source: trunk/essentials/app-arch/tar/doc/genfile.texi

@c This is part of the paxutils manual.
@c Copyright (C) 2005, 2006 Free Software Foundation, Inc.
@c Written by Sergey Poznyakoff
@c This file is distributed under GFDL 1.1 or any later version
@c published by the Free Software Foundation.

@cindex genfile
    This appendix describes @command{genfile}, an auxiliary program
used in the GNU tar testsuite. If you are not interested in developing
GNU tar, skip this appendix.

    Initially, @command{genfile} was used to generate data files for
the testsuite, hence its name. However, new operation modes were being
implemented as the testsuite grew more sophisticated, and now
@command{genfile} is a multi-purpose instrument.

    There are three basic operation modes:

@table @asis
@item File Generation
    This is the default mode. In this mode, @command{genfile}
generates data files.

@item File Status
    In this mode @command{genfile} displays status of specified files.

@item Synchronous Execution.
    In this mode @command{genfile} executes the given program with
@option{--checkpoint} option and executes a set of actions when
specified checkpoints are reached.
@end table

@menu
* Generate Mode::     File Generation Mode.
* Status Mode::       File Status Mode.
* Exec Mode::         Synchronous Execution mode.
@end menu

@node Generate Mode
@appendixsec Generate Mode

@cindex Generate Mode, @command{genfile}
@cindex @command{genfile}, generate mode
@cindex @command{genfile}, create file
    In this mode @command{genfile} creates a data file for the test
suite. The size of the file is given with the @option{--length}
(@option{-l}) option. By default the file contents is written to the
standard output, this can be changed using @option{--file}
(@option{-f}) command line option. Thus, the following two commands
are equivalent:

@smallexample
@group
genfile --length 100 > outfile
genfile --length 100 --file outfile
@end group
@end smallexample

    If @option{--length} is not given, @command{genfile} will
generate an empty (zero-length) file.

@cindex @command{genfile}, seeking to a given offset
    The command line option @option{--seek=@var{N}} istructs @command{genfile}
to skip the given number of bytes (@var{N}) in the output file before
writing to it.  It is similar to the @option{seek=@var{N}} of the
@command{dd} utility.

@cindex @command{genfile}, reading a list of file names
    You can instruct @command{genfile} to create several files at one
go, by giving it @option{--files-from} (@option{-T}) option followed
by a name of file containing a list of file names. Using dash
(@samp{-}) instead of the file name causes @command{genfile} to read
file list from the standard input. For example:

@smallexample
@group
# Read file names from file @file{file.list}
genfile --files-from file.list
# Read file names from standard input
genfile --files-from -
@end group
@end smallexample

@cindex File lists separated by NUL characters
    The list file is supposed to contain one file name per line. To
use file lists separated by ASCII NUL character, use @option{--null}
(@option{-0}) command line option:

@smallexample
genfile --null --files-from file.list
@end smallexample

@cindex pattern, @command{genfile}
    The default data pattern for filling the generated file consists
of first 256 letters of ASCII code, repeated enough times to fill the
entire file. This behavior can be changed with @option{--pattern}
option. This option takes a mandatory argument, specifying pattern
name to use. Currently two patterns are implemented:

@table @option
@item --pattern=default
    The default pattern as described above.

@item --pattern=zero
    Fills the file with zeroes.
@end table

    If no file name was given, the program exits with the code
@code{0}.  Otherwise, it exits with @code{0} only if it was able to
create a file of the specified length.
    
@cindex Sparse files, creating using @command{genfile}
@cindex @command{genfile}, creating sparse files
    Special option @option{--sparse} (@option{-s}) instructs
@command{genfile} to create a sparse file. Sparse files consist of
@dfn{data fragments}, separated by @dfn{holes} or blocks of zeros. On
many operating systems, actual disk storage is not allocated for
holes, but they are counted in the length of the file. To create a
sparse file, @command{genfile} should know where to put data fragments,
and what data to use to fill them. So, when @option{--sparse} is given
the rest of the command line specifies a so-called @dfn{file map}.

    The file map consists of any number of @dfn{fragment
descriptors}. Each descriptor is composed of two values: a number,
specifying fragment offset from the end of the previous fragment or,
for the very first fragment, from the beginning of the file, and
@dfn{contents string}, i.e., a string of characters, specifying the
pattern to fill the fragment with. File offset can be suffixed with
the following quantifiers:

@table @samp
@item k
@itemx K
The number is expressed in kilobytes.
@item m
@itemx M
The number is expressed in megabytes.
@item g
@itemx G
The number is expressed in gigabytes.
@end table

    For each letter in contents string @command{genfile} will generate
a @dfn{block} of data, filled with this letter and will write it to
the fragment. The size of block is given by @option{--block-size}
option. It defaults to 512. Thus, if the string consists of @var{n}
characters, the resulting file fragment will contain
@code{@var{n}*@var{block-size}} of data. 

    Last fragment descriptor can have only file offset part. In this
case @command{genfile} will create a hole at the end of the file up to
the given offset.

