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Avoid file time stamp bug on MS-Windows.

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* fileio.c (Fwrite_region): Don't use the heuristic on empty files,
as FAT32 doesn't update time stamps when truncating them.
Also, check that a file time stamp is not a multiple of 100 ns;
this should catch all instances of the problem on MS-Windows,
as its native file system resolution is 100 ns or worse, and
checking for a non-multiple of 100 ns should impose only a small
overhead on systems with ns resolution.

Fixes: debbugs:13149
This commit is contained in:
Paul Eggert 2013-02-02 11:18:00 -08:00
parent e7ac588e19
commit 8ea41ea996
2 changed files with 26 additions and 4 deletions
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11
src/ChangeLog
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@ -1,3 +1,14 @@
2013-02-02 Paul Eggert <eggert@cs.ucla.edu>
Avoid file time stamp bug on MS-Windows (Bug#13149).
* fileio.c (Fwrite_region): Don't use the heuristic on empty files,
as FAT32 doesn't update time stamps when truncating them.
Also, check that a file time stamp is not a multiple of 100 ns;
this should catch all instances of the problem on MS-Windows,
as its native file system resolution is 100 ns or worse, and
checking for a non-multiple of 100 ns should impose only a small
overhead on systems with ns resolution.
2013-02-02 Eli Zaretskii <eliz@gnu.org>
Avoid encoding file names on MS-Windows when they need to be run

19
src/fileio.c
View file

@ -5020,11 +5020,22 @@ This calls `write-region-annotate-functions' at the start, and
if (fstat (desc1, &st1) == 0
&& st.st_dev == st1.st_dev && st.st_ino == st1.st_ino)
{
/* Use the heuristic if it appears to be valid. With neither
O_EXCL nor O_TRUNC, if Emacs happened to write nothing to the
file, the time stamp won't change. Also, some non-POSIX
systems don't update an empty file's time stamp when
truncating it. Finally, file systems with 100 ns or worse
resolution sometimes seem to have bugs: on a system with ns
resolution, checking ns % 100 incorrectly avoids the heuristic
1% of the time, but the problem should be temporary as we will
try again on the next time stamp. */
bool use_heuristic
= ((open_flags & (O_EXCL | O_TRUNC)) != 0
&& st.st_size != 0
&& EMACS_NSECS (modtime) % 100 != 0);
EMACS_TIME modtime1 = get_stat_mtime (&st1);
/* If neither O_EXCL nor O_TRUNC is used, and Emacs happened to
write nothing to the file, the file's time stamp won't change
so it should not be used in this heuristic. */
if ((open_flags & (O_EXCL | O_TRUNC)) != 0
if (use_heuristic
&& EMACS_TIME_EQ (modtime, modtime1)
&& st.st_size == st1.st_size)
{