C<server> parameter) is a list which must have a single
element.  The single element is a string defining the web, FTP or TFTP
server.  The format of this string is documented in
L</guestfs_add_drive_opts>.

=head3 GLUSTER

Libguestfs can access Gluster disks.

To do this, set the optional C<protocol> and C<server> parameters of
L</guestfs_add_drive_opts> like this:

 char **servers = { "gluster.example.org:24007", NULL };
 guestfs_add_drive_opts (g, "volname/image",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "gluster",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, servers,
                         -1);

C<servers> (the C<server> parameter) is a list which must have a single
element.  The single element is a string defining the Gluster server.  The
format of this string is documented in L</guestfs_add_drive_opts>.

Note that gluster usually requires the client process (ie. libguestfs)  to
run as B<root> and will give unfathomable errors if it is not (eg. "No data
available").

=head3 ISCSI

Libguestfs can access iSCSI disks remotely.

To do this, set the optional C<protocol> and C<server> parameters like this:

 char **server = { "iscsi.example.org:3000", NULL };
 guestfs_add_drive_opts (g, "target-iqn-name/lun",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "iscsi",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, server,
                         -1);

The C<server> parameter is a list which must have a single element.  The
single element is a string defining the iSCSI server.  The format of this
string is documented in L</guestfs_add_drive_opts>.

=head3 NETWORK BLOCK DEVICE

Libguestfs can access Network Block Device (NBD) disks remotely.

To do this, set the optional C<protocol> and C<server> parameters of
L</guestfs_add_drive_opts> like this:

 char **server = { "nbd.example.org:3000", NULL };
 guestfs_add_drive_opts (g, "" /* export name - see below */,
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "nbd",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, server,
                         -1);

注:

=over 4

=item *

C<server> is in fact a list of servers.  For NBD you must always supply a
list with a single element.  (Other remote protocols require zero or more
than one server, hence the requirement for this parameter to be a list).

=item *

The C<server> string is documented in L</guestfs_add_drive_opts>.  To
connect to a local qemu-nbd instance over a Unix domain socket, use
C<"unix:/path/to/socket">.

=item *

The C<filename> parameter is the NBD export name.  Use an empty string to
mean the default export.  Many NBD servers, including qemu-nbd, do not
support export names.

=item *

If using qemu-nbd as your server, you should always specify the C<-t>
option.  The reason is that libguestfs may open several connections to the
server.

=item *

The libvirt backend requires that you set the C<format> parameter of
L</guestfs_add_drive_opts> accurately when you use writable NBD disks.

=item *

The libvirt backend has a bug that stops Unix domain socket connections from
working: L<https://bugzilla.redhat.com/show_bug.cgi?id=922888>

=item *

The direct backend does not support readonly connections because of a bug in
qemu: L<https://bugs.launchpad.net/qemu/+bug/1155677>

=back

=head3 SHEEPDOG

Libguestfs can access Sheepdog disks.

To do this, set the optional C<protocol> and C<server> parameters of
L</guestfs_add_drive_opts> like this:

 char **servers = { /* optional servers ... */ NULL };
 guestfs_add_drive_opts (g, "volume",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "sheepdog",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, servers,
                         -1);

The optional list of C<servers> may be zero or more server addresses
(C<"hostname:port">).  The format of the server strings is documented in
L</guestfs_add_drive_opts>.

=head3 SSH

Libguestfs can access disks over a Secure Shell (SSH) connection.

To do this, set the C<protocol> and C<server> and (optionally)  C<username>
parameters of L</guestfs_add_drive_opts> like this:

 char **server = { "remote.example.com", NULL };
 guestfs_add_drive_opts (g, "/path/to/disk.img",
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                         GUESTFS_ADD_DRIVE_OPTS_PROTOCOL, "ssh",
                         GUESTFS_ADD_DRIVE_OPTS_SERVER, server,
                         GUESTFS_ADD_DRIVE_OPTS_USERNAME, "remoteuser",
                         -1);

The format of the server string is documented in L</guestfs_add_drive_opts>.

=head2 INSPECTION

Libguestfs has APIs for inspecting an unknown disk image to find out if it
contains operating systems, an install CD or a live CD.

Add all disks belonging to the unknown virtual machine and call
L</guestfs_launch> in the usual way.

Then call L</guestfs_inspect_os>.  This function uses other libguestfs calls
and certain heuristics, and returns a list of operating systems that were
found.  An empty list means none were found.  A single element is the root
filesystem of the operating system.  For dual- or multi-boot guests,
multiple roots can be returned, each one corresponding to a separate
operating system.  (Multi-boot virtual machines are extremely rare in the
world of virtualization, but since this scenario can happen, we have built
libguestfs to deal with it.)

For each root, you can then call various C<guestfs_inspect_get_*> functions
to get additional details about that operating system.  For example, call
L</guestfs_inspect_get_type> to return the string C<windows> or C<linux> for
Windows and Linux-based operating systems respectively.

Un*x-like and Linux-based operating systems usually consist of several
filesystems which are mounted at boot time (for example, a separate boot
partition mounted on F</boot>).  The inspection rules are able to detect how
filesystems correspond to mount points.  Call
C<guestfs_inspect_get_mountpoints> to get this mapping.  It might return a
hash table like this example:

 /boot => /dev/sda1
 /     => /dev/vg_guest/lv_root
 /usr  => /dev/vg_guest/lv_usr

The caller can then make calls to L</guestfs_mount> to mount the filesystems
as suggested.

Be careful to mount filesystems in the right order (eg. F</> before
F</usr>).  Sorting the keys of the hash by length, shortest first, should
work.

Inspection currently only works for some common operating systems.
Contributors are welcome to send patches for other operating systems that we
currently cannot detect.

暗号化ディスクは検査の前に開く必要があります。詳細はL</暗号化ディスク>を参照してください。L</guestfs_inspect_os>
関数はすべての暗号化デバイスを単に無視します。

A note on the implementation: The call L</guestfs_inspect_os> performs
inspection and caches the results in the guest handle.  Subsequent calls to
C<guestfs_inspect_get_*> return this cached information, but I<do not>
re-read the disks.  If you change the content of the guest disks, you can
redo inspection by calling L</guestfs_inspect_os> again.
(L</guestfs_inspect_list_applications2> works a little differently from the
other calls and does read the disks.  See documentation for that function
for details).

=head3 インストールディスクの検査方法

libguestfs (1.9.4以降) は、いくつかのインストールディスク、インストール CD、live CD などを検知できます。

Further information is available about the operating system that can be
installed using the regular inspection APIs like
L</guestfs_inspect_get_product_name>, L</guestfs_inspect_get_major_version>
etc.

=head2 SPECIAL CONSIDERATIONS FOR WINDOWS GUESTS

libguestfs は NTFS パーティションをマウントできます。そのためには L<http://www.ntfs-3g.org/>
ドライバーを使用します。

=head3 ドライブレターとパス

DOS and Windows still use drive letters, and the filesystems are always
treated as case insensitive by Windows itself, and therefore you might find
a Windows configuration file referring to a path like
C<c:\windows\system32>.  When the filesystem is mounted in libguestfs, that
directory might be referred to as F</WINDOWS/System32>.

Drive letter mappings can be found using inspection (see L</INSPECTION> and
L</guestfs_inspect_get_drive_mappings>)

Dealing with separator characters (backslash vs forward slash) is outside
the scope of libguestfs, but usually a simple character replacement will
work.

To resolve the case insensitivity of paths, call
L</guestfs_case_sensitive_path>.

=head3 LONG FILENAMES ON NTFS

NTFS supports filenames up to 255 characters long.  "Character" means a 2
byte UTF-16 codepoint which can encode the most common Unicode codepoints.

Most Linux filesystems support filenames up to 255 I<bytes>.  This means you
may get an error:

 File name too long

when you copy a file from NTFS to a Linux filesystem if the name, when
reencoded as UTF-8, would exceed 255 bytes in length.

This will most often happen when using non-ASCII names that are longer than
~127 characters (eg. Greek, Cyrillic) or longer than ~85 characters (Asian
languages).

A workaround is not to try to store such long filenames on Linux native
filesystems.  Since the L<tar(1)> format can store unlimited length
filenames, keep the files in a tarball.

=head3 Windows レジストリのアクセス方法

Libguestfs also provides some help for decoding Windows Registry "hive"
files, through a separate C library called L<hivex(3)>.

Before libguestfs 1.19.35 you had to download the hive file, operate on it
locally using hivex, and upload it again.  Since this version, we have
included the major hivex APIs directly in the libguestfs API (see
L</guestfs_hivex_open>).  This means that if you have opened a Windows
guest, you can read and write the registry directly.

L<virt-win-reg(1)> 参照。

=head3 NTFS-3G ファイルシステムにおけるシンボリックリンク

Ntfs-3g tries to rewrite "Junction Points" and NTFS "symbolic links" to
provide something which looks like a Linux symlink.  The way it tries to do
the rewriting is described here:

L<http://www.tuxera.com/community/ntfs-3g-advanced/junction-points-and-symbolic-links/>

The essential problem is that ntfs-3g simply does not have enough
information to do a correct job.  NTFS links can contain drive letters and
references to external device GUIDs that ntfs-3g has no way of resolving.
It is almost certainly the case that libguestfs callers should ignore what
ntfs-3g does (ie. don't use L</guestfs_readlink> on NTFS volumes).

Instead if you encounter a symbolic link on an ntfs-3g filesystem, use
L</guestfs_lgetxattr> to read the C<system.ntfs_reparse_data> extended
attribute, and read the raw reparse data from that (you can find the format
documented in various places around the web).

=head3 EXTENDED ATTRIBUTES ON NTFS-3G FILESYSTEMS

There are other useful extended attributes that can be read from ntfs-3g
filesystems (using L</guestfs_getxattr>).  See:

L<http://www.tuxera.com/community/ntfs-3g-advanced/extended-attributes/>

=head3 WINDOWS HIBERNATION AND WINDOWS 8 FAST STARTUP

Windows guests which have been hibernated (instead of fully shut down)
cannot be mounted.  This is a limitation of ntfs-3g.  You will see an error
like this:

 The disk contains an unclean file system (0, 0).
 Metadata kept in Windows cache, refused to mount.
 Failed to mount '/dev/sda2': Operation not permitted
 The NTFS partition is in an unsafe state. Please resume
 and shutdown Windows fully (no hibernation or fast
 restarting), or mount the volume read-only with the
 'ro' mount option.

