\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename tarlz.info
@documentencoding ISO-8859-15
@settitle Tarlz Manual
@finalout
@c %**end of header

@set UPDATED 29 September 2018
@set VERSION 0.5

@dircategory Data Compression
@direntry
* Tarlz: (tarlz).               Archiver with multimember lzip compression
@end direntry


@ifnothtml
@titlepage
@title Tarlz
@subtitle Archiver with multimember lzip compression
@subtitle for Tarlz version @value{VERSION}, @value{UPDATED}
@author by Antonio Diaz Diaz

@page
@vskip 0pt plus 1filll
@end titlepage

@contents
@end ifnothtml

@node Top
@top

This manual is for Tarlz (version @value{VERSION}, @value{UPDATED}).

@menu
* Introduction::           Purpose and features of tarlz
* Invoking tarlz::         Command line interface
* File format::            Detailed format of the compressed archive
* Examples::               A small tutorial with examples
* Problems::               Reporting bugs
* Concept index::          Index of concepts
@end menu

@sp 1
Copyright @copyright{} 2013-2018 Antonio Diaz Diaz.

This manual is free documentation: you have unlimited permission
to copy, distribute and modify it.


@node Introduction
@chapter Introduction
@cindex introduction

Tarlz is a small and simple implementation of the tar archiver. By
default tarlz creates, lists and extracts archives in a simplified posix
pax format compressed with lzip on a per file basis. Tarlz can append
files to the end of such compressed archives.

Each tar member is compressed in its own lzip member, as well as the
end-of-file blocks. This same method works for any tar format (gnu,
ustar, posix) and is fully backward compatible with standard tar tools
like GNU tar, which treat the resulting multimember tar.lz archive like
any other tar.lz archive.

Tarlz can create tar archives with four levels of compression
granularity; per file, per directory, appendable solid, and solid.

@noindent
Of course, compressing each file (or each directory) individually is
less efficient than compressing the whole tar archive, but it has the
following advantages:

@itemize @bullet
@item
The resulting multimember tar.lz archive can be decompressed in
parallel with plzip, multiplying the decompression speed.

@item
New members can be appended to the archive (by removing the eof
member) just like to an uncompressed tar archive.

@item
It is a safe posix-style backup format. In case of corruption,
tarlz can extract all the undamaged members from the tar.lz
archive, skipping over the damaged members, just like the standard
(uncompressed) tar. Moreover, lziprecover can be used to recover at
least part of the contents of the damaged members.

@item
A multimember tar.lz archive is usually smaller than the
corresponding solidly compressed tar.gz archive, except when
individually compressing files smaller than about 32 KiB.
@end itemize

Note that the posix pax format has a serious flaw. The metadata stored
in pax extended records are not protected by any kind of check sequence.
Corruption in a long name may cause the extraction of the file in the
wrong place without warning. Corruption in a long size may cause the
truncation of the file or the appending of garbage to the file, both
followed by a spurious warning about a corrupt header far from the place
of the undetected corruption.

Metadata like filename and file size must be always protected in an
archive format because of the adverse effects of undetected corruption
in them, potentially much worse that undetected corruption in the data.
Even more so in the case of pax because the amount of metadata it stores
is potentially large, making undetected corruption more probable.

Because of the above, tarlz implements a CRC of the extended records
(@pxref{crc32}) and an option to ignore a missing CRC in archives not
created by tarlz (@pxref{--ignore-crc}).

Tarlz is intended as a showcase project for the maintainers of real tar
programs to evaluate the format and perhaps implement it in their tools.


@node Invoking tarlz
@chapter Invoking tarlz
@cindex invoking
@cindex options
@cindex usage
@cindex version

The format for running tarlz is:

@example
tarlz [@var{options}] [@var{files}]
@end example

@noindent
On archive creation or appending, tarlz removes leading and trailing
slashes from filenames, as well as filename prefixes containing a
@samp{..} component. On extraction, archive members containing a
@samp{..} component are skipped.

tarlz supports the following options:

@table @code
@item -h
@itemx --help
Print an informative help message describing the options and exit.

@item -V
@itemx --version
Print the version number of tarlz on the standard output and exit.
This version number should be included in all bug reports.

@item -c
@itemx --create
Create a new archive from @var{files}.

@item -C @var{dir}
@itemx --directory=@var{dir}
Change to directory @var{dir}. When creating or appending, the position
of each @code{-C} option in the command line is significant; it will
change the current working directory for the following @var{files} until
a new @code{-C} option appears in the command line. When extracting, all
the @code{-C} options are executed in sequence before starting the
extraction. Listing ignores any @code{-C} options specified. @var{dir}
is relative to the then current working directory, perhaps changed by a
previous @code{-C} option.

@item -f @var{archive}
@itemx --file=@var{archive}
Use archive file @var{archive}. @samp{-} used as an @var{archive}
argument reads from standard input or writes to standard output.

