From: Lars Ingebrigtsen <larsi@gnus.org>
To: Noam Postavsky <npostavs@gmail.com>
Cc: Ken Raeburn <raeburn@permabit.com>, 23397@debbugs.gnu.org
Subject: bug#23397: 25.0.92; assertion failure auto-reverting a file being overwritten
Date: Sat, 05 Sep 2020 16:03:54 +0200 [thread overview]
Message-ID: <87k0x848xh.fsf@gnus.org> (raw)
In-Reply-To: <87zhzutngf.fsf@gmail.com> (Noam Postavsky's message of "Sat, 16 Jun 2018 17:45:36 -0400")
Noam Postavsky <npostavs@gmail.com> writes:
> This seems to fix the scenario you gave in #17. I don't quite
> understand what the overlap expression is trying to compute though.
[...]
> + off_t file_end_pos = st.st_size;
[etc]
Eli Zaretskii <eliz@gnu.org> writes:
>> I don't quite understand what the overlap expression is trying to
>> compute though.
>
> It prevents us from re-using the same portion of buffer text for
> matching both at start and at end of the file. This could happen,
> e.g., with buffers whose contents is the same character, and a file
> whose contents is mostly the same, but larger, and with a few
> different characters in the middle. Then the "same_at_end" loop could
> inadvertently match a part of the buffer that was already matched by
> the "same_at_start" loop.
>
> The overlap expression computes the portion of the buffer that was
> matched by both "same_at_start" and "same_at_end" loops.
This was two years ago, but the patch doesn't seem to be applied? It
was a rather obscure timing-related (but serious) bug.
Noam, did Eli's explanation help?
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
prev parent reply other threads:[~2020-09-05 14:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-28 22:05 bug#23397: 25.0.92; assertion failure auto-reverting a file being overwritten Ken Raeburn
2016-05-02 16:47 ` Eli Zaretskii
2016-05-02 20:43 ` Ken Raeburn
2016-05-03 15:15 ` Eli Zaretskii
2016-05-03 21:04 ` Ken Raeburn
2018-06-16 21:45 ` Noam Postavsky
2018-06-17 5:36 ` Eli Zaretskii
2020-09-05 14:03 ` Lars Ingebrigtsen [this message]
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