Windows 8 では、シャットダウンボタンを押しても仮想マシンがシャットダウンしません。代わりに、仮想マシンが休止状態になります。これは
"高速スタートアップ" として知られています。

いくつかの推奨される回避策があります:

=over 4

=item *

読み込み専用でマウントします (例: L</guestfs_mount_ro>)。

=item *

On Windows 8, turn off fast startup.  It is in the Control Panel → Power
Options → Choose what the power buttons do → Change settings that are
currently unavailable → Turn on fast startup.

=item *

On Windows 7 and earlier, shut the guest off properly instead of hibernating
it.

=back

=head2 RESIZE2FS ERRORS

The L</guestfs_resize2fs>, L</guestfs_resize2fs_size> and
L</guestfs_resize2fs_M> calls are used to resize ext2/3/4 filesystems.

The underlying program (L<resize2fs(8)>) requires that the filesystem is
clean and recently fsck'd before you can resize it.  Also, if the resize
operation fails for some reason, then you had to call fsck the filesystem
again to fix it.

In libguestfs C<lt> 1.17.14, you usually had to call L</guestfs_e2fsck_f>
before the resize.  However, in C<ge> 1.17.14, L<e2fsck(8)> is called
automatically before the resize, so you no longer need to do this.

The L<resize2fs(8)> program can still fail, in which case it prints an error
message similar to:

 容量変更の操作を中断した後、ファイルシステムを
 修復するために 'e2fsck -fy <device>' を実行してください。

You can do this by calling L</guestfs_e2fsck> with the C<forceall> option.
However in the context of disk images, it is usually better to avoid this
situation, eg. by rolling back to an earlier snapshot, or by copying and
resizing and on failure going back to the original.

=head2 USING LIBGUESTFS WITH OTHER PROGRAMMING LANGUAGES

Although we don’t want to discourage you from using the C API, we will
mention here that the same API is also available in other languages.

The API is broadly identical in all supported languages.  This means that
the C call C<guestfs_add_drive_ro(g,file)> is C<$g-E<gt>add_drive_ro($file)>
in Perl, C<g.add_drive_ro(file)> in Python, and C<g#add_drive_ro file> in
OCaml.  In other words, a straightforward, predictable isomorphism between
each language.

Error messages are automatically transformed into exceptions if the language
supports it.

We don’t try to "object orientify" parts of the API in OO languages,
although contributors are welcome to write higher level APIs above what we
provide in their favourite languages if they wish.

=over 4

=item B<C++>

C++ プログラムから I<guestfs.h> ヘッダーファイルを使用できます。 C++ API は C API と同一です。 C++
のクラスと例外は使用されません。

=item B<C#>

The C# bindings are highly experimental.  Please read the warnings at the
top of F<csharp/Libguestfs.cs>.

=item B<Erlang>

L<guestfs-erlang(3)> 参照。

=item B<GObject>

Experimental GObject bindings (with GObject Introspection support) are
available.

See L<guestfs-gobject(3)>.

=item B<Go>

See L<guestfs-golang(3)>.

=item B<Haskell>

This language binding is working but incomplete:

=over 4

=item *

Functions with optional arguments are not bound.  Implementing optional
arguments in Haskell seems to be very complex.

=item *

Events are not bound.

=item *

Functions with the following return types are not bound:

=over 4

=item *

Any function returning a struct.

=item *

Any function returning a list of structs.

=item *

A few functions that return fixed length buffers (specifically ones declared
C<RBufferOut> in the generator).

=item *

A tiny number of obscure functions that return constant strings
(specifically ones declared C<RConstOptString> in the generator).

=back

=back

=item B<Java>

Full documentation is contained in the Javadoc which is distributed with
libguestfs.  For examples, see L<guestfs-java(3)>.

=item B<Lua>

L<guestfs-lua(3)> 参照。

=item B<OCaml>

L<guestfs-ocaml(3)> 参照。

=item B<Perl>

L<guestfs-perl(3)> および L<Sys::Guestfs(3)> 参照。

=item B<PHP>

For documentation see C<README-PHP> supplied with libguestfs sources or in
the php-libguestfs package for your distribution.

PHP バインドは 64 ビットマシンにおいてのみ正しく動作します。

=item B<Python>

L<guestfs-python(3)> 参照。

=item B<Ruby>

L<guestfs-ruby(3)> 参照。

JRuby に対しては Java バインドを使用します。

=item B<シェルスクリプト>

L<guestfish(1)> 参照。

=back

=head2 LIBGUESTFS GOTCHAS

L<http://en.wikipedia.org/wiki/Gotcha_(programming)>: "A feature of a system
[...] that works in the way it is documented but is counterintuitive and
almost invites mistakes."

Since we developed libguestfs and the associated tools, there are several
things we would have designed differently, but are now stuck with for
backwards compatibility or other reasons.  If there is ever a libguestfs 2.0
release, you can expect these to change.  Beware of them.

=over 4

=item 初期値は読み込み専用です。

L<guestfish(3)> では、 I<--ro> が初期値です。イメージを変更したいならば I<--rw> を指定する必要があります。

これにより、動作中の仮想マシンのイメージを破壊する可能性を減らします。

Note that many filesystems change the disk when you just mount and unmount,
even if you didn't perform any writes.  You need to use
L</guestfs_add_drive_ro> to guarantee that the disk is not changed.

=item guestfish コマンドラインは使うのが難しいです。

F<guestfish disk.img> doesn't do what people expect (open F<disk.img> for
examination).  It tries to run a guestfish command F<disk.img> which doesn't
exist, so it fails.  In earlier versions of guestfish the error message was
also unintuitive, but we have corrected this since.  Like the Bourne shell,
we should have used C<guestfish -c command> to run commands.

=item guestfish megabyte modifiers don’t work right on all commands

In recent guestfish you can use C<1M> to mean 1 megabyte (and similarly for
other modifiers).  What guestfish actually does is to multiply the number
part by the modifier part and pass the result to the C API.  However this
doesn't work for a few APIs which aren't expecting bytes, but are already
expecting some other unit (eg. megabytes).

最も一般的な L</guestfs_lvcreate> です。 guestfish コマンド:

 lvcreate LV VG 100M

does not do what you might expect.  Instead because L</guestfs_lvcreate> is
already expecting megabytes, this tries to create a 100 I<terabyte> (100
megabytes * megabytes) logical volume.  The error message you get from this
is also a little obscure.

This could be fixed in the generator by specially marking parameters and
return values which take bytes or other units.

=item Ambiguity between devices and paths

There is a subtle ambiguity in the API between a device name
(eg. F</dev/sdb2>) and a similar pathname.  A file might just happen to be
called C<sdb2> in the directory F</dev> (consider some non-Unix VM image).

In the current API we usually resolve this ambiguity by having two separate
calls, for example L</guestfs_checksum> and L</guestfs_checksum_device>.
Some API calls are ambiguous and (incorrectly) resolve the problem by
detecting if the path supplied begins with F</dev/>.

To avoid both the ambiguity and the need to duplicate some calls, we could
make paths/devices into structured names.  One way to do this would be to
use a notation like grub (C<hd(0,0)>), although nobody really likes this
aspect of grub.  Another way would be to use a structured type, equivalent
to this OCaml type:

 type path = Path of string | Device of int | Partition of int * int

which would allow you to pass arguments like:

 Path "/foo/bar"
 Device 1            (* /dev/sdb, または場合によると /dev/sda *)
 Partition (1, 2)    (* /dev/sdb2 (または /dev/sda2 や /dev/sdb3?) *)
 Path "/dev/sdb2"    (* デバイスではありません *)

As you can see there are still problems to resolve even with this
representation.  Also consider how it might work in guestfish.

=back

=head2 キーとパスフレーズ

特定の libguestfs 呼び出しは、C 文字列のように渡される、秘密を扱うキーの材料を含むパラメーターをとります。

In the future we would hope to change the libguestfs implementation so that
keys are L<mlock(2)>-ed into physical RAM, and thus can never end up in
swap.  However this is I<not> done at the moment, because of the complexity
of such an implementation.

Therefore you should be aware that any key parameter you pass to libguestfs
might end up being written out to the swap partition.  If this is a concern,
scrub the swap partition or don't use libguestfs on encrypted devices.

=head2 MULTIPLE HANDLES AND MULTIPLE THREADS

All high-level libguestfs actions are synchronous.  If you want to use
libguestfs asynchronously then you must create a thread.

=head3 Threads in libguestfs E<ge> 1.38

In libguestfs E<ge> 1.38, each handle (C<guestfs_h>) contains a lock which
is acquired automatically when you call a libguestfs function.  The
practical effect of this is you can call libguestfs functions with the same
handle from multiple threads without needing to do any locking.

Also in libguestfs E<ge> 1.38, the last error on the handle
(L</guestfs_last_error>, L</guestfs_last_errno>) is stored in thread-local
storage, so it is safe to write code like:

 if (guestfs_add_drive_ro (g, drive) == -1)
   fprintf (stderr, "error was: %s\n", guestfs_last_error (g));

even when other threads may be concurrently using the same handle C<g>.

=head3 Threads in libguestfs E<lt> 1.38

In libguestfs E<lt> 1.38, you must use the handle only from a single
thread.  Either use the handle exclusively from one thread, or provide your
own mutex so that two threads cannot issue calls on the same handle at the
same time.  Even apparently innocent functions like L</guestfs_get_trace>
are I<not> safe to be called from multiple threads without a mutex in
libguestfs E<lt> 1.38.

Use L</guestfs_set_identifier> to make it simpler to identify threads in
trace output.

=head2 パス

Libguestfs needs a supermin appliance, which it finds by looking along an
internal path.

By default it looks for these in the directory C<$libdir/guestfs>
(eg. F</usr/local/lib/guestfs> or F</usr/lib64/guestfs>).

Use L</guestfs_set_path> or set the environment variable L</LIBGUESTFS_PATH>
to change the directories that libguestfs will search in.  The value is a
colon-separated list of paths.  The current directory is I<not> searched
unless the path contains an empty element or C<.>.  For example
C<LIBGUESTFS_PATH=:/usr/lib/guestfs> would search the current directory and
then F</usr/lib/guestfs>.

=head2 QEMU ラッパー

自身の QEMU をコンパイルしたい、非標準の場所から QEMU を実行したい、または追加の引数を QEMU に渡したいならば、QEMU
のシェルスクリプト・ラッパーを書けます。

There is one important rule to remember: you I<must C<exec qemu>> as the
last command in the shell script (so that qemu replaces the shell and
becomes the direct child of the libguestfs-using program).  If you don't do
this, then the qemu process won't be cleaned up correctly.