@item -q
@itemx --quiet
Quiet operation. Suppress all messages.

@item -r
@itemx --append
Append files to the end of an archive. The archive must be a regular
(seekable) file compressed as a multimember lzip file, and the two
end-of-file blocks plus any zero padding must be contained in the last
lzip member of the archive. First this last member is removed, then the
new members are appended, and then a new end-of-file member is appended
to the archive. Exit with status 0 without modifying the archive if no
@var{files} have been specified. tarlz can't append files to an
uncompressed tar archive.

@item -t
@itemx --list
List the contents of an archive. If @var{files} are given, list only the
given @var{files}.

@item -v
@itemx --verbose
Verbosely list files processed.

@item -x
@itemx --extract
Extract files from an archive. If @var{files} are given, extract only
the given @var{files}. Else extract all the files in the archive.

@item -0 .. -9
Set the compression level. The default compression level is @samp{-6}.

@item --asolid
When creating or appending to a compressed archive, use appendable solid
compression. All the files being added to the archive are compressed
into a single lzip member, but the end-of-file blocks are compressed
into a separate lzip member. This creates a solidly compressed
appendable archive.

@item --dsolid
When creating or appending to a compressed archive, use solid
compression for each directory especified in the command line. The
end-of-file blocks are compressed into a separate lzip member. This
creates a compressed appendable archive with a separate lzip member for
each top-level directory.

@item --solid
When creating or appending to a compressed archive, use solid
compression. The files being added to the archive, along with the
end-of-file blocks, are compressed into a single lzip member. The
resulting archive is not appendable. No more files can be later appended
to the archive without decompressing it first.

@item --group=@var{group}
When creating or appending, use @var{group} for files added to the
archive. If @var{group} is not a valid group name, it is decoded as a
decimal numeric group ID.

@item --owner=@var{owner}
When creating or appending, use @var{owner} for files added to the
archive. If @var{owner} is not a valid user name, it is decoded as a
decimal numeric user ID.

@anchor{--ignore-crc}
@item --ignore-crc
Ignore a missing CRC in the extended records. Useful when reading an
archive not created by tarlz.

@ignore
@item --permissive
Allow some violations of the archive format, like consecutive extended
headers preceding a ustar header, or several records with the same
keyword appearing in the same block of extended records.
@end ignore

@item --uncompressed
With @code{--create}, don't compress the created tar archive. Create an
uncompressed tar archive instead.

@end table

Exit status: 0 for a normal exit, 1 for environmental problems (file not
found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
invalid input file, 3 for an internal consistency error (eg, bug) which
caused tarlz to panic.


@node File format
@chapter File format
@cindex file format

In the diagram below, a box like this:
@verbatim
+---+
|   | <-- the vertical bars might be missing
+---+
@end verbatim

represents one byte; a box like this:
@verbatim
+==============+
|              |
+==============+
@end verbatim

represents a variable number of bytes or a fixed but large number of
bytes (for example 512).

@sp 1
A tar.lz file consists of a series of lzip members (compressed data sets).
The members simply appear one after another in the file, with no
additional information before, between, or after them.

Each lzip member contains one or more tar members in a simplified posix
pax interchange format; the only pax typeflag value supported by tarlz
(in addition to the typeflag values defined by the ustar format) is
@samp{x}. The pax format is an extension on top of the ustar format that
removes the size limitations of the ustar format.

Each tar member contains one file archived, and is represented by the
following sequence:

@itemize @bullet
@item
An optional extended header block with extended header records. This
header block is of the form described in pax header block, with a
typeflag value of @samp{x}. The extended header records are included as
the data for this header block.

@item
A header block in ustar format that describes the file. Any fields
defined in the preceding optional extended header records override the
associated fields in this header block for this file.

@item
Zero or more blocks that contain the contents of the file.
@end itemize

At the end of the archive file there are two 512-byte blocks filled with
binary zeros, interpreted as an end-of-archive indicator. These EOF
blocks are either compressed in a separate lzip member or compressed
along with the tar members contained in the last lzip member.

The diagram below shows the correspondence between each tar member
(formed by one or two headers plus optional data) in the tar archive and
each
@uref{http://www.nongnu.org/lzip/manual/lzip_manual.html#File-format,,lzip member}
in the resulting multimember tar.lz archive:
@ifnothtml
@xref{File format,,,lzip}.
@end ifnothtml

@verbatim
tar
+========+======+=================+===============+========+======+========+
| header | data | extended header | extended data | header | data |   eof  |
+========+======+=================+===============+========+======+========+

tar.lz
+===============+=================================================+========+
|     member    |                      member                     | member |
+===============+=================================================+========+
@end verbatim

@ignore
When @code{--permissive} is used, the following violations of the
archive format are allowed:@*
If several extended headers precede an ustar header, only the last
extended header takes effect. The other extended headers are ignored.
Similarly, if several records with the same keyword appear in the same
block of extended records, only the last record for the repeated keyword
takes effect. The other records for the repeated keyword are ignored.
@end ignore

@sp 1
@section Pax header block

The pax header block is identical to the ustar header block described
below except that the typeflag has the value @samp{x} (extended). The
size field is the size of the extended header data in bytes. The other
fields in the pax header block are set on archive creation to values
that provide reasonable file access if the archive is read by an ustar
tool, and are ignored by tarlz on archive extraction. A difference with
posix pax is that tarlz stores (for now) the name field as-is, limited
to a length of 100 bytes.

