From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com> To: "SZEDER Gábor" <szeder.dev@gmail.com> Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>, Sebastian Staudt <koraktor@gmail.com>, Josh Steadmon <steadmon@google.com>, Johannes Schindelin <Johannes.Schindelin@gmx.de> Subject: Re: [PATCH 2/2] commit-graph tests: fix cryptic unportable "dd" invocation Date: Thu, 21 Feb 2019 23:26:26 +0100 Message-ID: <878sy86anh.fsf@evledraar.gmail.com> (raw) In-Reply-To: <20190221204310.GS1622@szeder.dev> On Thu, Feb 21 2019, SZEDER Gábor wrote: > On Thu, Feb 21, 2019 at 08:28:49PM +0100, Ævar Arnfjörð Bjarmason wrote: >> Change an unportable invocation of "dd" that truncated the >> commit-graph to call Perl's truncate() function instead. >> >> In POSIX it is unspecified what happens when count=0 is >> provided[1]. The NetBSD "dd" behavior differs from GNU (and seemingly >> other BSDs), which as left this test broken since >> d2b86fbaa1 ("commit-graph: fix buffer read-overflow", 2019-01-15). >> >> In POSIX the truncate(2) and ftruncate(2) functions are >> portable. We've used the latter since 271421cd34 ("Update partial HTTP >> transfers.", 2005-09-30), but the truncate(1) command-line tool is >> GNU-specific. Thus let's use Perl's version of it. We could also just >> introduce a "test-tool truncate" in the future if we wanted to avoid >> shelling out to perl. >> >> On Linux and NetBSD we don't need the "if -s $ARGV[0] > $ARGV[1]" >> condition I'm adding. We never have a $zero_pos longer than the file >> being truncated. But let's have that condition to future-proof the >> code, and because "the behavior is undefined if LENGTH is greater than >> the length of the file" (perldoc -f truncate). >> >> 1. http://pubs.opengroup.org/onlinepubs/9699919799/utilities/dd.html >> >> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> >> --- >> t/t5318-commit-graph.sh | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh >> index d4bd1522fe..d99bea6cce 100755 >> --- a/t/t5318-commit-graph.sh >> +++ b/t/t5318-commit-graph.sh >> @@ -382,7 +382,8 @@ corrupt_graph_and_verify() { >> test_when_finished mv commit-graph-backup $objdir/info/commit-graph && >> cp $objdir/info/commit-graph commit-graph-backup && >> printf "$data" | dd of="$objdir/info/commit-graph" bs=1 seek="$pos" conv=notrunc && >> - dd of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" count=0 && >> + perl -we 'truncate $ARGV[0], $ARGV[1] if -s $ARGV[0] > $ARGV[1]' \ >> + $objdir/info/commit-graph $zero_pos && > > This will make Dscho unhappy :) Sorry Dscho :) Although this is a one-off in one test, as opposed to a new "perl -e" in test-lib-functions.sh > Is there a problem with: > > dd if=/dev/null of="$objdir/info/commit-graph" bs=1 seek="$zero_pos" > > ? > > To my understanding of the specs it's well-defined what it should do, > even when $zero_pos is larget than the file size, it's shorter, > simpler, and doesn't introduce yet another Perl dependency. I tried that as a one-off and it indeed works as a "truncate" on NetBSD & GNU. My reading of POSIX "dd" and "lseek" docs is that we'd need some similar guard if we're going to be paranoid about a $zero_pos value past the end of the file. It doesn't look like that's portable, my assumption from reading the docs is that the seek=* will devolve without a stat() check on some "dd" implementations to an "lseek". I'm not going to submit a re-roll of this because it works, and I'd still trust Perl's truncate(...) portability over dd. But more importantly because it takes me *ages* to fully re-test anything on the slow BSD VMs I have access to, and I already tore town my one-off hacking env there after testing these patches... >> generate_zero_bytes $(($orig_size - $zero_pos)) >>"$objdir/info/commit-graph" && >> test_must_fail git commit-graph verify 2>test_err && >> grep -v "^+" test_err >err && >> -- >> 2.21.0.rc0.258.g878e2cd30e >>
next prev parent reply other threads:[~2019-02-21 22:26 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-19 23:29 [ANNOUNCE] Git v2.21.0-rc2 Junio C Hamano 2019-02-20 0:43 ` Randall S. Becker 2019-02-20 19:41 ` Junio C Hamano 2019-02-20 20:46 ` Johannes Schindelin 2019-02-21 13:10 ` Duy Nguyen 2019-02-21 23:55 ` brian m. carlson 2019-02-22 9:13 ` Duy Nguyen 2019-02-21 15:54 ` Randall S. Becker 2019-02-21 20:04 ` Junio C Hamano 2019-02-21 21:06 ` SZEDER Gábor 2019-02-21 21:30 ` Randall S. Becker 2019-02-21 19:59 ` Randall S. Becker 2019-02-21 10:46 ` Git for Windows v2.21.0-rc2, was " Johannes Schindelin 2019-02-21 19:28 ` [PATCH 0/2] BSD portability fixes for 2.21.0-rc2 Ævar Arnfjörð Bjarmason 2019-02-22 0:37 ` Josh Steadmon 2019-02-21 19:28 ` [PATCH 1/2] tests: fix unportable "\?" and "\+" regex syntax Ævar Arnfjörð Bjarmason 2019-02-22 5:00 ` Junio C Hamano 2019-02-21 19:28 ` [PATCH 2/2] commit-graph tests: fix cryptic unportable "dd" invocation Ævar Arnfjörð Bjarmason 2019-02-21 20:43 ` SZEDER Gábor 2019-02-21 22:26 ` Ævar Arnfjörð Bjarmason [this message] 2019-02-22 10:50 ` SZEDER Gábor 2019-02-22 14:34 ` Ævar Arnfjörð Bjarmason 2019-02-22 18:30 ` Junio C Hamano 2019-02-22 18:35 ` Todd Zullinger 2019-02-22 19:23 ` [PATCH v3] commit-graph tests: fix " Junio C Hamano
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