Here is an example of a wrapper, where I have built my own copy of qemu from
source:

 #!/bin/sh -
 qemudir=/home/rjones/d/qemu
 exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"

Save this script as F</tmp/qemu.wrapper> (or wherever), C<chmod +x>, and
then use it by setting the LIBGUESTFS_HV environment variable.  For example:

 LIBGUESTFS_HV=/tmp/qemu.wrapper guestfish

Note that libguestfs also calls qemu with the -help and -version options in
order to determine features.

Wrappers can also be used to edit the options passed to qemu.  In the
following example, the C<-machine ...> option (C<-machine> and the following
argument) are removed from the command line and replaced with C<-machine
pc,accel=tcg>.  The while loop iterates over the options until it finds the
right one to remove, putting the remaining options into the C<args> array.

 #!/bin/bash -
 
 i=0
 while [ $# -gt 0 ]; do
     case "$1" in
     -machine)
         shift 2;;
     *)
         args[i]="$1"
         (( i++ ))
         shift ;;
     esac
 done
 
 exec qemu-kvm -machine pc,accel=tcg "${args[@]}"

=begin HTML

<!-- old anchor for the next section --> <a name="attach-method"/>

=end HTML

=head2 BACKEND

The backend (previously known as the "attach method") controls how
libguestfs creates and/or connects to the backend daemon, eg. by starting
qemu directly, or using libvirt to manage an appliance, running User-Mode
Linux, or connecting to an already running daemon.

You can set the backend by calling L</guestfs_set_backend>, or by setting
the environment variable C<LIBGUESTFS_BACKEND>.

Possible backends are described below:

=over 4

=item C<direct>

=item C<appliance>

Run qemu directly to launch an appliance.

C<direct> and C<appliance> are synonyms.

This is the ordinary method and normally the default, but see the note
below.

=item C<libvirt>

=item C<libvirt:null>

=item C<libvirt:I<URI>>

Use libvirt to launch and manage the appliance.

C<libvirt> causes libguestfs to choose a suitable URI for creating session
guests.  If using the libvirt backend, you almost always should use this.

C<libvirt:null> causes libguestfs to use the C<NULL> connection URI, which
causes libvirt to try to guess what the user meant.  You probably don't want
to use this.

C<libvirt:I<URI>> uses I<URI> as the libvirt connection URI (see
L<http://libvirt.org/uri.html>).  The typical libvirt backend with a URI
would be C<libvirt:qemu:///session>

The libvirt backend supports more features, including hotplugging (see
L</HOTPLUGGING>) and sVirt.

=item C<uml>

Run the User-Mode Linux kernel.  The location of the kernel is set using
C<$LIBGUESTFS_HV> or using the L</guestfs_set_qemu> API (note that qemu is
not involved, we just reuse the same variable in the handle for
convenience).

User-Mode Linux can be much faster, simpler and more lightweight than using
a full-blown virtual machine, but it also has some shortcomings.  See
L</USER-MODE LINUX BACKEND> below.

=item C<unix:I<path>>

Unix ドメイン・ソケット I<path> に接続します。

This method lets you connect to an existing daemon or (using virtio-serial)
to a live guest.  For more information, see L</ATTACHING TO RUNNING
DAEMONS>.

=back

C<direct> is usually the default backend.  However since libguestfs E<ge>
1.19.24, libguestfs can be built with a different default by doing:

 ./configure --with-default-backend=...

To find out if libguestfs was compiled with a different default backend, do:

 unset LIBGUESTFS_BACKEND
 guestfish get-backend

=head2 BACKEND SETTINGS

Each backend can be configured by passing a list of strings.  You can either
call L</guestfs_set_backend_settings> with a list of strings, or set the
C<LIBGUESTFS_BACKEND_SETTINGS> environment variable to a colon-separated
list of strings (before creating the handle).

=head3 force_tcg

Using:

 export LIBGUESTFS_BACKEND_SETTINGS=force_tcg

will force the direct and libvirt backends to use TCG (software emulation)
instead of KVM (hardware accelerated virtualization).

=head3 gdb

The direct backend supports:

 export LIBGUESTFS_BACKEND_SETTINGS=gdb

When this is set, qemu will not start running the appliance immediately.  It
will wait for you to connect to it using gdb:

 $ gdb
 (gdb) symbol-file /path/to/vmlinux
 (gdb) target remote tcp::1234
 (gdb) cont

You can then debug the appliance kernel, which is useful to debug boot
failures (especially ones where there are no debug messages printed - tip:
look in the kernel C<log_buf>).

On Fedora, install C<kernel-debuginfo> for the C<vmlinux> file (containing
symbols).  Make sure the symbols precisely match the kernel being used.

=head2 ATTACHING TO RUNNING DAEMONS

I<Note (1):> This is B<highly experimental> and has a tendency to eat
babies.  Use with caution.

I<Note (2):> This section explains how to attach to a running daemon from a
low level perspective.  For most users, simply using virt tools such as
L<guestfish(1)> with the I<--live> option will "just work".

=head3 Using guestfs_set_backend

By calling L</guestfs_set_backend> you can change how the library connects
to the C<guestfsd> daemon in L</guestfs_launch> (read
L<guestfs-internals(1)/ARCHITECTURE> for some background).

The normal backend is C<direct>, where a small appliance is created
containing the daemon, and then the library connects to this.  C<libvirt> or
C<libvirt:I<URI>> are alternatives that use libvirt to start the appliance.

Setting the backend to C<unix:I<path>> (where I<path> is the path of a Unix
domain socket) causes L</guestfs_launch> to connect to an existing daemon
over the Unix domain socket.

The normal use for this is to connect to a running virtual machine that
contains a C<guestfsd> daemon, and send commands so you can read and write
files inside the live virtual machine.

=head3 live フラグを用いた guestfs_add_domain の使用方法

L</guestfs_add_domain> provides some help for getting the correct backend.
If you pass the C<live> option to this function, then (if the virtual
machine is running) it will examine the libvirt XML looking for a
virtio-serial channel to connect to:

 <domain>
   ...
   <devices>
     ...
     <channel type='unix'>
       <source mode='bind' path='/path/to/socket'/>
       <target type='virtio' name='org.libguestfs.channel.0'/>
     </channel>
     ...
   </devices>
 </domain>

L</guestfs_add_domain> extracts F</path/to/socket> and sets the backend to
C<unix:/path/to/socket>.

Some of the libguestfs tools (including guestfish) support a I<--live>
option which is passed through to L</guestfs_add_domain> thus allowing you
to attach to and modify live virtual machines.

The virtual machine needs to have been set up beforehand so that it has the
virtio-serial channel and so that guestfsd is running inside it.

=head2 USER-MODE LINUX BACKEND

Setting the following environment variables (or the equivalent in the API)
selects the User-Mode Linux backend:

 export LIBGUESTFS_BACKEND=uml
 export LIBGUESTFS_HV=/path/to/vmlinux

C<vmlinux> (or it may be called C<linux>) is the Linux binary, compiled to
run as a userspace process.  Note that we reuse the qemu variable in the
handle for convenience; qemu is not involved.

User-Mode Linux can be faster and more lightweight than running a full-blown
virtual machine as the backend (especially if you are already running
libguestfs in a virtual machine or cloud instance), but it also has some
shortcomings compared to the usual qemu/KVM-based backend.

=head3 BUILDING USER-MODE LINUX FROM SOURCE

Your Linux distro may provide UML in which case you can ignore this section.

These instructions are adapted from:
L<http://user-mode-linux.sourceforge.net/source.html>

=over 4

=item 1. Check out Linux sources

Clone the Linux git repository or download the Linux source tarball.

=item 2. Configure the kernel

B<Note:> All ‘make’ commands must have C<ARCH=um> added.

 make menuconfig ARCH=um

Make sure any filesystem drivers that you need are compiled into the kernel.

B<Currently, it needs a large amount of extra work to get modules working>.
It’s recommended that you disable module support in the kernel
configuration, which will cause everything to be compiled into the image.

=item 3. Build the kernel

 make ARCH=um

This will leave a file called C<linux> or C<vmlinux> in the top-level
directory.  This is the UML kernel.  You should set C<LIBGUESTFS_HV> to
point to this file.

=back

=head3 USER-MODE LINUX DIFFERENCES FROM KVM

=over 4

=item UML only supports raw-format images

Only plain raw-format images will work.  No qcow2, no backing files.

=item UML does not support any remote drives

No NBD, etc.

=item UML only works on ix86 and x86-64

=item UML is experimental

In particular, support for UML in libguestfs depends on support for UML in
the upstream kernel.  If UML was ever removed from the upstream Linux
kernel, then we might remove it from libguestfs too.

=back

=head2 ABI 保証

We guarantee the libguestfs ABI (binary interface), for public, high-level
actions as outlined in this section.  Although we will deprecate some
actions, for example if they get replaced by newer calls, we will keep the
old actions forever.  This allows you the developer to program in confidence
against the libguestfs API.

=head2 ブロックデバイスの命名法

Libguestfs defines F</dev/sd*> as the I<standard naming scheme> for devices
passed to API calls.  So F</dev/sda> means "the first device added by
L</guestfs_add_drive_opts>", and F</dev/sdb3> means "the third partition on
the second device".

Internally device names are sometimes translated, but this should not be
visible at the API level.

=head3 ディスクラベル

In libguestfs E<ge> 1.20, you can give a label to a disk when you add it,
using the optional C<label> parameter to L</guestfs_add_drive_opts>.  (Note
that disk labels are different from and not related to filesystem labels).

Not all versions of libguestfs support setting a disk label, and when it is
supported, it is limited to 20 ASCII characters C<[a-zA-Z]>.

When you add a disk with a label, it can either be addressed using
F</dev/sd*>, or using F</dev/disk/guestfs/I<label>>.  Partitions on the disk
can be addressed using F</dev/disk/guestfs/I<label>I<partnum>>.

Listing devices (L</guestfs_list_devices>) and partitions
(L</guestfs_list_partitions>) returns the block device names.  However you
can use L</guestfs_list_disk_labels> to map disk labels to block device and
partition names.

=head2 NULL DISKS

When adding a disk using, eg., L</guestfs_add_drive>, you can set the
filename to C<"/dev/null">.  This string is treated specially by libguestfs,
causing it to add a "null disk".

A null disk has the following properties:

=over 4

=item *

A null disk will appear as a normal device, eg. in calls to
L</guestfs_list_devices>.

=item *

You may add C<"/dev/null"> multiple times.

=item *

You should not try to access a null disk in any way.  For example, you
shouldn't try to read it or mount it.