The pax extended header data consists of one or more records, each of
them constructed as follows:@*
@code{"%d %s=%s\n", <length>, <keyword>, <value>}

The <length>, <blank>, <keyword>, <equals-sign>, and <newline> in the
record must be limited to the portable character set. The <length> field
contains the decimal length of the record in bytes, including the
trailing <newline>. The <value> field is stored as-is, without
conversion to UTF-8 nor any other transformation.

These are the <keyword> fields currently supported by tarlz:

@table @code
@item linkpath
The pathname of a link being created to another file, of any type,
previously archived. This record overrides the linkname field in the
following ustar header block. The following ustar header block
determines the type of link created. If typeflag of the following header
block is 1, it will be a hard link. If typeflag is 2, it will be a
symbolic link and the linkpath value will be used as the contents of the
symbolic link.

@item path
The pathname of the following file. This record overrides the name and
prefix fields in the following ustar header block.

@item size
The size of the file in bytes, expressed as a decimal number using
digits from the ISO/IEC 646:1991 (ASCII) standard. This record overrides
the size field in the following ustar header block. The size record is
used only for files with a size value greater than 8_589_934_591
@w{(octal 77777777777)}. This is 2^33 bytes or larger.

@anchor{crc32}
@item GNU.crc32
CRC32-C (Castagnoli) of the extended header data excluding the 8 bytes
representing the CRC <value> itself. The <value> is represented as 8
hexadecimal digits in big endian order,
@w{@samp{22 GNU.crc32=00000000\n}}. The keyword of the CRC record needs
to be protected to guarante that corruption is always detected (except
in case of CRC collision). A CRC was chosen because a checksum is too
weak for a potentially large list of variable sized records. A checksum
can't detect simple errors like the swapping of two bytes.
@end table

@sp 1
@section Ustar header block

The ustar header block has a length of 512 bytes and is structured as
shown in the following table. All lengths and offsets are in decimal.

@multitable {Field Name} {Offset} {Length (in bytes)}
@item Field Name @tab Offset @tab Length (in bytes)
@item name     @tab   0 @tab 100
@item mode     @tab 100 @tab   8
@item uid      @tab 108 @tab   8
@item gid      @tab 116 @tab   8
@item size     @tab 124 @tab  12
@item mtime    @tab 136 @tab  12
@item chksum   @tab 148 @tab   8
@item typeflag @tab 156 @tab   1
@item linkname @tab 157 @tab 100
@item magic    @tab 257 @tab   6
@item version  @tab 263 @tab   2
@item uname    @tab 265 @tab  32
@item gname    @tab 297 @tab  32
@item devmajor @tab 329 @tab   8
@item devminor @tab 337 @tab   8
@item prefix   @tab 345 @tab 155
@end multitable

All characters in the header block are coded using the ISO/IEC 646:1991
(ASCII) standard, except in fields storing names for files, users, and
groups. For maximum portability between implementations, names should
only contain characters from the portable filename character set. But if
an implementation supports the use of characters outside of @samp{/} and
the portable filename character set in names for files, users, and
groups, tarlz will use the byte values in these names unmodified.

The fields name, linkname, and prefix are null-terminated character
strings except when all characters in the array contain non-null
characters including the last character.

The name and the prefix fields produce the pathname of the file. A new
pathname is formed, if prefix is not an empty string (its first
character is not null), by concatenating prefix (up to the first null
character), a <slash> character, and name; otherwise, name is used
alone. In either case, name is terminated at the first null character.
If prefix begins with a null character, it is ignored. In this manner,
pathnames of at most 256 characters can be supported. If a pathname does
not fit in the space provided, an extended record is used to store the
pathname.

The linkname field does not use the prefix to produce a pathname. If the
linkname does not fit in the 100 characters provided, an extended record
is used to store the linkname.

