X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Fsparse.texi;h=1194357e289208bb6c93abbf47d5de5929dffb89;hb=55abc110f57e77109f687bd62347fc2ce5ec0c5b;hp=7b9145d8ab78ce020c79c3d156c71643f2d1d889;hpb=4d753fced1ed3e2b6edf322c8ae7c3e8b48c948d;p=chaz%2Ftar diff --git a/doc/sparse.texi b/doc/sparse.texi index 7b9145d..1194357 100644 --- a/doc/sparse.texi +++ b/doc/sparse.texi @@ -3,6 +3,8 @@ @c This file is distributed under GFDL 1.1 or any later version @c published by the Free Software Foundation. +@cindex sparse formats +@cindex sparse versions The notion of sparse file, and the ways of handling it from the point of view of @GNUTAR{} user have been described in detail in @ref{sparse}. This chapter describes the internal format @GNUTAR{} @@ -33,6 +35,8 @@ The following subsections describe each format in detail. @node Old GNU Format @appendixsubsec Old GNU Format +@cindex sparse formats, Old GNU +@cindex Old GNU sparse format The format introduced some time around 1990 (v. 1.09). It was designed on top of standard @code{ustar} headers in such an unfortunate way that some of its fields overwrote fields required by @@ -83,24 +87,28 @@ A header with @code{isextended=0} ends the map. @node PAX 0 @appendixsubsec PAX Format, Versions 0.0 and 0.1 -@UNREVISED{} +@cindex sparse formats, v.0.0 There are two formats available in this branch. The version @code{0.0} is the initial version of sparse format used by @command{tar} versions 1.14--1.15.1. The sparse file map is kept in extended (@code{x}) PAX header variables: @table @code +@vrindex GNU.sparse.size, extended header variable @item GNU.sparse.size Real size of the stored file @item GNU.sparse.numblocks +@vrindex GNU.sparse.numblocks, extended header variable Number of blocks in the sparse map @item GNU.sparse.offset +@vrindex GNU.sparse.offset, extended header variable Offset of the data block @item GNU.sparse.numbytes +@vrindex GNU.sparse.numbytes, extended header variable Size of the data block @end table @@ -134,10 +142,13 @@ the @command{tar} implementation in question does not support POSIX format, it will also extract a file containing extension header attributes. This file can be used to expand the file to its original state. However, posix-aware @command{tar}s will usually ignore the -unknown variables, which makes restoring the file much more -difficult@FIXME-xref{how to extract sparse file using third-party @command{tar}s}. +unknown variables, which makes restoring the file more +difficult. @xref{extracting sparse v.0.x, Extraction of sparse +members in v.0.0 format}, for the detailed description of how to +restore such members using non-GNU @command{tar}s. @end enumerate +@cindex sparse formats, v.0.1 @GNUTAR{} 1.15.2 introduced sparse format version @code{0.1}, which attempted to solve these problems. As its predecessor, this format stores sparse map in the extended POSIX header. It retains @@ -147,6 +158,7 @@ it uses a single variable: @table @code @item GNU.sparse.map +@vrindex GNU.sparse.map, extended header variable Map of non-null data chunks. It is a string consisting of comma-separated values "@var{offset},@var{size}[,@var{offset-1},@var{size-1}...]" @end table @@ -158,6 +170,7 @@ is replaced with a special name, constructed using the following pattern: %d/GNUSparseFile.%p/%f @end smallexample +@vrindex GNU.sparse.name, extended header variable The real name of the sparse file is stored in the variable @code{GNU.sparse.name}. Thus, those @command{tar} implementations that are not aware of GNU extensions will at least extract the files @@ -171,8 +184,8 @@ header variable, this possibly can confuse some tars. @node PAX 1 @appendixsubsec PAX Format, Version 1.0 -@UNREVISED{} +@cindex sparse formats, v.1.0 The version @code{1.0} of sparse format was introduced with @GNUTAR{} 1.15.92. Its main objective was to make the resulting file extractable with little effort even by non-posix aware @command{tar} @@ -182,9 +195,11 @@ identify the format being used: @table @code @item GNU.sparse.major +@vrindex GNU.sparse.major, extended header variable Major version @item GNU.sparse.minor +@vrindex GNU.sparse.minor, extended header variable Minor version @end table @@ -195,6 +210,8 @@ constructed using the following pattern: %d/GNUSparseFile.%p/%f @end smallexample +@vrindex GNU.sparse.name, extended header variable, in v.1.0 +@vrindex GNU.sparse.realsize, extended header variable The real name of the sparse file is stored in the variable @code{GNU.sparse.name}. The real size of the file is stored in the variable @code{GNU.sparse.realsize}. @@ -211,7 +228,7 @@ The format is designed in such a way that non-posix aware tars and tars not supporting @code{GNU.sparse.*} keywords will extract each sparse file in its condensed form with the file map prepended and will place it into a separate directory. Then, using a simple program it would be -possible to expand the file to its original form even without GNU tar. -@FIXME-xref{how to extract sparse file using third-party -@command{tar}s}. @FIXME{Write the program and give its URL here}. +possible to expand the file to its original form even without @GNUTAR{}. +@xref{Sparse Recovery}, for the detailed information on how to extract +sparse members without @GNUTAR{}.