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|
=head1 NAME
nbdkit-cc-plugin - write small nbdkit plugins in inline C
(and other languages)
=head1 SYNOPSIS
nbdkit cc /path/to/plugin.c [CC=...] [CFLAGS="..."]
[EXTRA_CFLAGS="..."]
[other plugin parameters ...]
=for paragraph
nbdkit cc - <<'EOF'
... C code ...
EOF
=head1 DESCRIPTION
This plugin allows you to write small L<nbdkit(1)> plugins in C (and
some other languages). When you use this plugin it compiles your
source code to a temporary plugin and then jumps into your compiled
plugin. It is somewhat similar to L<nbdkit-sh-plugin(3)>, except for
C source code. This can also be used to write plugins which are "C
scripts".
B<Note> this is not the way you normally write nbdkit plugins in C.
To understand how to write plugins in C normally, read
L<nbdkit-plugin(3)>.
=head2 Simple plugin example
Simple plugins from the nbdkit source tree can be compiled and run
directly using commands such as:
$ nbdkit cc plugins/example1/example1.c EXTRA_CFLAGS="-I. -Iinclude"
You can also read the source from stdin using C<->:
$ nbdkit cc - EXTRA_CFLAGS="-I. -Iinclude" \
< plugins/example1/example1.c
To replace the compiler flags:
$ nbdkit cc plugins/example1/example1.c \
CFLAGS="-O3 -mavx2 -fPIC -shared"
=head2 Compiler name and flags
The plugin parameters C<CC>, C<CFLAGS> and C<EXTRA_CFLAGS> (written in
uppercase) can be used to control which C compiler and C compiler
flags are used. If not set, the default compiler and flags from when
nbdkit was itself compiled from source are used. To see what those
were you can do:
$ nbdkit cc --dump-plugin
...
CC=gcc
CFLAGS=-g -O2 -fPIC -shared
The C<CFLAGS> parameter overrides the built-in flags completely. The
C<EXTRA_CFLAGS> parameter adds extra flags to the built-in flags.
=head2 Plugin API version
Plugins compiled this way must use the same API version as the cc
plugin itself uses. Currently this is C<NBDKIT_API_VERSION=2>.
=head2 C plugin as a self-contained script
You can create a C plugin which is a self-contained script by adding
the following lines at the top and ensuring the C source is executable
(S<C<chmod +x plugin.c>>):
#if 0
exec nbdkit cc "$0" "$@"
#endif
The script can be run as a command with additional nbdkit flags and
plugin parameters, eg:
./plugin.c -f -v
./plugin.c -p 10000 --filter=cow
./plugin.c param=1
=head2 Using this plugin with C++
nbdkit cc CC=g++ source.cpp
C++ plugin scripts can be created similarly to C, but you must add
C<CC=g++> as a parameter to exec nbdkit.
=head2 Using this plugin with OCaml
nbdkit cc CC=ocamlopt \
CFLAGS="-output-obj -runtime-variant _pic __OCAML_STD_INCLUDES__ __OCAML_PLUGIN_LIBRARIES__ NBDKit.cmx -cclib -lnbdkitocaml" \
source.ml
OCaml plugin scripts can be created using this trick:
(*/.)>/dev/null 2>&1
exec nbdkit cc "$0" \
CC=ocamlopt \
CFLAGS="-output-obj -runtime-variant _pic __OCAML_STD_INCLUDES__ __OCAML_PLUGIN_LIBRARIES__ NBDKit.cmx -cclib -lnbdkitocaml" \
"$@"
*)
(* followed by OCaml code for the plugin here *)
As with C plugin scripts, the file must be executable. See also
L<nbdkit-ocaml-plugin(3)>.
=head2 Using this plugin with other programming languages
This plugin can be used with most ahead-of-time compiled programming
languages if they can create shared objects (F<.so> files). The only
requirement is that the compiler (C<CC>) supports an I<-o> option to
write a shared object.
=head1 PARAMETERS
The script name, or C<->, must appear as the first parameter.
=over 4
=item B<CC=>CC
=item B<CFLAGS=">CFLAGSB<">
=item B<EXTRA_CFLAGS=">EXTRA_CFLAGSB<">
Override the compiler and flags. See L</Compiler name and flags>
above.
=back
All other parameters on the command line are passed to the plugin.
=head1 EXAMPLE
$ nbdkit cc - <<'EOF'
#include <stdint.h>
#include <string.h>
#define NBDKIT_API_VERSION 2
#include <nbdkit-plugin.h>
char data[10*1024*1024];
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
static void *
my_open (int readonly)
{
return NBDKIT_HANDLE_NOT_NEEDED;
}
static int64_t
my_get_size (void *handle)
{
return (int64_t) sizeof (data);
}
static int
my_pread (void *handle, void *buf,
uint32_t count, uint64_t offset,
uint32_t flags)
{
memcpy (buf, data+offset, count);
return 0;
}
static int
my_pwrite (void *handle, const void *buf,
uint32_t count, uint64_t offset,
uint32_t flags)
{
memcpy (data+offset, buf, count);
return 0;
}
static struct nbdkit_plugin plugin = {
.name = "myplugin",
.open = my_open,
.get_size = my_get_size,
.pread = my_pread,
.pwrite = my_pwrite,
};
NBDKIT_REGISTER_PLUGIN(plugin)
EOF
=head1 FILES
=over 4
=item F<$plugindir/nbdkit-cc-plugin.so>
The plugin.
Use C<nbdkit --dump-config> to find the location of C<$plugindir>.
=back
=head1 VERSION
C<nbdkit-cc-plugin> first appeared in nbdkit 1.22.
=head1 SEE ALSO
L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-eval-plugin(3)>,
L<nbdkit-ocaml-plugin(3)>,
L<nbdkit-sh-plugin(3)>.
=head1 AUTHORS
Richard W.M. Jones
=head1 COPYRIGHT
Copyright Red Hat
|
