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bug#23397: 25.0.92; assertion failure auto-reverting a file being overwr
From: |
Lars Ingebrigtsen |
Subject: |
bug#23397: 25.0.92; assertion failure auto-reverting a file being overwritten |
Date: |
Sat, 05 Sep 2020 16:03:54 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
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
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Lars Ingebrigtsen <=