=back

Null disks are used for three main purposes:

=over 4

=item 1.

Performance testing of libguestfs (see L<guestfs-performance(1)>).

=item 2.

The internal test suite.

=item 3.

If you want to use libguestfs APIs that don’t refer to disks, since
libguestfs requires that at least one disk is added, you should add a null
disk.

たとえば、機能が利用可能であるかを確認するために、このようなコードを使用します:

 guestfs_h *g;
 char **groups = [ "btrfs", NULL ];
 
 g = guestfs_create ();
 guestfs_add_drive (g, "/dev/null");
 guestfs_launch (g);
 if (guestfs_available (g, groups) == 0) {
   // group(s) are available
 } else {
   // group(s) are not available
 }
 guestfs_close (g);

=back

=head2 DISK IMAGE FORMATS

Virtual disks come in a variety of formats.  Some common formats are listed
below.

Note that libguestfs itself is not responsible for handling the disk format:
this is done using L<qemu(1)>.  If support for a particular format is
missing or broken, this has to be fixed in qemu.

=head3 COMMON VIRTUAL DISK IMAGE FORMATS

=over 4

=item I<raw>

Raw format is simply a dump of the sequential bytes of the virtual hard
disk.  There is no header, container, compression or processing of any sort.

Since raw format requires no translation to read or write, it is both fast
and very well supported by qemu and all other hypervisors.  You can consider
it to be a universal format that any hypervisor can access.

Raw format files are not compressed and so take up the full space of the
original disk image even when they are empty.  A variation (on Linux/Unix at
least) is to not store ranges of all-zero bytes by storing the file as a
sparse file.  This "variant format" is sometimes called I<raw sparse>.  Many
utilities, including L<virt-sparsify(1)>, can make raw disk images sparse.

=item I<qcow2>

Qcow2 is the native disk image format used by qemu.  Internally it uses a
two-level directory structure so that only blocks containing data are stored
in the file.  It also has many other features such as compression, snapshots
and backing files.

There are at least two distinct variants of this format, although qemu (and
hence libguestfs) handles both transparently to the user.

=item I<vmdk>

VMDK is VMware’s native disk image format.  There are many variations.
Modern qemu (hence libguestfs) supports most variations, but you should be
aware that older versions of qemu had some very bad data-corrupting bugs in
this area.

Note that VMware ESX exposes files with the name F<guest-flat.vmdk>.  These
are not VMDK.  They are raw format files which happen to have a C<.vmdk>
extension.

=item I<vdi>

VDI is VirtualBox’s native disk image format.  Qemu (hence libguestfs)  has
generally good support for this.

=item I<vpc>

=item I<vhd>

VPC (旧) と VHD (新) は Microsoft (および、以前の Connectix) Virtual PC および Hyper-V
のネイティブなディスクイメージ形式です。

=item 推奨されない形式

The following formats are obsolete and should not be used: I<qcow> (aka
I<qcow1>), I<cow>, I<bochs>.

=back

=head3 DETECTING THE FORMAT OF A DISK IMAGE

Firstly note there is a security issue with auto-detecting the format of a
disk image.  It may or may not apply in your use case.  Read
L</CVE-2010-3851> below.

Libguestfs offers an API to get the format of a disk image
(L</guestfs_disk_format>), and it is safest to use this.

I<Don’t> be tempted to try parsing the text / human-readable output of
C<qemu-img> since it cannot be parsed reliably and securely.  Also do not
use the C<file> command since the output of that changes over time.

=head1 CONNECTION MANAGEMENT

=head2 guestfs_h *

C<guestfs_h> is the opaque type representing a connection handle.  Create a
handle by calling L</guestfs_create> or L</guestfs_create_flags>.  Call
L</guestfs_close> to free the handle and release all resources used.

For information on using multiple handles and threads, see the section
L</MULTIPLE HANDLES AND MULTIPLE THREADS> above.

=head2 guestfs_create

 guestfs_h *guestfs_create (void);

接続ハンドルを作成します。

On success this returns a non-NULL pointer to a handle.  On error it returns
NULL.

You have to "configure" the handle after creating it.  This includes calling
L</guestfs_add_drive_opts> (or one of the equivalent calls) on the handle at
least once.

ハンドルを設定後、 L</guestfs_launch> を呼び出す必要があります。

You may also want to configure error handling for the handle.  See the
L</ERROR HANDLING> section below.

=head2 guestfs_create_flags

 guestfs_h *guestfs_create_flags (unsigned flags [, ...]);

Create a connection handle, supplying extra flags and extra arguments to
control how the handle is created.

On success this returns a non-NULL pointer to a handle.  On error it returns
NULL.

L</guestfs_create> is equivalent to calling C<guestfs_create_flags(0)>.

The following flags may be logically ORed together.  (Currently no extra
arguments are used).

=over 4

=item C<GUESTFS_CREATE_NO_ENVIRONMENT>

Don’t parse any environment variables (such as C<LIBGUESTFS_DEBUG> etc).

You can call L</guestfs_parse_environment> or
L</guestfs_parse_environment_list> afterwards to parse environment
variables.  Alternately, I<don't> call these functions if you want the
handle to be unaffected by environment variables.  See the example below.

The default (if this flag is not given) is to implicitly call
L</guestfs_parse_environment>.

=item C<GUESTFS_CREATE_NO_CLOSE_ON_EXIT>

Don’t try to close the handle in an L<atexit(3)> handler if the program
exits without explicitly closing the handle.

The default (if this flag is not given) is to install such an atexit
handler.

=back

=head3 C<GUESTFS_CREATE_NO_ENVIRONMENT> の使用法

You might use C<GUESTFS_CREATE_NO_ENVIRONMENT> and an explicit call to
L</guestfs_parse_environment> like this:

 guestfs_h *g;
 int r;
 
 g = guestfs_create_flags (GUESTFS_CREATE_NO_ENVIRONMENT);
 if (!g) {
   perror ("guestfs_create_flags");
   exit (EXIT_FAILURE);
 }
 r = guestfs_parse_environment (g);
 if (r == -1)
   exit (EXIT_FAILURE);

Or to create a handle which is unaffected by environment variables, omit the
call to C<guestfs_parse_environment> from the above code.

The above code has another advantage which is that any errors from parsing
the environment are passed through the error handler, whereas
C<guestfs_create> prints errors on stderr and ignores them.

=head2 guestfs_close

 void guestfs_close (guestfs_h *g);

This closes the connection handle and frees up all resources used.  If a
close callback was set on the handle, then it is called.

ハンドルを閉じる正しい方法は次のとおりです:

 if (guestfs_shutdown (g) == -1) {
   /* ここで書き込みエラーを処理する */
 }
 guestfs_close (g);

L</guestfs_shutdown> は以下の B<すべて> が成り立つ場合のみ必要です:

=over 4

=item 1

一つ以上のディスクを読み書きモードで追加した、I<かつ>

=item 2

guestfs_launch が呼び出された、I<かつ>

=item 3

何か変更を実施した、I<かつ>

=item 4

you have a way to handle write errors (eg. by exiting with an error code or
reporting something to the user).

=back

=head1 エラー処理

API 関数はエラーを返します。たとえば、ほとんどすべての C<int> を返す関数はエラーを意味するために C<-1> を返します。

エラーに関する追加の情報が利用可能です: 失敗したものがシステムコールならば、エラーメッセージ文字列およびオプションのエラー番号（errno）です。

You can get at the additional information about the last error on the handle
by calling L</guestfs_last_error>, L</guestfs_last_errno>, and/or by setting
up an error handler with L</guestfs_set_error_handler>.

When the handle is created, a default error handler is installed which
prints the error message string to C<stderr>.  For small short-running
command line programs it is sufficient to do:

 if (guestfs_launch (g) == -1)
   exit (EXIT_FAILURE);

since the default error handler will ensure that an error message has been
printed to C<stderr> before the program exits.

For other programs the caller will almost certainly want to install an
alternate error handler or do error handling in-line as in the example
below.  The non-C language bindings all install NULL error handlers and turn
errors into exceptions using code similar to this:

 const char *msg;
 int errnum;
 
 /* これは標準エラーにエラーを表示するときの
    デフォルトの動作を無効化します。 */
 guestfs_set_error_handler (g, NULL, NULL);
 
 if (guestfs_launch (g) == -1) {
   /* エラーメッセージを検査する、表示する、例外を投げるなど */
   msg = guestfs_last_error (g);
   errnum = guestfs_last_errno (g);
 
   fprintf (stderr, "%s", msg);
   if (errnum != 0)
     fprintf (stderr, ": %s", strerror (errnum));
   fprintf (stderr, "\n");
 
   /* ... */
 }

L</guestfs_create> returns C<NULL> if the handle cannot be created, and
because there is no handle if this happens there is no way to get additional
error information.  Since libguestfs E<ge> 1.20, you can use
L</guestfs_create_flags> to properly deal with errors during handle
creation, although the vast majority of programs can continue to use
L</guestfs_create> and not worry about this situation.

Out of memory errors are handled differently.  The default action is to call
L<abort(3)>.  If this is undesirable, then you can set a handler using
L</guestfs_set_out_of_memory_handler>.

=head2 guestfs_last_error

 const char *guestfs_last_error (guestfs_h *g);

This returns the last error message that happened on C<g>.  If there has not
been an error since the handle was created, then this returns C<NULL>.

Note the returned string does I<not> have a newline character at the end.
Most error messages are single lines.  Some are split over multiple lines
and contain C<\n> characters within the string but not at the end.

The lifetime of the returned string is until the next error occurs on the
same handle, or L</guestfs_close> is called.  If you need to keep it longer,
copy it.

=head2 guestfs_last_errno

 int guestfs_last_errno (guestfs_h *g);

これは C<g> において発生した最後のエラー番号（errno）を返します。

もし成功すると、0 以外のエラー番号の整数が返されます。

In many cases the special errno C<ENOTSUP> is returned if you tried to call
a function or use a feature which is not supported.

If no error number is available, this returns 0.  This call can return 0 in
three situations:

=over 4

=item 1.

ハンドルにおいて何もエラーがありませんでした。

=item 2.

エラーがありましたが、エラー番号に意味がありませんでした。エラーがシステムコールの失敗により発生しましたが、何か他の理由による場合に対応します。

=item 3.