The mode field provides 12 access permission bits. The following table
shows the symbolic name of each bit and its octal value:

@multitable {Bit Name} {Bit value}
@item Bit Name @tab Bit value
@item S_ISUID @tab 04000
@item S_ISGID @tab 02000
@item S_ISVTX @tab 01000
@item S_IRUSR @tab 00400
@item S_IWUSR @tab 00200
@item S_IXUSR @tab 00100
@item S_IRGRP @tab 00040
@item S_IWGRP @tab 00020
@item S_IXGRP @tab 00010
@item S_IROTH @tab 00004
@item S_IWOTH @tab 00002
@item S_IXOTH @tab 00001
@end multitable

The uid and gid fields are the user and group ID of the owner and group
of the file, respectively.

The size field contains the octal representation of the size of the file
in bytes. If the typeflag field specifies a file of type '0' (regular
file) or '7' (high performance regular file), the number of logical
records following the header is @w{(size / 512)} rounded to the next
integer. For all other values of typeflag, tarlz either sets the size
field to 0 or ignores it, and does not store or expect any logical
records following the header. If the file size is larger than
8_589_934_591 bytes @w{(octal 77777777777)}, an extended record is used
to store the file size.

The mtime field contains the octal representation of the modification
time of the file at the time it was archived, obtained from the stat()
function.

The chksum field contains the octal representation of the value of the
simple sum of all bytes in the header logical record. Each byte in the
header is treated as an unsigned value. When calculating the checksum,
the chksum field is treated as if it were all <space> characters.

The typeflag field contains a single character specifying the type of
file archived:

@table @code
@item '0'
Regular file.

@item '1'
Hard link to another file, of any type, previously archived.

@item '2'
Symbolic link.

@item '3', '4'
Character special file and block special file respectively. In this case
the devmajor and devminor fields contain information defining the
device in unspecified format.

@item '5'
Directory.

@item '6'
FIFO special file.

@item '7'
Reserved to represent a file to which an implementation has associated
some high-performance attribute. Tarlz treats this type of file as a
regular file (type 0).

@end table

The magic field contains the ASCII null-terminated string "ustar". The
version field contains the characters "00" (0x30,0x30). The fields
uname, and gname are null-terminated character strings. Each numeric
field contains a leading zero-filled, null-terminated octal number using
digits from the ISO/IEC 646:1991 (ASCII) standard.


@node Examples
@chapter A small tutorial with examples
@cindex examples

@noindent
Example 1: Create a multimember compressed archive @samp{archive.tar.lz}
containing files @samp{a}, @samp{b} and @samp{c}.

@example
tarlz -cf archive.tar.lz a b c
@end example

@sp 1
@noindent
Example 2: Append files @samp{d} and @samp{e} to the multimember
compressed archive @samp{archive.tar.lz}.

@example
tarlz -rf archive.tar.lz d e
@end example

@sp 1
@noindent
Example 3: Create a solidly compressed appendable archive
@samp{archive.tar.lz} containing files @samp{a}, @samp{b} and @samp{c}.
Then append files @samp{d} and @samp{e} to the archive.

@example
tarlz --asolid -cf archive.tar.lz a b c
tarlz --asolid -rf archive.tar.lz d e
@end example

@sp 1
@noindent
Example 4: Create a compressed appendable archive containing directories
@samp{dir1}, @samp{dir2} and @samp{dir3} with a separate lzip member per
directory. Then append files @samp{a}, @samp{b}, @samp{c}, @samp{d} and
@samp{e} to the archive, all of them contained in a single lzip member.
The resulting archive @samp{archive.tar.lz} contains 5 lzip members
(including the eof member).

@example
tarlz --dsolid -cf archive.tar.lz dir1 dir2 dir3
tarlz --asolid -rf archive.tar.lz a b c d e
@end example

@sp 1
@noindent
Example 5: Create a solidly compressed archive @samp{archive.tar.lz}
containing files @samp{a}, @samp{b} and @samp{c}. Note that no more
files can be later appended to the archive without decompressing it
first.

@example
tarlz --solid -cf archive.tar.lz a b c
@end example

@sp 1
@noindent
Example 6: Extract all files from archive @samp{archive.tar.lz}.

@example
tarlz -xf archive.tar.lz
@end example

@sp 1
@noindent
Example 7: Extract files @samp{a} and @samp{c} from archive
@samp{archive.tar.lz}.

@example
tarlz -xf archive.tar.lz a c
@end example

@sp 1
@noindent
Example 8: Copy the contents of directory @samp{sourcedir} to the
directory @samp{targetdir}.

@example
tarlz -C sourcedir -c . | tarlz -C targetdir -x
@end example


@node Problems
@chapter Reporting bugs
@cindex bugs
@cindex getting help

There are probably bugs in tarlz. There are certainly errors and
omissions in this manual. If you report them, they will get fixed. If
you don't, no one will ever know about them and they will remain unfixed
for all eternity, if not longer.

If you find a bug in tarlz, please send electronic mail to
@email{lzip-bug@@nongnu.org}. Include the version number, which you can
find by running @w{@code{tarlz --version}}.


@node Concept index
@unnumbered Concept index

@printindex cp

@bye
