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Fix truncate(2) mtime and ctime handling

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On Linux, ftruncate(2) always changes the file timestamps, even if the
file size is not changed. However, in case of a successfull
truncate(2), the timestamps are updated only if the file size changes.
This translates to the VFS calling the ZFS Posix Layer "setattr"
function (zpl_setattr) with ATTR_MTIME and ATTR_CTIME unconditionally
set on the iattr mask only when doing a ftruncate(2), while the
truncate(2) is left to the filesystem implementation to be dealt with.

This behaviour is consistent with POSIX:2004/SUSv3 specifications
where there's no explicit requirement for file size changes to update
the timestamps only for ftruncate(2):

http://pubs.opengroup.org/onlinepubs/009695399/functions/truncate.html
http://pubs.opengroup.org/onlinepubs/009695399/functions/ftruncate.html

This has been later updated in POSIX:2008/SUSv4 where, for both
truncate(2)/ftruncate(2), there's no mention of this size change
requirement:

http://austingroupbugs.net/view.php?id=489
http://pubs.opengroup.org/onlinepubs/9699919799/functions/truncate.html
http://pubs.opengroup.org/onlinepubs/9699919799/functions/ftruncate.html

Unfortunately the Linux VFS is still calling into the ZPL without
ATTR_MTIME/ATTR_CTIME set in the truncate(2) case: we fix this by
explicitly updating the timestamps when detecting the ATTR_SIZE bit,
which is always set in do_truncate(), on the iattr mask.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6811 
Closes #6819
This commit is contained in:
LOLi
2017-11-13 18:24:26 +01:00
committed by Brian Behlendorf
parent 13042a6ccd
commit 99834d1950
7 changed files with 221 additions and 4 deletions
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module/zfs/zfs_vnops.c
+2 -2
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@@ -3155,7 +3155,7 @@ top:
&atime, sizeof (atime));
}
if (mask & ATTR_MTIME) {
if (mask & (ATTR_MTIME | ATTR_SIZE)) {
ZFS_TIME_ENCODE(&vap->va_mtime, mtime);
ZTOI(zp)->i_mtime = timespec_trunc(vap->va_mtime,
ZTOI(zp)->i_sb->s_time_gran);
@@ -3164,7 +3164,7 @@ top:
mtime, sizeof (mtime));
}
if (mask & ATTR_CTIME) {
if (mask & (ATTR_CTIME | ATTR_SIZE)) {
ZFS_TIME_ENCODE(&vap->va_ctime, ctime);
ZTOI(zp)->i_ctime = timespec_trunc(vap->va_ctime,
ZTOI(zp)->i_sb->s_time_gran);