Merging upstream version 1.15~pre1.

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>

1 files changed, 79 insertions, 54 deletions

diff --git a/doc/lziprecover.texinfo b/doc/lziprecover.texinfo
index 142cdae..54834e9 100644
--- a/doc/lziprecover.texinfo
+++ b/doc/lziprecover.texinfo
@@ -6,8 +6,8 @@
 @finalout
 @c %**end of header
 
-@set UPDATED 31 May 2013
-@set VERSION 1.14
+@set UPDATED 17 June 2013
+@set VERSION 1.15-pre1
 
 @dircategory Data Compression
 @direntry
@@ -35,12 +35,14 @@
 This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}).
 
 @menu
-* Introduction::          Purpose and features of lziprecover
-* Invoking Lziprecover::  Command line interface
-* File Format::           Detailed format of the compressed file
-* Examples::              A small tutorial with examples
-* Problems::              Reporting bugs
-* Concept Index::         Index of concepts
+* Introduction::           Purpose and features of lziprecover
+* Invoking Lziprecover::   Command line interface
+* Repairing Files::        Fixing bit-flip and similar errors
+* Merging Files::          Fixing several damaged copies
+* File Format::            Detailed format of the compressed file
+* Examples::               A small tutorial with examples
+* Problems::               Reporting bugs
+* Concept Index::          Index of concepts
 @end menu
 
 @sp 1
@@ -56,14 +58,15 @@ to copy, distribute and modify it.
 
 Lziprecover is a data recovery tool and decompressor for files in the
 lzip compressed data format (.lz) able to repair slightly damaged files,
-recover badly damaged files from two or more copies, extract undamaged
-members from multi-member files, decompress files and test integrity of
-files.
+recover badly damaged files from two or more copies, extract data from
+damaged files, decompress files and test integrity of files.
 
 Lziprecover is able to recover or decompress files produced by any of
 the compressors in the lzip family; lzip, plzip, minilzip/lzlib, clzip
-and pdlzip. This recovery capability contributes to make the lzip format
-one of the best options for long-term data archiving.
+and pdlzip. It makes lzip files resistant to bit-flip, one of the most
+common forms of data corruption, and its recovery capabilities
+contribute to make of the lzip format one of the best options for
+long-term data archiving.
 
 Lziprecover is able to efficiently extract a range of bytes from a
 multi-member file, because it only decompresses the members containing
@@ -80,23 +83,26 @@ damaged files themselves are never modified.
 When decompressing or testing file integrity, lziprecover behaves like
 lzip or lunzip.
 
-If the files are too damaged for lziprecover to repair them, data from
-damaged members can be partially recovered writing it to stdout as shown
-in the following example (the resulting file may contain some garbage
-data at the end):
+If a file is too damaged for lziprecover to repair it, all the
+recoverable data in all members of the file can be extracted with the
+following command (the resulting file may contain errors and some
+garbage data may be produced at the end of each member):
 
 @example
-lziprecover -cd rec01file.lz > rec01file
+lziprecover -D0 -i -o file -q file.lz
 @end example
 
 If the cause of file corruption is damaged media, the combination
 @w{GNU ddrescue + lziprecover} is the best option for recovering data
 from multiple damaged copies. @xref{ddrescue-example}, for an example.
 
+Lziprecover is not a replacement for regular backups, but a last line of
+defense for the case where the backups are also damaged.
+
 
 @node Invoking Lziprecover
 @chapter Invoking Lziprecover
-@cindex invoking lziprecover
+@cindex invoking
 
 The format for running lziprecover is:
 
@@ -164,18 +170,10 @@ information about the members in the file.
 @item -m
 @itemx --merge
 Try to produce a correct file merging the good parts of two or more
-damaged copies. The copies must be single-member files. The merge will
-fail if the copies have too many damaged areas or if the same byte is
-damaged in all copies. If successful, a repaired copy is written to the
-file @samp{@var{file}_fixed.lz}. The exit status is 0 if the file could
-be repaired, 2 otherwise.
-
-To give you an idea of its possibilities, when merging two copies each
-of them with one damaged area affecting 1 percent of the copy, the
-probability of obtaining a correct file is about 98 percent. With three
-such copies the probability rises to 99.97 percent. For large files with
-small errors, the probability approaches 100 percent even with only two
-copies.
+damaged copies. If successful, a repaired copy is written to the file
+@samp{@var{file}_fixed.lz}. The exit status is 0 if a correct file could
+be produced, 2 otherwise. See the chapter Merging Files (@pxref{Merging
+Files}) for a complete description of the merge mode.
 
