Merging upstream version 0.9.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 98 insertions, 38 deletions

diff --git a/doc/tarlz.texi b/doc/tarlz.texi
index 4c6d16a..d9bdc14 100644
--- a/doc/tarlz.texi
+++ b/doc/tarlz.texi
@@ -6,8 +6,8 @@
 @finalout
 @c %**end of header
 
-@set UPDATED 16 December 2018
-@set VERSION 0.8
+@set UPDATED 22 January 2019
+@set VERSION 0.9
 
 @dircategory Data Compression
 @direntry
@@ -39,13 +39,14 @@ This manual is for Tarlz (version @value{VERSION}, @value{UPDATED}).
 * Invoking tarlz::            Command line interface
 * File format::               Detailed format of the compressed archive
 * Amendments to pax format::  The reasons for the differences with pax
+* Multi-threaded tar::        Limitations of parallel tar decoding
 * 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.
+Copyright @copyright{} 2013-2019 Antonio Diaz Diaz.
 
 This manual is free documentation: you have unlimited permission
 to copy, distribute and modify it.
@@ -55,18 +56,20 @@ to copy, distribute and modify it.
 @chapter Introduction
 @cindex introduction
 
-@uref{http://www.nongnu.org/lzip/tarlz.html,,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
-@uref{http://www.nongnu.org/lzip/lzip.html,,lzip} on a per file basis. Each
-tar member is compressed in its own lzip member, as well as the end-of-file
-blocks. This method 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 append files to the end of such compressed
-archives.
-
-Tarlz can create tar archives with four levels of compression
-granularity; per file, per directory, appendable solid, and solid.
+@uref{http://www.nongnu.org/lzip/tarlz.html,,Tarlz} is a combined
+implementation of the tar archiver and the
+@uref{http://www.nongnu.org/lzip/lzip.html,,lzip} compressor. By default
+tarlz creates, lists and extracts archives in a simplified posix pax format
+compressed with lzip on a per file basis. Each tar member is compressed in
+its own lzip member, as well as the end-of-file blocks. This method adds an
+indexed lzip layer on top of the tar archive, making it possible to decode
+the archive safely in parallel. The resulting multimember tar.lz archive is
+fully backward compatible with standard tar tools like GNU tar, which treat
+it like any other tar.lz archive. Tarlz can append files to the end of such
+compressed archives.
+
+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
@@ -76,7 +79,7 @@ following advantages:
 @itemize @bullet
 @item
 The resulting multimember tar.lz archive can be decompressed in
-parallel with plzip, multiplying the decompression speed.
+parallel, multiplying the decompression speed.
 
 @item
 New members can be appended to the archive (by removing the EOF
@@ -102,9 +105,6 @@ standard tar tools. @xref{crc32}.
 Tarlz does not understand other tar formats like @samp{gnu}, @samp{oldgnu},
 @samp{star} or @samp{v7}.
 
-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
@@ -174,6 +174,20 @@ previous @code{-C} option.
 Use archive file @var{archive}. @samp{-} used as an @var{archive}
 argument reads from standard input or writes to standard output.
 
+@item -n @var{n}
+@itemx --threads=@var{n}
+Set the number of decompression threads, overriding the system's default.
+Valid values range from 0 to "as many as your system can support". A value
+of 0 disables threads entirely. If this option is not used, tarlz tries to
+detect the number of processors in the system and use it as default value.
+@w{@samp{tarlz --help}} shows the system's default value. This option
+currently only has effect when listing the contents of a multimember
+compressed archive. @xref{Multi-threaded tar}.
+
+Note that the number of usable threads is limited during decompression to
+the number of lzip members in the tar.lz archive, which you can find by
+running @w{@code{lzip -lv archive.tar.lz}}.
+
 @item -q
 @itemx --quiet
 Quiet operation. Suppress all messages.
@@ -335,6 +349,11 @@ associated fields in this header block for this file.
 Zero or more blocks that contain the contents of the file.
 @end itemize
 
