From: "SZEDER Gábor" <szeder.dev@gmail.com> To: "Ævar Arnfjörð Bjarmason" <avarab@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: Fri, 22 Feb 2019 11:50:53 +0100 Message-ID: <20190222105053.GU1622@szeder.dev> (raw) In-Reply-To: <878sy86anh.fsf@evledraar.gmail.com> On Thu, Feb 21, 2019 at 11:26:26PM +0100, Ævar Arnfjörð Bjarmason wrote: > >> - 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". Could you point to the part of the specs where your assumption comes from? The specs are quite clear on what should happen: If the size of the seek plus the size of the input file is less than the previous size of the output file, the output file shall be shortened by the copy. If the input file is empty and either the size of the seek is greater than the previous size of the output file or the output file did not previously exist, the size of the output file shall be set to the file offset after the seek. IOW no such guard is necessary. I checked the man pages of FreeBSD's, NetBSD's, OpenBSD's and Solaris' 'dd', and they are clearly following the specs in this respect. I tried NetBSD 6.0's and 8.0's 'dd', and both behave as advertised. And using 'dd' doesn't add a condition after statement... > 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:[~2019-02-22 10:51 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 2019-02-22 10:50 ` SZEDER Gábor [this message] 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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