エラーがシステムコールの失敗により発生しましたが、エラー番号が何らかの理由により捕捉されず返されました。これは通常 libguestfs
のバグを意味します。

=back

Libguestfs tries to convert the errno from inside the appliance into a
corresponding errno for the caller (not entirely trivial: the appliance
might be running a completely different operating system from the library
and error numbers are not standardized across Un*xen).  If this could not be
done, then the error is translated to C<EINVAL>.  In practice this should
only happen in very rare circumstances.

=head2 guestfs_set_error_handler

 typedef void (*guestfs_error_handler_cb) (guestfs_h *g,
                                           void *opaque,
                                           const char *msg);
 void guestfs_set_error_handler (guestfs_h *g,
                                 guestfs_error_handler_cb cb,
                                 void *opaque);

The callback C<cb> will be called if there is an error.  The parameters
passed to the callback are an opaque data pointer and the error message
string.

C<errno> is not passed to the callback.  To get that the callback must call
L</guestfs_last_errno>.

Note that the message string C<msg> is freed as soon as the callback
function returns, so if you want to stash it somewhere you must make your
own copy.

標準のハンドラーは C<stderr> にメッセージを表示します。

C<cb> を C<NULL> に設定すると、 I<no> ハンドラーが呼び出されます。

=head2 guestfs_get_error_handler

 guestfs_error_handler_cb guestfs_get_error_handler (guestfs_h *g,
                                                     void **opaque_rtn);

現在のエラーハンドラのコールバックを返します。

=head2 guestfs_push_error_handler

 void guestfs_push_error_handler (guestfs_h *g,
                                  guestfs_error_handler_cb cb,
                                  void *opaque);

This is the same as L</guestfs_set_error_handler>, except that the old error
handler is stashed away in a stack inside the handle.  You can restore the
previous error handler by calling L</guestfs_pop_error_handler>.

Use the following code to temporarily disable errors around a function:

 guestfs_push_error_handler (g, NULL, NULL);
 guestfs_mkdir (g, "/foo"); /* We don't care if this fails. */
 guestfs_pop_error_handler (g);

=head2 guestfs_pop_error_handler

 void guestfs_pop_error_handler (guestfs_h *g);

Restore the previous error handler (see L</guestfs_push_error_handler>).

If you pop the stack too many times, then the default error handler is
restored.

=head2 guestfs_set_out_of_memory_handler

 typedef void (*guestfs_abort_cb) (void);
 void guestfs_set_out_of_memory_handler (guestfs_h *g,
                                         guestfs_abort_cb);

メモリー不足になると、コールバック C<cb> が呼び出されます。 I<このコールバックは戻ってこない可能性があることに注意してください>。

デフォルトでは L<abort(3)> を呼び出します。

You cannot set C<cb> to C<NULL>.  You can’t ignore out of memory situations.

=head2 guestfs_get_out_of_memory_handler

 guestfs_abort_fn guestfs_get_out_of_memory_handler (guestfs_h *g);

アウトオブメモリーハンドラーを返します。

=head1 API 呼び出し

__ACTIONS__

=head1 構造

__STRUCTS__

=head1 可用性

=head2 アプライアンスの機能のグループ

I<この関数は推奨されません。> 新しいコードでは、代わりに L</part_add> を使用してください。

__AVAILABILITY__

=head2 利用可能なファイルシステム

The L</guestfs_filesystem_available> call tests whether a filesystem type is
supported by the appliance kernel.

This is mainly useful as a negative test.  If this returns true, it doesn't
mean that a particular filesystem can be mounted, since filesystems can fail
for other reasons such as it being a later version of the filesystem, or
having incompatible features.

=head2 guestfish がサポートするコマンド

In L<guestfish(3)> there is a handy interactive command C<supported> which
prints out the available groups and whether they are supported by this build
of libguestfs.  Note however that you have to do C<run> first.

=head2 SINGLE CALLS AT COMPILE TIME

バージョン 1.5.8 から C<E<lt>guestfs.hE<gt>> に定義されたシンボルの C API
関数があります。次のようなものがあります:

 #define GUESTFS_HAVE_DD 1

L</guestfs_dd> が利用可能な場合。

Before version 1.5.8, if you needed to test whether a single libguestfs
function is available at compile time, we recommended using build tools such
as autoconf or cmake.  For example in autotools you could use:

 AC_CHECK_LIB([guestfs],[guestfs_create])
 AC_CHECK_FUNCS([guestfs_dd])

which would result in C<HAVE_GUESTFS_DD> being either defined or not defined
in your program.

=head2 SINGLE CALLS AT RUN TIME

I<この関数は推奨されません。> 新しいコードでは、代わりに L</part_list> を使用してください。

I<この関数は推奨されません。> 新しいコードでは、代わりに L</write> を使用してください。

 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <dlfcn.h>
 #include <guestfs.h>
 
 main ()
 {
 #ifdef GUESTFS_HAVE_DD
   void *dl;
   int has_function;
 
   /* guestfs_dd 関数が本当に利用可能かを確認します。 */
   dl = dlopen (NULL, RTLD_LAZY);
   if (!dl) {
     fprintf (stderr, "dlopen: %s\n", dlerror ());
     exit (EXIT_FAILURE);
   }
   has_function = dlsym (dl, "guestfs_dd") != NULL;
   dlclose (dl);
 
   if (!has_function)
     printf ("この libguestfs.so は guestfs_dd 関数がありません\n");
   else {
     printf ("この libguestfs.so は guestfs_dd 関数があります\n");
     /* Now it's safe to call
     guestfs_dd (g, "foo", "bar");
     */
   }
 #else
   printf ("guestfs_dd 関数がコンパイル時に見つかりませんでした\n");
 #endif
  }

You may think the above is an awful lot of hassle, and it is.  There are
other ways outside of the C linking system to ensure that this kind of
incompatibility never arises, such as using package versioning:

 Requires: libguestfs >= 1.0.80

=head1 CALLS WITH OPTIONAL ARGUMENTS

A recent feature of the API is the introduction of calls which take optional
arguments.  In C these are declared 3 ways.  The main way is as a call which
takes variable arguments (ie. C<...>), as in this example:

 int guestfs_add_drive_opts (guestfs_h *g, const char *filename, ...);

Call this with a list of optional arguments, terminated by C<-1>.  So to
call with no optional arguments specified:

 guestfs_add_drive_opts (g, filename, -1);

単一の引数の場合:

 guestfs_add_drive_opts (g, filename,
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
                         -1);

2つの引数の場合:

 guestfs_add_drive_opts (g, filename,
                         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "qcow2",
                         GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
                         -1);

and so forth.  Don’t forget the terminating C<-1> otherwise Bad Things will
happen!

=head2 USING va_list FOR OPTIONAL ARGUMENTS

I<この関数は推奨されません。> 新しいコードでは、代わりに L</guestfs_add_drive_opts> を使用してください。

 int guestfs_add_drive_opts_va (guestfs_h *g, const char *filename,
                                va_list args);

=head2 オプション引数の構築

The third variant is useful where you need to construct these calls.  You
pass in a structure where you fill in the optional fields.  The structure
has a bitmask as the first element which you must set to indicate which
fields you have filled in.  For our example function the structure and call
are declared:

 struct guestfs_add_drive_opts_argv {
   uint64_t bitmask;
   int readonly;
   const char *format;
   /* ... */
 };
 int guestfs_add_drive_opts_argv (guestfs_h *g, const char *filename,
              const struct guestfs_add_drive_opts_argv *optargs);

次のように呼び出すことができます。

 struct guestfs_add_drive_opts_argv optargs = {
   .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK |
              GUESTFS_ADD_DRIVE_OPTS_FORMAT_BITMASK,
   .readonly = 1,
   .format = "qcow2"
 };
 
 guestfs_add_drive_opts_argv (g, filename, &optargs);

注:

=over 4

=item *

The C<_BITMASK> suffix on each option name when specifying the bitmask.

=item *

You do not need to fill in all fields of the structure.

=item *

There must be a one-to-one correspondence between fields of the structure
that are filled in, and bits set in the bitmask.

=back

=head2 OPTIONAL ARGUMENTS IN OTHER LANGUAGES

In other languages, optional arguments are expressed in the way that is
natural for that language.  We refer you to the language-specific
documentation for more details on that.

guestfish は L<guestfish(1)/OPTIONAL ARGUMENTS> を参照してください。

=head1 イベント

=head2 SETTING CALLBACKS TO HANDLE EVENTS

B<Note:> This section documents the generic event mechanism introduced in
libguestfs 1.10, which you should use in new code if possible.  The old
functions C<guestfs_set_log_message_callback>,
C<guestfs_set_subprocess_quit_callback>,
C<guestfs_set_launch_done_callback>, C<guestfs_set_close_callback> and
C<guestfs_set_progress_callback> are no longer documented in this manual
page.  Because of the ABI guarantee, the old functions continue to work.

Handles generate events when certain things happen, such as log messages
being generated, progress messages during long-running operations, or the
handle being closed.  The API calls described below let you register a
callback to be called when events happen.  You can register multiple
callbacks (for the same, different or overlapping sets of events), and
individually remove callbacks.  If callbacks are not removed, then they
remain in force until the handle is closed.

In the current implementation, events are only generated synchronously: that
means that events (and hence callbacks) can only happen while you are in the
middle of making another libguestfs call.  The callback is called in the
same thread.

Events may contain a payload, usually nothing (void), an array of 64 bit
unsigned integers, or a message buffer.  Payloads are discussed later on.

=head2 イベントのクラス

=over 4

=item GUESTFS_EVENT_CLOSE (ペイロード形式: void)

The callback function will be called while the handle is being closed
(synchronously from L</guestfs_close>).

I<この関数は推奨されません。> 新しいコードでは、代わりに L</guestfs_fallocate64> を使用してください。

If no callback is registered: the handle is closed without any callback
being invoked.

=item GUESTFS_EVENT_SUBPROCESS_QUIT (ペイロード形式: void)

The callback function will be called when the child process quits, either
asynchronously or if killed by L</guestfs_kill_subprocess>.  (This
corresponds to a transition from any state to the CONFIG state).

If no callback is registered: the event is ignored.

=item GUESTFS_EVENT_LAUNCH_DONE (ペイロード形式: void)

The callback function will be called when the child process becomes ready
first time after it has been launched.  (This corresponds to a transition
from LAUNCHING to the READY state).

If no callback is registered: the event is ignored.

=item GUESTFS_EVENT_PROGRESS (ペイロード形式: 4 x uint64_t の配列)

Some long-running operations can generate progress messages.  If this
callback is registered, then it will be called each time a progress message
is generated (usually two seconds after the operation started, and three
times per second thereafter until it completes, although the frequency may
change in future versions).

