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Improve reproducibility recipe

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* doc/tar.texi (Reproducibility): Improve index.
Improve and add comments to recipe.  In the recipe,
don’t worry about file names beginning with ‘-’ for simplicity;
don’t use touch -c as it exits with status 0 even when it
does not work; and set directory timestamps too.
This commit is contained in:
Paul Eggert
2023-07-25 09:43:57 -07:00
parent 8ed95e92ef
commit 68636f0bcb
1 changed files with 20 additions and 8 deletions
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doc/tar.texi
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@@ -10307,6 +10307,7 @@ This option is meaningless with @option{--list} (@option{-t}).
@node Portability @node Portability
@section Making @command{tar} Archives More Portable @section Making @command{tar} Archives More Portable
@cindex portable archives
Creating a @command{tar} archive on a particular system that is meant to be Creating a @command{tar} archive on a particular system that is meant to be
useful later on many other machines and with other versions of @command{tar} useful later on many other machines and with other versions of @command{tar}
is more challenging than you might think. @command{tar} archive formats is more challenging than you might think. @command{tar} archive formats
@@ -11182,6 +11183,7 @@ Done
@node Reproducibility @node Reproducibility
@section Making @command{tar} Archives More Reproducible @section Making @command{tar} Archives More Reproducible
@cindex reproducible archives
Sometimes it is important for an archive to be @dfn{reproducible}, Sometimes it is important for an archive to be @dfn{reproducible},
so that one can be easily verify it to have been derived solely from so that one can be easily verify it to have been derived solely from
its input. We call an archive reproducible, if an archive its input. We call an archive reproducible, if an archive
@@ -11256,11 +11258,23 @@ function get_commit_time() @{
--date=format:%Y-%m-%dT%H:%M:%SZ \ --date=format:%Y-%m-%dT%H:%M:%SZ \
"$@@" "$@@"
@} @}
SOURCE_EPOCH=$(get_commit_time) #
# Set each source file timestamp to that of its latest commit.
git ls-files | while read -r file; do git ls-files | while read -r file; do
commit_time=$(get_commit_time -- "$file") && commit_time=$(get_commit_time "$file") &&
touch -cmd $commit_time -- "$file" touch -md $commit_time "$file"
done done
#
# Set timestamp of each directory under $FILES
# to the latest timestamp of any descendant.
find $FILES -depth -type d -exec sh -c \
'touch -r "$0/$(ls -At "$0" | head -n 1)" "$0"' \
@{@} ';'
#
# Create $ARCHIVE.tgz from $FILES, pretending that
# the modification time for each newer file
# is that of the most recent commit of any source file.
SOURCE_EPOCH=$(get_commit_time)
TARFLAGS=" TARFLAGS="
--sort=name --format=posix --sort=name --format=posix
--pax-option=exthdr.name=%d/PaxHeaders/%f --pax-option=exthdr.name=%d/PaxHeaders/%f
@@ -11269,11 +11283,9 @@ TARFLAGS="
--numeric-owner --owner=0 --group=0 --numeric-owner --owner=0 --group=0
--mode=go+u,go-w --mode=go+u,go-w
" "
GZIPFLAGS=" GZIPFLAGS="--no-name --best"
--no-name --best LC_ALL=C tar $TARFLAGS -cf - $FILES |
" gzip $GZIPFLAGS > $ARCHIVE.tgz
LC_ALL=C tar $TARFLAGS -cf - FILES |
gzip $GZIPFLAGS > ARCHIVE.tgz
@end example @end example
@node cpio @node cpio