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New option --clamp-mtime

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The new `--clamp-mtime` option will change the behavior of `--mtime` to only
use the time specified if the file mtime is newer than the given time.
The `--clamp-mtime` option can only be used together with `--mtime`.

Typical use case is to make builds reproducible: to loose less
information, it's better to keep the original date of an archive, except for
files modified during the build process. In that case, using a reference
(and thus reproducible) timestamps for the latter is good enough. See
<https://wiki.debian.org/ReproducibleBuilds> for more information.

Patch submitted by Jeremy Bobbio and
Daniel Kahn Gillmor <dkg@fifthhorseman.net>

* doc/tar.1: Document --clamp-mtime
* doc/tar.texi: Likewise.

* src/common.h (set_mtime_option_mode): New enum
(set_mtime_option): Change type to enum set_mtime_option_mode.
(NEWER_OPTION_INITIALIZED): Rename to NEWER_OPTION_INITIALIZED.
* src/create.c (start_header): Set mtime depending on set_mtime_option.
* src/tar.c (options,parse_opt): New option --clamp-mtime
(decode_options): Initialize mtime_option

* tests/time02.at: New testcase.
* tests/Makefile.am: Add new testcase
* tests/testsuite.at: Likewise.
This commit is contained in:
Jeremy Bobbio
2016-03-24 07:11:28 +02:00
committed by Sergey Poznyakoff
parent 8d31493c99
commit 13d04fe6ae
9 changed files with 120 additions and 11 deletions
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5
doc/tar.1
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@@ -13,7 +13,7 @@
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with this program. If not, see <http://www.gnu.org/licenses/>.
.TH TAR 1 "March 16, 2016" "TAR" "GNU TAR Manual"
.TH TAR 1 "March 23, 2016" "TAR" "GNU TAR Manual"
.SH NAME
tar \- an archiving utility
.SH SYNOPSIS
@@ -1051,6 +1051,9 @@ Display progress messages every \fIN\fRth record (default 10).
\fB\-\-checkpoint\-action\fR=\fIACTION\fR
Run \fIACTION\fR on each checkpoint.
.TP
\fB\-\-clamp\-mtime\fR
Only set time when the file is more recent than what was given with \-\-mtime.
.TP
\fB\-\-full\-time\fR
Print file time to its full resolution.
.TP

21
doc/tar.texi
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@@ -2585,6 +2585,11 @@ complies to UNIX98, was introduced with version
writing the archive. This allows you to directly act on archives
while saving space. @xref{gzip}.
@opsummary{clamp-mtime}
@item --clamp-mtime
(See @option{--mtime}.)
@opsummary{confirmation}
@item --confirmation
@@ -2985,6 +2990,11 @@ either a textual date representation (@pxref{Date input formats}) or a
name of the existing file, starting with @samp{/} or @samp{.}. In the
latter case, the modification time of that file is used. @xref{override}.
When @command{--clamp-mtime} is also specified, files with
modification times earlier than @var{date} will retain their actual
modification times, and @var{date} will only be used for files whose
modification times are later than @var{date}.
@opsummary{multi-volume}
@item --multi-volume
@itemx -M
@@ -5445,6 +5455,17 @@ tar: Option --mtime: Treating date 'yesterday' as 2006-06-20
@dots{}
@end smallexample
@noindent
When used with @option{--clamp-mtime} @GNUTAR{} will only set the
modification date to @var{date} on files whose actual modification
date is later than @var{date}. This is to make it easy to build
reproducible archives given a common timestamp for generated files
while still retaining the original timestamps of untouched files.
@smallexample
$ @kbd{tar -c -f archive.tar --clamp-mtime --mtime=@atchar{}$SOURCE_DATE_EPOCH .}
@end smallexample
@item --owner=@var{user}
@opindex owner