The callback receives in the payload four unsigned 64 bit numbers which are
(in order): C<proc_nr>, C<serial>, C<position>, C<total>.

The units of C<total> are not defined, although for some operations C<total>
may relate in some way to the amount of data to be transferred (eg. in bytes
or megabytes), and C<position> may be the portion which has been
transferred.

The only defined and stable parts of the API are:

=over 4

=item *

The callback can display to the user some type of progress bar or indicator
which shows the ratio of C<position>:C<total>.

=item *

0 E<lt>= C<position> E<lt>= C<total>

=item *

If any progress notification is sent during a call, then a final progress
notification is always sent when C<position> = C<total> (I<unless> the call
fails with an error).

This is to simplify caller code, so callers can easily set the progress
indicator to "100%" at the end of the operation, without requiring special
code to detect this case.

=item *

For some calls we are unable to estimate the progress of the call, but we
can still generate progress messages to indicate activity.  This is known as
"pulse mode", and is directly supported by certain progress bar
implementations (eg. GtkProgressBar).

For these calls, zero or more progress messages are generated with
C<position = 0> and C<total = 1>, followed by a final message with
C<position = total = 1>.

As noted above, if the call fails with an error then the final message may
not be generated.

=back

The callback also receives the procedure number (C<proc_nr>) and serial
number (C<serial>) of the call.  These are only useful for debugging
protocol issues, and the callback can normally ignore them.  The callback
may want to print these numbers in error messages or debugging messages.

If no callback is registered: progress messages are discarded.

=item GUESTFS_EVENT_APPLIANCE (ペイロード形式: メッセージバッファー)

The callback function is called whenever a log message is generated by qemu,
the appliance kernel, guestfsd (daemon), or utility programs.

If the verbose flag (L</guestfs_set_verbose>) is set before launch
(L</guestfs_launch>) then additional debug messages are generated.

If no callback is registered: the messages are discarded unless the verbose
flag is set in which case they are sent to stderr.  You can override the
printing of verbose messages to stderr by setting up a callback.

=item GUESTFS_EVENT_LIBRARY (payload type: message buffer)

The callback function is called whenever a log message is generated by the
library part of libguestfs.

If the verbose flag (L</guestfs_set_verbose>) is set then additional debug
messages are generated.

If no callback is registered: the messages are discarded unless the verbose
flag is set in which case they are sent to stderr.  You can override the
printing of verbose messages to stderr by setting up a callback.

=item GUESTFS_EVENT_WARNING (payload type: message buffer)

The callback function is called whenever a warning message is generated by
the library part of libguestfs.

If no callback is registered: the messages are printed to stderr.  You can
override the printing of warning messages to stderr by setting up a
callback.

=item GUESTFS_EVENT_TRACE (ペイロード形式: メッセージバッファー)

The callback function is called whenever a trace message is generated.  This
only applies if the trace flag (L</guestfs_set_trace>) is set.

If no callback is registered: the messages are sent to stderr.  You can
override the printing of trace messages to stderr by setting up a callback.

=item GUESTFS_EVENT_ENTER (payload type: function name)

The callback function is called whenever a libguestfs function is entered.

The payload is a string which contains the name of the function that we are
entering (not including C<guestfs_> prefix).

Note that libguestfs functions can call themselves, so you may see many
events from a single call.  A few libguestfs functions do not generate this
event.

If no callback is registered: the event is ignored.

=item GUESTFS_EVENT_LIBVIRT_AUTH (payload type: libvirt URI)

For any API function that opens a libvirt connection, this event may be
generated to indicate that libvirt demands authentication information.  See
L</LIBVIRT AUTHENTICATION> below.

If no callback is registered: C<virConnectAuthPtrDefault> is used (suitable
for command-line programs only).

=back

=head2 イベント API

=head3 guestfs_set_event_callback

 int guestfs_set_event_callback (guestfs_h *g,
                                 guestfs_event_callback cb,
                                 uint64_t event_bitmask,
                                 int flags,
                                 void *opaque);

This function registers a callback (C<cb>) for all event classes in the
C<event_bitmask>.

For example, to register for all log message events, you could call this
function with the bitmask
C<GUESTFS_EVENT_APPLIANCE|GUESTFS_EVENT_LIBRARY|GUESTFS_EVENT_WARNING>.  To
register a single callback for all possible classes of events, use
C<GUESTFS_EVENT_ALL>.

C<flags> should always be passed as 0.

C<opaque> is an opaque pointer which is passed to the callback.  You can use
it for any purpose.

The return value is the event handle (an integer) which you can use to
delete the callback (see below).

If there is an error, this function returns C<-1>, and sets the error in the
handle in the usual way (see L</guestfs_last_error> etc.)

Callbacks remain in effect until they are deleted, or until the handle is
closed.

In the case where multiple callbacks are registered for a particular event
class, all of the callbacks are called.  The order in which multiple
callbacks are called is not defined.

=head3 guestfs_delete_event_callback

 void guestfs_delete_event_callback (guestfs_h *g, int event_handle);

Delete a callback that was previously registered.  C<event_handle> should be
the integer that was returned by a previous call to
C<guestfs_set_event_callback> on the same handle.

=head3 guestfs_event_to_string

 char *guestfs_event_to_string (uint64_t event);

C<event> is either a single event or a bitmask of events.  This returns a
string representation (useful for debugging or printing events).

A single event is returned as the name in lower case, eg. C<"close">.

A bitmask of several events is returned as a comma-separated list,
eg. C<"close,progress">.

If zero is passed, then the empty string C<""> is returned.

On success this returns a string.  On error it returns NULL and sets
C<errno>.

The returned string must be freed by the caller.

=head3 guestfs_event_callback

 typedef void (*guestfs_event_callback) (
                  guestfs_h *g,
                  void *opaque,
                  uint64_t event,
                  int event_handle,
                  int flags,
                  const char *buf, size_t buf_len,
                  const uint64_t *array, size_t array_len);

This is the type of the event callback function that you have to provide.

The basic parameters are: the handle (C<g>), the opaque user pointer
(C<opaque>), the event class (eg. C<GUESTFS_EVENT_PROGRESS>), the event
handle, and C<flags> which in the current API you should ignore.

The remaining parameters contain the event payload (if any).  Each event may
contain a payload, which usually relates to the event class, but for future
proofing your code should be written to handle any payload for any event
class.

C<buf> and C<buf_len> contain a message buffer (if C<buf_len == 0>, then
there is no message buffer).  Note that this message buffer can contain
arbitrary 8 bit data, including NUL bytes.

C<array> and C<array_len> is an array of 64 bit unsigned integers.  At the
moment this is only used for progress messages.

=head2 EXAMPLE: CAPTURING LOG MESSAGES

A working program demonstrating this can be found in
F<examples/debug-logging.c> in the source of libguestfs.

One motivation for the generic event API was to allow GUI programs to
capture debug and other messages.  In libguestfs E<le> 1.8 these were sent
unconditionally to C<stderr>.

Events associated with log messages are: C<GUESTFS_EVENT_LIBRARY>,
C<GUESTFS_EVENT_APPLIANCE>, C<GUESTFS_EVENT_WARNING> and
C<GUESTFS_EVENT_TRACE>.  (Note that error messages are not events; you must
capture error messages separately).

Programs have to set up a callback to capture the classes of events of
interest:

 int eh =
   guestfs_set_event_callback
     (g, message_callback,
      GUESTFS_EVENT_LIBRARY | GUESTFS_EVENT_APPLIANCE |
      GUESTFS_EVENT_WARNING | GUESTFS_EVENT_TRACE,
      0, NULL) == -1)
 if (eh == -1) {
   // handle error in the usual way
 }

The callback can then direct messages to the appropriate place.  In this
example, messages are directed to syslog:

 static void
 message_callback (
         guestfs_h *g,
         void *opaque,
         uint64_t event,
         int event_handle,
         int flags,
         const char *buf, size_t buf_len,
         const uint64_t *array, size_t array_len)
 {
   const int priority = LOG_USER|LOG_INFO;
   if (buf_len > 0)
     syslog (priority, "event 0x%lx: %s", event, buf);
 }

=head2 libvirt 認証

Some libguestfs API calls can open libvirt connections.  Currently the only
ones are L</guestfs_add_domain>; and L</guestfs_launch> if the libvirt
backend has been selected.  Libvirt connections may require authentication,
for example if they need to access a remote server or to access root
services from non-root.  Libvirt authentication happens via a callback
mechanism, see
L<http://libvirt.org/guide/html/Application_Development_Guide-Connections.html>

You may provide libvirt authentication data by registering a callback for
events of type C<GUESTFS_EVENT_LIBVIRT_AUTH>.

If no such event is registered, then libguestfs uses a libvirt function that
provides command-line prompts (C<virConnectAuthPtrDefault>).  This is only
suitable for command-line libguestfs programs.

To provide authentication, first call
L</guestfs_set_libvirt_supported_credentials> with the list of credentials
your program knows how to provide.  Second, register a callback for the
C<GUESTFS_EVENT_LIBVIRT_AUTH> event.  The event handler will be called when
libvirt is requesting authentication information.

In the event handler, call L</guestfs_get_libvirt_requested_credentials> to
get a list of the credentials that libvirt is asking for.  You then need to
ask (eg. the user) for each credential, and call
L</guestfs_set_libvirt_requested_credential> with the answer.  Note that for
each credential, additional information may be available via the calls
L</guestfs_get_libvirt_requested_credential_prompt>,
L</guestfs_get_libvirt_requested_credential_challenge> or
L</guestfs_get_libvirt_requested_credential_defresult>.

The example program below should make this clearer.