+Each tar member must be contiguously stored in a lzip member for the
+parallel decoding operations like @code{--list} to work. If any tar member
+is split over two or more lzip members, the archive must be decoded
+sequentially. @xref{Multi-threaded tar}.
+
 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
@@ -481,20 +500,12 @@ 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
+@multitable {Bit Name} {Value} {Bit Name} {Value} {Bit Name} {Value}
+@headitem Bit Name @tab Value @tab Bit Name @tab Value @tab Bit Name @tab Value
+@item S_ISUID @tab 04000 @tab S_ISGID @tab 02000 @tab S_ISVTX @tab 01000
+@item S_IRUSR @tab 00400 @tab S_IWUSR @tab 00200 @tab S_IXUSR @tab 00100
+@item S_IRGRP @tab 00040 @tab S_IWGRP @tab 00020 @tab S_IXGRP @tab 00010
+@item S_IROTH @tab 00004 @tab S_IWOTH @tab 00002 @tab S_IXOTH @tab 00001
 @end multitable
 
 The uid and gid fields are the user and group ID of the owner and group
@@ -551,10 +562,13 @@ 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.
+version field contains the characters "00" (0x30,0x30). The fields uname,
+and gname are null-terminated character strings except when all characters
+in the array contain non-null characters including the last character. Each
+numeric field contains a leading space- or zero-filled, optionally
+null-terminated octal number using digits from the ISO/IEC 646:1991 (ASCII)
+standard. Tarlz is able to decode numeric fields 1 byte larger than standard
+ustar by not requiring a terminating null character.
 
 
 @node Amendments to pax format
@@ -574,7 +588,7 @@ concrete reasons to implement them.
 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 filename may cause the extraction of the file in the wrong place
-without warning. Corruption in a long file size may cause the truncation of
+without warning. Corruption in a large file 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.
@@ -636,6 +650,52 @@ double UTF-8 conversions. If the need arises this behavior will be adjusted
 with a command line option in the future.
 
 
+@node Multi-threaded tar
+@chapter Limitations of parallel tar decoding
+
+Safely decoding an arbitrary tar archive in parallel is impossible. For
+example, if a tar archive containing another tar archive is decoded starting
+from some position other than the beginning, there is no way to know if the
+first header found there belongs to the outer tar archive or to the inner
+tar archive. Tar is a format inherently serial; it was designed for tapes.
+
+In the case of compressed tar archives, the start of each compressed block
+determines one point through which the tar archive can be decoded in
+parallel. Therefore, in tar.lz archives the decoding operations can't be
+parallelized if the tar members are not aligned with the lzip members. Tar
+archives compressed with plzip can't be decoded in parallel because tar and
+plzip do not have a way to align both sets of members. Certainly one can
+decompress one such archive with a multi-threaded tool like plzip, but the
+increase in speed is not as large as it could be because plzip must
+serialize the decompressed data and pass them to tar, which decodes them
+sequentially, one tar member at a time.
+
+On the other hand, if the tar.lz archive is created with a tool like tarlz,
+which can guarantee the alignment between tar members and lzip members
+because it controls both archiving and compression, then the lzip format
+becomes an indexed layer on top of the tar archive which makes possible
+decoding it safely in parallel.
+
+Tarlz is able to automatically decode aligned and unaligned multimember
+tar.lz archives, keeping backwards compatibility. If tarlz finds a member
+misalignment during multi-threaded decoding, it switches to single-threaded
+mode and continues decoding the archive. Currently only the @code{--list}
+option is able to do multi-threaded decoding.
+
+If the files in the archive are large, multi-threaded @code{--list} on a
+regular tar.lz archive can be hundreds of times faster than sequential
+@code{--list} because, in addition to using several processors, it only
+needs to decompress part of each lzip member. See the following example
+listing the Silesia corpus on a dual core machine:
+
+@example
+tarlz -9 -cf silesia.tar.lz silesia
+time lzip -cd silesia.tar.lz | tar -tf -            (5.032s)
+time plzip -cd silesia.tar.lz | tar -tf -           (3.256s)
+time tarlz -tf silesia.tar.lz                       (0.020s)
+@end example
+
+
 @node Examples
 @chapter A small tutorial with examples
 @cindex examples