 @item -o @var{file}
 @itemx --output=@var{file}
@@ -192,10 +190,12 @@ Quiet operation. Suppress all messages.
 
 @item -R
 @itemx --repair
-Try to repair a small error, affecting only one byte, in a single-member
-@var{file}. If successful, a repaired copy is written to the file
+Try to repair a file with small errors (up to one byte error per member).
+If successful, a repaired copy is written to the file
 @samp{@var{file}_fixed.lz}. @samp{@var{file}} is not modified at all.
 The exit status is 0 if the file could be repaired, 2 otherwise.
+See the chapter Repairing Files (@pxref{Repairing Files}) for a complete
+description of the repair mode.
 
 @item -s
 @itemx --split
@@ -252,6 +252,47 @@ invalid input file, 3 for an internal consistency error (eg, bug) which
 caused lziprecover to panic.
 
 
+@node Repairing Files
+@chapter Repairing Files
+@cindex repairing files
+
+Lziprecover is able to repair files with small errors (up to one byte
+error per member). The error may be located anywhere in the file except
+in the header (first 6 bytes of each member) or in the @samp{Member
+size} field of the trailer (last 8 bytes of each member). This makes
+lzip files resistant to bit-flip, one of the most common forms of data
+corruption.
+
+Bit-flip happens when one bit in the file is changed from 0 to 1 or vice
+versa. It may be caused by bad RAM or even by natural radiation. I have
+seen a case of bit-flip in a file stored in an USB flash drive.
+
+
+@node Merging Files
+@chapter Merging Files
+@cindex merging files
+
+If you have several copies of a file but all of them are too damaged to
+repair them (@pxref{Repairing Files}), lziprecover can try to produce a
+correct file merging the good parts of the damaged copies.
+
+The merge may succeed even if some copies of the file have all the
+headers and trailers damaged, as long as there is at least one copy of
+every header and trailer intact, even if they are in different copies of
+the file.
+
+The merge will fail if the damaged areas overlap (at least one byte is
+damaged in all copies), or are adjacent and the boundary can't be
+determined, or if the copies have too many damaged areas.
+
+To give you an idea of its possibilities, when merging two copies each
+of them with one damaged area affecting 1 percent of the copy, the
+probability of obtaining a correct file is about 98 percent. With three
+such copies the probability rises to 99.97 percent. For large files with
+small errors, the probability approaches 100 percent even with only two
+copies.
+
+
 @node File Format
 @chapter File Format
 @cindex file format
@@ -368,9 +409,8 @@ lziprecover -D 10000-15000 file.lz
 
 @sp 1
 @noindent
-Example 5: Repair a one-byte corruption in the single-member file
-@samp{file.lz}. (Indented lines are abridged error messages from
-lziprecover).
+Example 5: Repair small errors in the file @samp{file.lz}. (Indented
+lines are abridged diagnostic messages from lziprecover).
 
 @example
 lziprecover -v -R file.lz
@@ -422,27 +462,12 @@ Example 8: Recover the first volume of those created with the command
 @w{@code{lzip -b 32MiB -S 650MB big_db}} from two copies,
 @samp{big_db1_00001.lz} and @samp{big_db2_00001.lz}, with member 07
 damaged in the first copy, member 18 damaged in the second copy, and
-member 12 damaged in both copies. Two correct copies are produced and
-compared.
+member 12 damaged in both copies. The correct file produced is saved in
+@samp{big_db_00001.lz}.
 
 @example
-lziprecover -s big_db1_00001.lz
-lziprecover -s big_db2_00001.lz
-lziprecover -t rec*big_db1_00001.lz
-  rec07big_db1_00001.lz: crc mismatch
-  rec12big_db1_00001.lz: crc mismatch
-lziprecover -t rec*big_db2_00001.lz
-  rec12big_db2_00001.lz: crc mismatch
-  rec18big_db2_00001.lz: crc mismatch
-lziprecover -m -v rec12big_db1_00001.lz rec12big_db2_00001.lz
+lziprecover -m -v -o big_db_00001.lz big_db1_00001.lz big_db2_00001.lz
   Input files merged successfully
-cp rec07big_db2_00001.lz rec07big_db1_00001.lz
-cp rec12big_db1_00001_fixed.lz rec12big_db1_00001.lz
-cp rec12big_db1_00001_fixed.lz rec12big_db2_00001.lz
-cp rec18big_db1_00001.lz rec18big_db2_00001.lz
-cat rec*big_db1_00001.lz > big_db3_00001.lz
-cat rec*big_db2_00001.lz > big_db4_00001.lz
-zcmp big_db3_00001.lz big_db4_00001.lz
 @end example