On Fri, Apr 3, 2026 at 11:50 AM Tom Lane <[email protected]> wrote: > > How about using --format=ustar, instead of that sparse control stuff? > > I did it that way for GNU tar, but did not research whether bsdtar > will take that option. Feel free to hack on ebba64c08 some more. > > (It seems though that the two tars' locutions for "write to stdout" > are different, so we might have to have separate tests even if they > end up pushing the same option.)
I have: $ tar --version bsdtar 3.8.2 - libarchive 3.8.2 zlib/1.3.1 liblzma/5.8.1 libzstd/1.5.2 openssl/3.5.4 libb2/bundled $ gtar --version tar (GNU tar) 1.35 Copyright (C) 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by John Gilmore and Jay Fenlason. This seems to work for both: $ tar --format=ustar -c /dev/null > /dev/null tar: Removing leading '/' from member names $ gtar --format=ustar -c /dev/null > /dev/null gtar: Removing leading `/' from member names The attached passes with both, and regress_log_001_basic looks like: # Running: /usr/bin/tar --format=ustar -cf /tmp/J_ifbfUOSd/pg_wal.tar archive_status 000000010000000000000001 000000010000000000000003 000000010000000000000002 summaries [12:12:24.301](0.072s) ok 101 # Running: /usr/local/bin/gtar --format=ustar -cf /tmp/pbdsHdrAdw/pg_wal.tar 000000010000000000000002 archive_status 000000010000000000000003 summaries 000000010000000000000001 [12:18:14.739](0.050s) ok 101 I think a Windows system could be using either. BSD tar comes pre-installed by Microsoft and people often install GNU tools. So I think we should use File::Spec->devnull() instead of /dev/null, and Andrew showed that working. I doubt Windows is capable of making sparse files (except perhaps with ReFS?), but it's nice to use the same code everywhere and future-proof in case GNU carries out its thread to switch to pax by default. Windows probably has file attributes that ustar can't represent (?), so I guess that might motivate it to use pax headers if they are indeed added only when needed. Longer term I think we need to tolerate but ignore pax headers. If I understand the spirit of this long evolution, pax archives are intended to be acceptable to pre-pax implementations, which implies that they can't really change the meaning of the bits of the file contents. That's why GNU's --sparse hides funky file encodings from old tars by renaming them to GNUSparseFile.%p/%f, and that leads back to my original suggestion that we should figure out how to detect and reject pax only if we failed to find the file under the expected name. (Or of course we could just implement support for that, and I have a half-baked trial patch for that but now is not the time.)
From 0635c0106946ce76c1bb84a5c17b71d0b0e574f7 Mon Sep 17 00:00:00 2001 From: Thomas Munro <[email protected]> Date: Fri, 3 Apr 2026 12:03:56 +1300 Subject: [PATCH] Harmonize tar option tests from ebba64c0. * GNU and BSD tar both understand --format=ustar. * Windows lacks /dev/null, but perl knows its local name. Discussion: https://postgr.es/m/3676229.1775170250%40sss.pgh.pa.us Backpatch-through: 18 --- src/test/perl/PostgreSQL/Test/Utils.pm | 15 ++++----------- 1 file changed, 4 insertions(+), 11 deletions(-) diff --git a/src/test/perl/PostgreSQL/Test/Utils.pm b/src/test/perl/PostgreSQL/Test/Utils.pm index 120999f6ac9..05e1698efa6 100644 --- a/src/test/perl/PostgreSQL/Test/Utils.pm +++ b/src/test/perl/PostgreSQL/Test/Utils.pm @@ -1328,21 +1328,14 @@ sub tar_portability_options # GNU tar typically produces gnu-format archives, which we can read fine. # But some platforms configure it to default to posix/pax format, and - # apparently they enable --sparse too. Override that. - if (system("$tar --format=ustar -c -O /dev/null >/dev/null 2>/dev/null") + # apparently they enable --sparse too. BSD tar does something similar. + # Override that. + my $devnull = File::Spec->devnull(); + if (system("$tar --format=ustar -c $devnull >$devnull 2>$devnull") == 0) { push(@tar_p_flags, "--format=ustar"); } - - # bsdtar also archives sparse files by default, but it spells the switch - # to disable that differently. - if (system("$tar --no-read-sparse -c - /dev/null >/dev/null 2>/dev/null") - == 0) - { - push(@tar_p_flags, "--no-read-sparse"); - } - return @tar_p_flags; } -- 2.53.0