    For example, consider the following invocation:

@smallexample
genfile --sparse --file sparsefile 0 ABCD 1M EFGHI 2000K 
@end smallexample

@noindent
It will create 3101184-bytes long file of the following structure:

@multitable @columnfractions .35 .20 .45
@item Offset  @tab Length       @tab Contents
@item 0       @tab 4*512=2048   @tab Four 512-byte blocks, filled with
letters @samp{A}, @samp{B}, @samp{C} and @samp{D}.
@item 2048    @tab 1046528      @tab Zero bytes 
@item 1050624 @tab 5*512=2560   @tab Five blocks, filled with letters
@samp{E}, @samp{F}, @samp{G}, @samp{H}, @samp{I}.
@item 1053184  @tab 2048000     @tab Zero bytes
@end multitable

    The exit code of @command{genfile --status} command is @code{0}
only if created file is actually sparse.
    
@node Status Mode
@appendixsec Status Mode

    In status mode, @command{genfile} prints file system status for
each file specified in the command line. This mode is toggled by
@option{--stat} (@option{-S}) command line option. An optional argument to this
option specifies output @dfn{format}: a comma-separated list of
@code{struct stat} fields to be displayed. This list can contain
following identifiers @FIXME{should we also support @samp{%} notations
as in stat(1)??}:

@table @asis
@item name
    The file name.
    
@item dev
@itemx st_dev
    Device number in decimal.
    
@item ino
@itemx st_ino
    Inode number.
    
@item mode[.@var{number}]
@itemx st_mode[.@var{number}]
    File mode in octal.  Optional @var{number} specifies octal mask to
be applied to the mode before outputting.  For example, @code{--stat
mode.777} will preserve lower nine bits of it.  Notice, that you can
use any punctuation character in place of @samp{.}.
    
@item nlink
@itemx st_nlink
    Number of hard links.
    
@item uid
@itemx st_uid
    User ID of owner.
    
@item gid
@itemx st_gid
    Group ID of owner.
    
@item size
@itemx st_size
    File size in decimal.
    
@item blksize
@itemx st_blksize
    The size in bytes of each file block.
    
@item blocks
@itemx st_blocks
    Number of blocks allocated.
     
@item atime
@itemx st_atime
    Time of last access.
    
@item mtime
@itemx st_mtime
    Time of last modification

@item ctime
@itemx st_ctime
    Time of last status change

@item sparse
    A boolean value indicating whether the file is @samp{sparse}.     
@end table

    Modification times are displayed in @acronym{UTC} as
@acronym{UNIX} timestamps, unless suffixed with @samp{H} (for
``human-readable''), as in @samp{ctimeH}, in which case usual
@code{tar tv} output format is used.

    The default output format is: @samp{name,dev,ino,mode,
nlink,uid,gid,size,blksize,blocks,atime,mtime,ctime}. 

    For example, the following command will display file names and
corresponding times of last access for each file in the current working
directory:

@smallexample
genfile --stat=name,atime *
@end smallexample

@node Exec Mode
@appendixsec Exec Mode

@cindex Exec Mode, @command{genfile}
    This mode is designed for testing the behavior of @code{paxutils}
commands when some of the files change during archiving. It is an
experimental mode.

    The @samp{Exec Mode} is toggled by @option{--run} command line
option (or its alias @option{-r}). The argument to this option gives
the command line to be executed. The actual command line is
constructed by inserting @option{--checkpoint} option between the
command name and its first argument (if any). Due to this, the
argument to @option{--run} may not use traditional @command{tar}
option syntax, i.e., the following is wrong: 

@smallexample
# Wrong!
genfile --run 'tar cf foo bar'
@end smallexample

@noindent

Use the following syntax instead:

@smallexample
genfile --run 'tar -cf foo bar'
@end smallexample

    The rest of command line after @option{--run} or its equivalent
specifies checkpoint values and actions to be executed upon reaching
them. Checkpoint values are introduced with @option{--checkpoint}
command line option. Argument to this option is the number of
checkpoint in decimal.

    Any number of @dfn{actions} may be specified after a
checkpoint. Available actions are

@table @option
@item --cut @var{file}
@itemx --truncate @var{file}
    Truncate @var{file} to the size specified by previous
@option{--length} option (or 0, if it is not given).
    
@item --append @var{file}
    Append data to @var{file}. The size of data and its pattern are
given by previous @option{--length} and @option{pattern} options.

@item --touch @var{file}
    Update the access and modification times of @var{file}. These
timestamps are changed to the current time, unless @option{--date}
option was given, in which case they are changed to the specified
time. Argument to @option{--date} option is a date specification in
an almost arbitrary format (@pxref{Date input formats}).

@item --exec @var{command}
    Execute given shell command.
    
@end table

    Option @option{--verbose} instructs @command{genfile} to print on
standard output notifications about checkpoints being executed and to
verbosely describe exit status of the command.

    While the command is being executed its standard output remains
connected to descriptor 1. All messages it prints to file descriptor
2, except checkpoint notifications, are forwarded to standard
error.

    @command{Genfile} exits with the exit status of the executed command.