From: Jeff King <peff@peff.net>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: demerphq <demerphq@gmail.com>, Git <git@vger.kernel.org>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH 3/7] avoid "write_in_full(fd, buf, len) != len" pattern
Date: Thu, 14 Sep 2017 20:42:37 -0400 [thread overview]
Message-ID: <20170915004237.wjys6tgyxk6j43op@sigill.intra.peff.net> (raw)
In-Reply-To: <20170913211430.GK27425@aiede.mtv.corp.google.com>
On Wed, Sep 13, 2017 at 02:14:30PM -0700, Jonathan Nieder wrote:
> > I really wish every "write_in_full()" user would just
> > check against "<0" now, but this fixes the nasty and
> > stupid ones.
>
> Ok, you convinced me.
>
> Should we add a comment to cache.h as well encouraging this?
I'd be OK with a comment, though I don't know that it's strictly
necessary. It looks like most of it was just cargo-culted, so removing
the offending examples is sufficient.
> > [1] A careful reader may notice there is one way that
> > write_in_full() can return a different value. If we ask
> > write() to write N bytes and get a return value that is
> > _larger_ than N, we could return a larger total. But
> > besides the fact that this would imply a totally broken
> > version of write(), it would already invoke undefined
> > behavior. Our internal remaining counter is an unsigned
> > size_t, which means that subtracting too many byte will
> > wrap it around to a very large number. So we'll instantly
> > begin reading off the end of the buffer, trying to write
> > gigabytes (or petabytes) of data.
>
> This footnote just leaves me more confused, since as you mention,
> write() never would return a value greater than N. Are you saying we
> need to defend against a broken platform where that isn't true?
No, I'm saying that my claim that write_in_full() can only return two
values (-1 and the original length) is not strictly true. But that it
doesn't matter in practice.
I don't think we need to defend against such a broken platform, but I
didn't want anybody reading the claim to say "aha, you forgot this
case". It is a case that does not matter.
-Peff
next prev parent reply other threads:[~2017-09-15 0:42 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-13 11:59 Bug: git branch --unset-upstream command can nuke config when disk is full demerphq
2017-09-13 12:34 ` Jeff King
2017-09-13 13:38 ` demerphq
2017-09-13 14:17 ` Jeff King
2017-09-13 14:49 ` demerphq
2017-09-13 14:51 ` Jeff King
2017-09-13 15:18 ` demerphq
2017-09-13 15:22 ` Jeff King
2017-09-13 15:49 ` demerphq
2017-09-13 17:08 ` [PATCH 0/7] config.c may fail to notice some write() failures Jeff King
2017-09-13 17:11 ` [PATCH 1/7] config: avoid "write_in_full(fd, buf, len) < len" pattern Jeff King
2017-09-13 17:47 ` Jonathan Nieder
2017-09-13 17:53 ` Jeff King
2017-09-13 17:59 ` Jonathan Nieder
2017-09-13 18:11 ` Jeff King
2017-09-13 18:15 ` [PATCH v2] " Jeff King
2017-09-13 18:24 ` Jonathan Nieder
2017-09-13 18:58 ` Jeff King
2017-09-13 19:18 ` Jonathan Nieder
2017-09-13 19:49 ` Jonathan Nieder
2017-09-13 22:43 ` Ramsay Jones
2017-09-13 23:31 ` Ramsay Jones
2017-09-15 0:37 ` Jeff King
2017-09-15 15:15 ` Ramsay Jones
2017-09-13 21:33 ` Junio C Hamano
2017-09-13 17:11 ` [PATCH 2/7] get-tar-commit-id: check write_in_full() return against 0 Jeff King
2017-09-13 17:53 ` Jonathan Nieder
2017-09-13 18:02 ` Jeff King
2017-09-13 18:37 ` Jeff King
2017-09-13 21:09 ` Jonathan Nieder
2017-09-15 0:40 ` Jeff King
2017-09-13 17:16 ` [PATCH 3/7] avoid "write_in_full(fd, buf, len) != len" pattern Jeff King
2017-09-13 21:14 ` Jonathan Nieder
2017-09-15 0:42 ` Jeff King [this message]
2017-09-13 17:16 ` [PATCH 4/7] convert less-trivial versions of "write_in_full() != len" Jeff King
2017-09-13 21:16 ` Jonathan Nieder
2017-09-13 17:17 ` [PATCH 5/7] pkt-line: check write_in_full() errors against "< 0" Jeff King
2017-09-13 21:17 ` Jonathan Nieder
2017-09-13 17:17 ` [PATCH 6/7] notes-merge: use ssize_t for write_in_full() return value Jeff King
2017-09-13 21:20 ` Jonathan Nieder
2017-09-15 0:43 ` Jeff King
2017-09-13 17:17 ` [PATCH 7/7] config: flip return value of store_write_*() Jeff King
2017-09-13 21:25 ` Jonathan Nieder
2017-09-15 0:46 ` Jeff King
2017-09-13 18:47 ` [PATCH 8/7] read_pack_header: handle signed/unsigned comparison in read result Jeff King
2017-09-13 19:11 ` Jonathan Nieder
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