From: Junio C Hamano <gitster@pobox.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>,
Johannes Schindelin <johannes.schindelin@gmx.de>,
Jonathan Nieder <jrnieder@gmail.com>
Subject: Re: [PATCH v2 1/5] Makefile: rename objects in-place, don't clobber
Date: Mon, 29 Mar 2021 11:21:52 -0700 [thread overview]
Message-ID: <xmqqy2e5kegv.fsf@gitster.g> (raw)
In-Reply-To: <patch-1.6-3330cdbccc0-20210329T161723Z-avarab@gmail.com> (=?utf-8?B?IsOGdmFyCUFybmZqw7Zyw7A=?= Bjarmason"'s message of "Mon, 29 Mar 2021 18:20:08 +0200")
Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
> Per the log of changes to the Makfile and Junio's recent comment about
> [1] why that pattern got introduced it was for a different reason
> entirely, i.e. ("[]" edits are mine, for brevity):
>
> [T]hat age old convention [...] is spelled [as]:
>
> thing:
> rm -f thing thing+
> prepare contents for thing >thing+
Did I say that? I recall I specifically avoided the "redirection"
because this is *NOT* shell-script only principle. If a command is
so broken that "cmd -o thing" that fails to work correctly leaves a
broken output in thing, then the pattern should be applied and made
to "cmd -o thing+ && mv thing+ thing".
On the other hand, if "cmd" refrains from leaving a half-baked
result in "-o thing" (and I believe $(CC) is well-behaved even on
AIX), I do not think it is a good idea to use that pattern. One
version of AIX may refuse to overwrite a file in use because
creat("thing") that is necessary for "-o thing" may fail while
"thing" is in use), but another system may refuse to rename over a
file in use (i.e. "-o thing+" into a brand new "thing+" may be OK
but the final "mv thing+ thing" may fail). So pretending that it is
a cure for broken use case is cluttering Makefile for no real
benefit and leading readers into confused thinking.
> mv thing+ thing
>
> It protects us from a failure mode where "prepare contents for
> thing" step is broken and leaves a "thing" that does not work, but
> confuses make that make does not need to rebuild it, if you wrote it
> as such:
>
> thing:
> prepare contents for thing >thing
>
> [It might leave behind a corrupt 'thing'.] In any case, it is not
> "we are trying to make thing available while it is being
> rewritten" at all.
>
> That makes perfect sense for shellscripts, but as this change shows
> there's other good reasons to use this age old convention that weren't
> considered at the time.
So, no, the age old convention may have considered and does not
apply to such a use case.
> git$X: git.o GIT-LDFLAGS $(BUILTIN_OBJS) $(GITLIBS)
> - $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
> - $(filter %.o,$^) $(LIBS)
> + $(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@+ $(ALL_LDFLAGS) \
> + $(filter %.o,$^) $(LIBS) && \
> + mv $@+ $@
Really, does anybody else use "$(CC) -o $@" in such a way in their
Makefile? Having to do this smells simply crazy (I am not saying
you are crazy---the platform that forces you to write such a thing
is crazy).
So, while I do not think the end result would break the build (other
than it probably would leave crufts "make clean" would not notice
behind when interrupted in the middle), I am moderately negative on
this change.
Thanks.
next prev parent reply other threads:[~2021-03-29 18:22 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-07 13:20 [PATCH] Makefile: generate 'git' as 'cc [...] -o git+ && mv git+ git' Ævar Arnfjörð Bjarmason
2021-03-07 20:41 ` Junio C Hamano
2021-03-08 12:38 ` Ævar Arnfjörð Bjarmason
2021-03-08 17:21 ` Junio C Hamano
2021-03-08 18:26 ` Jeff King
2021-03-29 16:20 ` [PATCH v2 0/5] Makefile: don't die on AIX with open ./git Ævar Arnfjörð Bjarmason
2021-03-29 16:20 ` [PATCH v2 1/5] Makefile: rename objects in-place, don't clobber Ævar Arnfjörð Bjarmason
2021-03-29 18:21 ` Junio C Hamano [this message]
2021-03-29 18:26 ` Junio C Hamano
2021-03-29 23:24 ` Ævar Arnfjörð Bjarmason
2021-03-30 0:21 ` Junio C Hamano
2021-03-31 14:17 ` Ævar Arnfjörð Bjarmason
2021-03-31 18:50 ` Junio C Hamano
2021-03-29 16:20 ` [PATCH v2 2/5] Makefile: rename scripts " Ævar Arnfjörð Bjarmason
2021-03-29 18:40 ` Junio C Hamano
2021-03-29 23:28 ` Ævar Arnfjörð Bjarmason
2021-03-29 16:20 ` [PATCH v2 3/5] Makefile: don't needlessly "rm $@ $@+" before "mv $@+ $@" Ævar Arnfjörð Bjarmason
2021-03-29 18:46 ` Junio C Hamano
2021-03-29 16:20 ` [PATCH v2 4/5] Makefile: add the ".DELETE_ON_ERROR" flag Ævar Arnfjörð Bjarmason
2021-03-29 18:51 ` Junio C Hamano
2021-03-29 23:31 ` Ævar Arnfjörð Bjarmason
2021-03-29 23:58 ` Junio C Hamano
2021-03-30 15:11 ` Jeff King
2021-03-30 18:36 ` Junio C Hamano
2021-03-31 6:58 ` Jeff King
2021-03-31 18:36 ` Junio C Hamano
2021-03-31 22:29 ` Johannes Schindelin
2021-03-29 16:20 ` [PATCH v2 5/5] Makefile: don't "rm configure" before generating it Ævar Arnfjörð Bjarmason
2021-03-29 16:31 ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Ævar Arnfjörð Bjarmason
2021-03-29 16:31 ` [PATCH 1/6] Makefile: symlink the same way under "symlinks" and "no hardlinks" Ævar Arnfjörð Bjarmason
2021-03-29 22:17 ` Junio C Hamano
2021-03-29 16:31 ` [PATCH 2/6] Makefile: begin refactoring out "ln || ln -s || cp" pattern Ævar Arnfjörð Bjarmason
2021-03-29 22:20 ` Junio C Hamano
2021-03-29 16:31 ` [PATCH 3/6] Makefile: refactor " Ævar Arnfjörð Bjarmason
2021-03-29 22:24 ` Junio C Hamano
2021-03-30 15:20 ` Jeff King
2021-03-30 18:36 ` Junio C Hamano
2021-03-29 16:31 ` [PATCH 4/6] Makefile: make INSTALL_SYMLINKS affect the build directory Ævar Arnfjörð Bjarmason
2021-03-29 22:31 ` Junio C Hamano
2021-03-31 14:04 ` Ævar Arnfjörð Bjarmason
2021-03-29 16:31 ` [PATCH 5/6] Makefile: use "ln -f" instead of "rm && ln" Ævar Arnfjörð Bjarmason
2021-03-29 22:46 ` Junio C Hamano
2021-03-29 16:31 ` [PATCH 6/6] Makefile: add a INSTALL_FALLBACK_LN_CP mode Ævar Arnfjörð Bjarmason
2021-03-29 22:53 ` Junio C Hamano
2021-03-31 14:03 ` Ævar Arnfjörð Bjarmason
2021-03-31 18:45 ` Junio C Hamano
2021-03-31 19:01 ` Ævar Arnfjörð Bjarmason
2021-03-29 23:08 ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Junio C Hamano
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