There is also a more substantial working example program supplied with the
libguestfs sources, called F<libvirt-auth.c>.

 main ()
 {
   guestfs_h *g;
   char *creds[] = { "authname", "passphrase", NULL };
   int r, eh;
 
   g = guestfs_create ();
   if (!g) exit (EXIT_FAILURE);
 
   /* プログラムがサポートするクレデンシャルを libvirt に伝える。 */
   r = guestfs_set_libvirt_supported_credentials (g, creds);
   if (r == -1)
     exit (EXIT_FAILURE);
 
   /* イベントハンドラーをセットアップする。 */
   eh = guestfs_set_event_callback (
       g, do_auth,
       GUESTFS_EVENT_LIBVIRT_AUTH, 0, NULL);
   if (eh == -1)
     exit (EXIT_FAILURE);
 
   /* An example of a call that may ask for credentials. */
   r = guestfs_add_domain (
       g, "dom",
       GUESTFS_ADD_DOMAIN_LIBVIRTURI, "qemu:///system",
       -1);
   if (r == -1)
     exit (EXIT_FAILURE);
 
   exit (EXIT_SUCCESS);
 }
 
 static void
 do_auth (guestfs_h *g,
          void *opaque,
          uint64_t event,
          int event_handle,
          int flags,
          const char *buf, size_t buf_len,
          const uint64_t *array, size_t array_len)
 {
   char **creds;
   size_t i;
   char *prompt;
   char *reply;
   size_t replylen;
   int r;
 
   // buf will be the libvirt URI.  buf_len may be ignored.
   printf ("Authentication required for libvirt conn '%s'\n",
           buf);
 
   // Ask libguestfs what credentials libvirt is demanding.
   creds = guestfs_get_libvirt_requested_credentials (g);
   if (creds == NULL)
     exit (EXIT_FAILURE);
 
   // Now ask the user for answers.
   for (i = 0; creds[i] != NULL; ++i)
   {
     if (strcmp (creds[i], "authname") == 0 ||
         strcmp (creds[i], "passphrase") == 0)
     {
       prompt =
         guestfs_get_libvirt_requested_credential_prompt (g, i);
       if (prompt && strcmp (prompt, "") != 0)
         printf ("%s: ", prompt);
       free (prompt);
 
       // Some code here to ask for the credential.
       // ...
       // Put the reply in 'reply', length 'replylen' (bytes).
 
      r = guestfs_set_libvirt_requested_credential (g, i,
          reply, replylen);
      if (r == -1)
        exit (EXIT_FAILURE);
     }
 
     free (creds[i]);
   }
 
   free (creds);
 }

=head1 CANCELLING LONG TRANSFERS

Some operations can be cancelled by the caller while they are in progress.
Currently only operations that involve uploading or downloading data can be
cancelled (technically: operations that have C<FileIn> or C<FileOut>
parameters in the generator).

To cancel the transfer, call L</guestfs_user_cancel>.  For more information,
read the description of L</guestfs_user_cancel>.

=head1 プライベートデータ領域

You can attach named pieces of private data to the libguestfs handle, fetch
them by name, and walk over them, for the lifetime of the handle.  This is
called the private data area and is only available from the C API.

データの名前付き部分を接続するには、以下の呼び出しを使用します:

 void guestfs_set_private (guestfs_h *g, const char *key, void *data);

C<key> is the name to associate with this data, and C<data> is an arbitrary
pointer (which can be C<NULL>).  Any previous item with the same key is
overwritten.

You can use any C<key> string you want, but avoid keys beginning with an
underscore character (libguestfs uses those for its own internal purposes,
such as implementing language bindings).  It is recommended that you prefix
the key with some unique string to avoid collisions with other users.

ポインターを取り出すには、次を使用します:

 void *guestfs_get_private (guestfs_h *g, const char *key);

This function returns C<NULL> if either no data is found associated with
C<key>, or if the user previously set the C<key>’s C<data> pointer to
C<NULL>.

Libguestfs does not try to look at or interpret the C<data> pointer in any
way.  As far as libguestfs is concerned, it need not be a valid pointer at
all.  In particular, libguestfs does I<not> try to free the data when the
handle is closed.  If the data must be freed, then the caller must either
free it before calling L</guestfs_close> or must set up a close callback to
do it (see L</GUESTFS_EVENT_CLOSE>).

To walk over all entries, use these two functions:

 void *guestfs_first_private (guestfs_h *g, const char **key_rtn);

 void *guestfs_next_private (guestfs_h *g, const char **key_rtn);

C<guestfs_first_private> returns the first key, pointer pair ("first" does
not have any particular meaning -- keys are not returned in any defined
order).  A pointer to the key is returned in C<*key_rtn> and the
corresponding data pointer is returned from the function.  C<NULL> is
returned if there are no keys stored in the handle.

C<guestfs_next_private> returns the next key, pointer pair.  The return
value of this function is C<NULL> if there are no further entries to return.

Notes about walking over entries:

=over 4

=item *

You must not call C<guestfs_set_private> while walking over the entries.

=item *

The handle maintains an internal iterator which is reset when you call
C<guestfs_first_private>.  This internal iterator is invalidated when you
call C<guestfs_set_private>.

=item *

If you have set the data pointer associated with a key to C<NULL>, ie:

 guestfs_set_private (g, key, NULL);

then that C<key> is not returned when walking.

=item *

C<*key_rtn> is only valid until the next call to C<guestfs_first_private>,
C<guestfs_next_private> or C<guestfs_set_private>.

=back

The following example code shows how to print all keys and data pointers
that are associated with the handle C<g>:

 const char *key;
 void *data = guestfs_first_private (g, &key);
 while (data != NULL)
   {
     printf ("key = %s, data = %p\n", key, data);
     data = guestfs_next_private (g, &key);
   }

More commonly you are only interested in keys that begin with an
application-specific prefix C<foo_>.  Modify the loop like so:

 const char *key;
 void *data = guestfs_first_private (g, &key);
 while (data != NULL)
   {
     if (strncmp (key, "foo_", strlen ("foo_")) == 0)
       printf ("key = %s, data = %p\n", key, data);
     data = guestfs_next_private (g, &key);
   }

If you need to modify keys while walking, then you have to jump back to the
beginning of the loop.  For example, to delete all keys prefixed with
C<foo_>:

  const char *key;
  void *data;
 again:
  data = guestfs_first_private (g, &key);
  while (data != NULL)
    {
      if (strncmp (key, "foo_", strlen ("foo_")) == 0)
        {
          guestfs_set_private (g, key, NULL);
          /* note that 'key' pointer is now invalid, and so is
             the internal iterator */
          goto again;
        }
      data = guestfs_next_private (g, &key);
    }

Note that the above loop is guaranteed to terminate because the keys are
being deleted, but other manipulations of keys within the loop might not
terminate unless you also maintain an indication of which keys have been
visited.

=head1 SYSTEMTAP

The libguestfs C library can be probed using systemtap or DTrace.  This is
true of any library, not just libguestfs.  However libguestfs also contains
static markers to help in probing internal operations.

You can list all the static markers by doing:

 stap -l 'process("/usr/lib*/libguestfs.so.0")
              .provider("guestfs").mark("*")'

B<Note:> These static markers are I<not> part of the stable API and may
change in future versions.

=head2 SYSTEMTAP SCRIPT EXAMPLE

This script contains examples of displaying both the static markers and some
ordinary C entry points:

 global last;
 
 function display_time () {
       now = gettimeofday_us ();
       delta = 0;
       if (last > 0)
             delta = now - last;
       last = now;
 
       printf ("%d (+%d):", now, delta);
 }
 
 probe begin {
       last = 0;
       printf ("ready\n");
 }
 
 /* Display all calls to static markers. */
 probe process("/usr/lib*/libguestfs.so.0")
           .provider("guestfs").mark("*") ? {
       display_time();
       printf ("\t%s %s\n", $$name, $$parms);
 }
 
 /* guestfs_mkfs* 関数へのすべての呼び出しを一覧表示します。 */
 probe process("/usr/lib*/libguestfs.so.0")
           .function("guestfs_mkfs*") ? {
       display_time();
       printf ("\t%s %s\n", probefunc(), $$parms);
 }

The script above can be saved to F<test.stap> and run using the L<stap(1)>
program.  Note that you either have to be root, or you have to add yourself
to several special stap groups.  Consult the systemtap documentation for
more information.

 # stap /tmp/test.stap
 ready

他の端末において、このように guestfish コマンドを実行します:

 guestfish -N fs

In the first terminal, stap trace output similar to this is shown:

 1318248056692655 (+0):	launch_start
 1318248056692850 (+195):       launch_build_appliance_start
 1318248056818285 (+125435):    launch_build_appliance_end
 1318248056838059 (+19774):     launch_run_qemu
 1318248061071167 (+4233108):   launch_end
 1318248061280324 (+209157):    guestfs_mkfs g=0x1024ab0 fstype=0x46116f device=0x1024e60

=head1 LIBGUESTFS VERSION NUMBERS

Since April 2010, libguestfs has started to make separate development and
stable releases, along with corresponding branches in our git repository.
These separate releases can be identified by version number:

                 偶数は安定版: 1.2.x, 1.4.x, ...
       .-------- 奇数は開発版: 1.3.x, 1.5.x, ...
       |
       v
 1  .  3  .  5
 ^           ^
 |           |
 |           `-------- サブバージョン
 |
 `------ ABI を変更しないので、必ず '1' です

このように "1.3.5" は開発ブランチ "1.3" の 5 番目のアップデートです。

As time passes we cherry pick fixes from the development branch and backport
those into the stable branch, the effect being that the stable branch should
get more stable and less buggy over time.  So the stable releases are ideal
for people who don't need new features but would just like the software to
work.

バックポートする変更に対する私たちの基準は次のとおりです:

=over 4

=item *

Documentation changes which don’t affect any code are backported unless the
documentation refers to a future feature which is not in stable.

=item *

議論の余地がなく、明らかな問題を修正する、十分にテストされたバグ修正はバックポートされます。

=item *

Simple rearrangements of code which shouldn't affect how it works get
backported.  This is so that the code in the two branches doesn't get too
far out of step, allowing us to backport future fixes more easily.

=item *

We I<don’t> backport new features, new APIs, new tools etc, except in one
exceptional case: the new feature is required in order to implement an
important bug fix.

=back

A new stable branch starts when we think the new features in development are
substantial and compelling enough over the current stable branch to warrant
it.  When that happens we create new stable and development versions 1.N.0
and 1.(N+1).0 [N is even].  The new dot-oh release won't necessarily be so
stable at this point, but by backporting fixes from development, that branch
will stabilize over time.

=head1 制限

=head2 プロトコル制限

Internally libguestfs uses a message-based protocol to pass API calls and
their responses to and from a small "appliance" (see L<guestfs-internals(1)>
for plenty more detail about this).  The maximum message size used by the
protocol is slightly less than 4 MB.  For some API calls you may need to be
aware of this limit.  The API calls which may be affected are individually
documented, with a link back to this section of the documentation.

In libguestfs E<lt> 1.19.32, several calls had to encode either their entire
argument list or their entire return value (or sometimes both)  in a single
protocol message, and this gave them an arbitrary limitation on how much
data they could handle.  For example, L</guestfs_cat> could only download a
file if it was less than around 4 MB in size.  In later versions of
libguestfs, some of these limits have been removed.  The APIs which were
previously limited but are now unlimited (except perhaps by available
memory) are listed below.  To find out if a specific API is subject to
protocol limits, check for the warning in the API documentation which links
to this section, and remember to check the version of the documentation that
matches the version of libguestfs you are using.

