Merging upstream version 0.9.

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

1 files changed, 109 insertions, 44 deletions

diff --git a/doc/tarlz.info b/doc/tarlz.info
index d6d17d0..7f90766 100644
--- a/doc/tarlz.info
+++ b/doc/tarlz.info
@@ -11,7 +11,7 @@ File: tarlz.info,  Node: Top,  Next: Introduction,  Up: (dir)
 Tarlz Manual
 ************
 
-This manual is for Tarlz (version 0.8, 16 December 2018).
+This manual is for Tarlz (version 0.9, 22 January 2019).
 
 * Menu:
 
@@ -19,12 +19,13 @@ This manual is for Tarlz (version 0.8, 16 December 2018).
 * 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
 
 
-   Copyright (C) 2013-2018 Antonio Diaz Diaz.
+   Copyright (C) 2013-2019 Antonio Diaz Diaz.
 
    This manual is free documentation: you have unlimited permission to
 copy, distribute and modify it.
@@ -35,12 +36,14 @@ File: tarlz.info,  Node: Introduction,  Next: Invoking tarlz,  Prev: Top,  Up: T
 1 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. 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
+Tarlz is a combined implementation of the tar archiver and the 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.
 
@@ -52,7 +55,7 @@ less efficient than compressing the whole tar archive, but it has the
 following advantages:
 
    * The resulting multimember tar.lz archive can be decompressed in
-     parallel with plzip, multiplying the decompression speed.
+     parallel, multiplying the decompression speed.
 
    * New members can be appended to the archive (by removing the EOF
      member) just like to an uncompressed tar archive.
@@ -74,10 +77,6 @@ with standard tar tools. *Note crc32::.
    Tarlz does not understand other tar formats like 'gnu', 'oldgnu',
 'star' or '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.
-
 
 File: tarlz.info,  Node: Invoking tarlz,  Next: File format,  Prev: Introduction,  Up: Top
 
@@ -141,6 +140,21 @@ archive 'foo'.
      Use archive file ARCHIVE. '-' used as an ARCHIVE argument reads
      from standard input or writes to standard output.
 
+'-n N'
+'--threads=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.  'tarlz --help' shows the
+     system's default value. This option currently only has effect when
+     listing the contents of a multimember compressed archive. *Note
+     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 'lzip -lv archive.tar.lz'.
+
 '-q'
 '--quiet'
      Quiet operation. Suppress all messages.
@@ -288,6 +302,11 @@ following sequence:
 
    * Zero or more blocks that contain the contents of the file.
 
+   Each tar member must be contiguously stored in a lzip member for the
+parallel decoding operations like '--list' to work. If any tar member
+is split over two or more lzip members, the archive must be decoded
+sequentially. *Note 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
@@ -417,19 +436,12 @@ 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:
 
-Bit Name   Bit value
-S_ISUID    04000
-S_ISGID    02000
-S_ISVTX    01000
-S_IRUSR    00400
-S_IWUSR    00200
-S_IXUSR    00100
-S_IRGRP    00040
-S_IWGRP    00020
-S_IXGRP    00010
-S_IROTH    00004
-S_IWOTH    00002
-S_IXOTH    00001
+Bit Name   Value   Bit Name   Value   Bit Name   Value
+---------------------------------------------------
+S_ISUID    04000   S_ISGID    02000   S_ISVTX    01000
+S_IRUSR    00400   S_IWUSR    00200   S_IXUSR    00100
+S_IRGRP    00040   S_IWGRP    00020   S_IXGRP    00010
+S_IROTH    00004   S_IWOTH    00002   S_IXOTH    00001
 
    The uid and gid fields are the user and group ID of the owner and
 group of the file, respectively.
@@ -485,12 +497,16 @@ file archived:
 
    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.
+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.
 
 
-File: tarlz.info,  Node: Amendments to pax format,  Next: Examples,  Prev: File format,  Up: Top
+File: tarlz.info,  Node: Amendments to pax format,  Next: Multi-threaded tar,  Prev: File format,  Up: Top
 
 4 The reasons for the differences with pax
 ******************************************
@@ -508,7 +524,7 @@ and the 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
+the wrong place 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.
@@ -573,9 +589,57 @@ prevents accidental double UTF-8 conversions. If the need arises this
 behavior will be adjusted with a command line option in the future.
 
 
-File: tarlz.info,  Node: Examples,  Next: Problems,  Prev: Amendments to pax format,  Up: Top
+File: tarlz.info,  Node: Multi-threaded tar,  Next: Examples,  Prev: Amendments to pax format,  Up: Top
+
+5 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 '--list' option is able to do multi-threaded decoding.
+
+   If the files in the archive are large, multi-threaded '--list' on a
+regular tar.lz archive can be hundreds of times faster than sequential
+'--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:
+
+     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)
+
+
+File: tarlz.info,  Node: Examples,  Next: Problems,  Prev: Multi-threaded tar,  Up: Top
 
-5 A small tutorial with examples
+6 A small tutorial with examples
 ********************************
 
 Example 1: Create a multimember compressed archive 'archive.tar.lz'
@@ -633,7 +697,7 @@ Example 8: Copy the contents of directory 'sourcedir' to the directory
 
 File: tarlz.info,  Node: Problems,  Next: Concept index,  Prev: Examples,  Up: Top
 
-6 Reporting bugs
+7 Reporting bugs
 ****************
 
 There are probably bugs in tarlz. There are certainly errors and
@@ -670,16 +734,17 @@ Concept index
 
 Tag Table:
 Node: Top223
-Node: Introduction946
-Node: Invoking tarlz3084
-Node: File format9606
-Ref: key_crc3214138
-Node: Amendments to pax format19215
-Ref: crc3219729
-Ref: flawed-compat20753
-Node: Examples23126
-Node: Problems24802
-Node: Concept index25328
+Node: Introduction1012
+Node: Invoking tarlz3124
+Node: File format10384
+Ref: key_crc3215169
+Node: Amendments to pax format20586
+Ref: crc3221110
+Ref: flawed-compat22135
+Node: Multi-threaded tar24508
+Node: Examples27012
+Node: Problems28682
+Node: Concept index29208
 
 End Tag Table