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.\" Copyright (C) 2007-2012 Nippon Telegraph and Telephone Corporation.
.\" Written by Ryusuke Konishi <konishi.ryusuke@gmail.com>
.\"
.TH DUMPSEG 8 "Apr 2014" "nilfs-utils version 2.2"
.SH NAME
dumpseg \- print segment information of NILFS2
.SH SYNOPSIS
.B dumpseg
[\fB\-hV\fP]
.sp
.B dumpseg
[\fIdevice\fP] \fIsegment-number\fP ...
.SH DESCRIPTION
The
.B dumpseg
program is an analysis tool for on-disk logs of a NILFS2 file system
found in \fIdevice\fP. It displays the configuration of every log
stored in the segments specified by one or more \fIsegment-numbers\fP.
The term segment here means a contiguous lump of disk blocks giving an
allocation unit of NILFS2 disk space. When \fIdevice\fP is omitted,
it tries to find an active NILFS2 file system from \fI/proc/mounts\fP.
.PP
.B dumpseg
is a tool for debugging rather than administration. To list a summary
of segments, \fBlssu\fP(1) is available instead.
.SH OPTIONS
.TP
\fB\-h\fR, \fB\-\-help\fR
Display help message and exit.
.TP
\fB\-V\fR, \fB\-\-version\fR
Display version and exit.
.SH "FIELD DESCRIPTION"
.B dumpseg
shows the configuration of each log with the following fields, where
each field is printed in the style of ``\fIfield-name\fP \fB=\fP
\fIvalue\fP''.
.TP
.B creation time
Creation date and time of the log.
.TP
.B nfinfo
Number of file information summaries.
.TP
.B finfo
File information summary. This information starts with the following fields:
.RS
.TP
.B ino
Inode number of the file.
.TP
.B cno
Number of the checkpoint that the blocks included in the file belong
to. For normal writings, this is equal to the latest checkpoint
number. For the writings involved in garbage collection, this
indicates a past checkpoint number.
.TP
.B nblocks
Number of blocks of the file written in the log. This number is a sum
of the number of data blocks and B-tree node blocks. The contents of
these blocks are written serially in the payload part of the log.
Only modified or newly created blocks are written to each log.
.TP
.B ndatblk
Number of data blocks of the file written in the log.
.RE
.TP
.B ""
Then, for each update block in the file, the following information
will follow these headings.
.RS
.TP
.B vblocknr
Virtual block number. Not printed for data blocks of the Disk Address
Translation file (DAT file).
.TP
.B blkoff
Block offset number. Not printed for B-tree node blocks except for
the DAT file.
.TP
.B level
Level of B-tree node block. Printed only for the DAT file.
.TP
.B blocknr
Block address on the \fIdevice\fP. This is not an actual field in the
summary but is calculated from the disk address of each log.
.RE
.RE
.SH AUTHOR
Koji Sato
.SH AVAILABILITY
.B dumpseg
is part of the nilfs-utils package and is available from
https://nilfs.sourceforge.io.
.SH SEE ALSO
.BR nilfs (8),
.BR lssu (1).
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