L</guestfs_cat>, L</guestfs_find>, L</guestfs_read_file>,
L</guestfs_read_lines>, L</guestfs_write>, L</guestfs_write_append>,
L</guestfs_lstatlist>, L</guestfs_lxattrlist>, L</guestfs_readlinklist>,
L</guestfs_ls>.

See also L</UPLOADING> and L</DOWNLOADING> for further information about
copying large amounts of data into or out of a filesystem.

=head2 ディスクの最大数

In libguestfs E<ge> 1.19.7, you can query the maximum number of disks that
may be added by calling L</guestfs_max_disks>.  In earlier versions of
libguestfs (ie. where this call is not available) you should assume the
maximum is 25.

The rest of this section covers implementation details, which could change
in future.

virtio-scsi ディスク (QEMU において利用可能ならば初期値) を使用しているとき、現在の制限は B<255>
個のディスクです。virtio-blk (古い初期値) を使用しているとき、約 B<27>
個のディスクです。しかし、実装の詳細やネットワークが有効化されているかどうかにより、変化する可能性があります。

libguestfs により使用される virtio-scsi はディスクあたり一つのターゲットを使用するよう設定されます。256
個のターゲットが利用可能です。

virtio-blk はディスクあたり 1 仮想 PCI を消費します。PCI は 31
スロットに制限されます。これらのいくつかは他の目的のために使用されます。

一つの仮想ディスクが libguestfs により内部的に使用されます。

Before libguestfs 1.19.7, disk names had to be a single character
(eg. F</dev/sda> through F</dev/sdz>), and since one disk is reserved, that
meant the limit was 25.  This has been fixed in more recent versions.

libguestfs E<ge> 1.20 はディスクの活性挿入をできます。 L</HOTPLUGGING> 参照。

=head2 ディスクあたりの最大パーティション数

virtio はディスクあたりの最大パーティション数を B<15> に制限します。

This is because it reserves 4 bits for the minor device number (thus
F</dev/vda>, and F</dev/vda1> through F</dev/vda15>).

15 よりも多くのパーティションを持つディスクを接続すると、追加のパーティションは libguestfs により無視されます。

=head2 ディスクの最大容量

制限はおそらく 2**63-1 から 2**64-1 バイトの間です。

We have tested block devices up to 1 exabyte (2**60 or
1,152,921,504,606,846,976 bytes) using sparse files backed by an XFS host
filesystem.

Although libguestfs probably does not impose any limit, the underlying host
storage will.  If you store disk images on a host ext4 filesystem, then the
maximum size will be limited by the maximum ext4 file size (currently 16
TB).  If you store disk images as host logical volumes then you are limited
by the maximum size of an LV.

For the hugest disk image files, we recommend using XFS on the host for
storage.

=head2 パーティションの最大容量

The MBR (ie. classic MS-DOS) partitioning scheme uses 32 bit sector
numbers.  Assuming a 512 byte sector size, this means that MBR cannot
address a partition located beyond 2 TB on the disk.

It is recommended that you use GPT partitions on disks which are larger than
this size.  GPT uses 64 bit sector numbers and so can address partitions
which are theoretically larger than the largest disk we could support.

=head2 ファイルシステム、ファイル、ディレクトリーの最大容量

This depends on the filesystem type.  libguestfs itself does not impose any
known limit.  Consult Wikipedia or the filesystem documentation to find out
what these limits are.

=head2 最大アップロード数およびダウンロード数

API 関数 L</guestfs_upload>, L</guestfs_download>, L</guestfs_tar_in>,
L</guestfs_tar_out> および類似のものは、アップロードとダウンロードの数量に制限がありません。

=head2 検査の制限

The inspection code has several arbitrary limits on things like the size of
Windows Registry hive it will read, and the length of product name.  These
are intended to stop a malicious guest from consuming arbitrary amounts of
memory and disk space on the host, and should not be reached in practice.
See the source code for more information.

=head1 ADVANCED MACHINE READABLE OUTPUT

Some of the tools support a I<--machine-readable> option, which is generally
used to make the output more machine friendly, for easier parsing for
example.  By default, this output goes to stdout.

In addition to that, a subset of these tools support an extra string passed
to the I<--machine-readable> option: this string specifies where the
machine-readable output will go.

The possible values are:

=over 4

=item B<file:>F<filename>

The output goes to the specified F<filename>.

=item B<stream:stdout>

The output goes to stdout.  This is basically the same as the default
behaviour of I<--machine-readable> with no parameter, although stdout as
output is specified explicitly.

=item B<stream:stderr>

The output goes to stderr.

=back

=head1 環境変数

=over 4

=item LIBGUESTFS_APPEND

仮想マシンのカーネルに追加のオプションを渡します。

=item LIBGUESTFS_ATTACH_METHOD

This is the old way to set C<LIBGUESTFS_BACKEND>.

=item LIBGUESTFS_BACKEND

Choose the default way to create the appliance.  See L</guestfs_set_backend>
and L</BACKEND>.

=item LIBGUESTFS_BACKEND_SETTINGS

A colon-separated list of backend-specific settings.  See L</BACKEND>,
L</BACKEND SETTINGS>.

=item LIBGUESTFS_CACHEDIR

The location where libguestfs will cache its appliance, when using a
supermin appliance.  The appliance is cached and shared between all handles
which have the same effective user ID.

If C<LIBGUESTFS_CACHEDIR> is not set, then C<TMPDIR> is used.  If C<TMPDIR>
is not set, then F</var/tmp> is used.

See also L</LIBGUESTFS_TMPDIR>, L</guestfs_set_cachedir>.

=item LIBGUESTFS_DEBUG

Set C<LIBGUESTFS_DEBUG=1> to enable verbose messages.  This has the same
effect as calling C<guestfs_set_verbose (g, 1)>.

=item LIBGUESTFS_HV

Set the default hypervisor (usually qemu) binary that libguestfs uses.  If
not set, then the qemu which was found at compile time by the configure
script is used.

上の L</QEMU WRAPPERS> 参照。

=item LIBGUESTFS_MEMSIZE

Set the memory allocated to the qemu process, in megabytes.  For example:

 LIBGUESTFS_MEMSIZE=700

=item LIBGUESTFS_PATH

Set the path that libguestfs uses to search for a supermin appliance.  See
the discussion of paths in section L</PATH> above.

=item LIBGUESTFS_QEMU

This is the old way to set C<LIBGUESTFS_HV>.

=item LIBGUESTFS_TMPDIR

The location where libguestfs will store temporary files used by each
handle.

If C<LIBGUESTFS_TMPDIR> is not set, then C<TMPDIR> is used.  If C<TMPDIR> is
not set, then F</tmp> is used.

See also L</LIBGUESTFS_CACHEDIR>, L</guestfs_set_tmpdir>.

=item LIBGUESTFS_TRACE

コマンドトレースを有効にするには C<LIBGUESTFS_TRACE=1> を設定します。これは C<guestfs_set_trace (g,
1)> の呼び出しと同じ効果があります。

=item パス

Libguestfs may run some external programs, and relies on C<$PATH> being set
to a reasonable value.  If using the libvirt backend, libvirt will not work
at all unless C<$PATH> contains the path of qemu/KVM.  Note that PHP by
default removes C<$PATH> from the environment which tends to break
everything.

=item SUPERMIN_KERNEL

=item SUPERMIN_KERNEL_VERSION

=item SUPERMIN_MODULES

These three environment variables allow the kernel that libguestfs uses in
the appliance to be selected.  If C<$SUPERMIN_KERNEL> is not set, then the
most recent host kernel is chosen.  For more information about kernel
selection, see L<supermin(1)>.

=item TMPDIR

See L</LIBGUESTFS_CACHEDIR>, L</LIBGUESTFS_TMPDIR>.

=item XDG_RUNTIME_DIR

This directory represents a user-specific directory for storing
non-essential runtime files.

If it is set, then is used to store temporary sockets.  Otherwise, F</tmp>
is used.

See also L</get-sockdir>,
L<http://www.freedesktop.org/wiki/Specifications/basedir-spec/>.

=back

=head1 関連項目

Examples written in C: L<guestfs-examples(3)>.

Language bindings: L<guestfs-erlang(3)>, L<guestfs-gobject(3)>,
L<guestfs-golang(3)>, L<guestfs-java(3)>, L<guestfs-lua(3)>,
L<guestfs-ocaml(3)>, L<guestfs-perl(3)>, L<guestfs-python(3)>,
L<guestfs-ruby(3)>.

Tools: L<guestfish(1)>, L<guestmount(1)>, L<virt-alignment-scan(1)>,
L<virt-builder(1)>, L<virt-builder-repository(1)>, L<virt-cat(1)>,
L<virt-copy-in(1)>, L<virt-copy-out(1)>, L<virt-customize(1)>,
L<virt-df(1)>, L<virt-diff(1)>, L<virt-edit(1)>, L<virt-filesystems(1)>,
L<virt-format(1)>, L<virt-inspector(1)>, L<virt-list-filesystems(1)>,
L<virt-list-partitions(1)>, L<virt-log(1)>, L<virt-ls(1)>,
L<virt-make-fs(1)>, L<virt-p2v(1)>, L<virt-rescue(1)>, L<virt-resize(1)>,
L<virt-sparsify(1)>, L<virt-sysprep(1)>, L<virt-tail(1)>, L<virt-tar(1)>,
L<virt-tar-in(1)>, L<virt-tar-out(1)>, L<virt-v2v(1)>, L<virt-win-reg(1)>.

Other libguestfs topics: L<guestfs-building(1)>, L<guestfs-faq(1)>,
L<guestfs-hacking(1)>, L<guestfs-internals(1)>, L<guestfs-performance(1)>,
L<guestfs-release-notes(1)>, L<guestfs-security(1)>, L<guestfs-testing(1)>,
L<libguestfs-test-tool(1)>, L<libguestfs-make-fixed-appliance(1)>.

Related manual pages: L<supermin(1)>, L<qemu(1)>, L<hivex(3)>, L<stap(1)>,
L<sd-journal(3)>.

Website: L<http://libguestfs.org/>

同じ目的を持つツール: L<fdisk(8)>, L<parted(8)>, L<kpartx(8)>, L<lvm(8)>,
L<disktype(1)>.

=head1 著者

Richard W.M. Jones (C<rjones at redhat dot com>)

=head1 COPYRIGHT

Copyright (C) 2009-2019 Red Hat Inc.