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fat: ignore ctime updates, and keep ctime identical to mtime in memory

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FAT supports creation time but not change time, and there was no
corresponding timestamp for creation time in previous VFS.  The original
implementation took the compromise of saving the in-memory change time
into the on-disk creation time field, but this would lead to compatibility
issues with non-linux systems.

To address this issue, this patch changes the behavior of ctime.  It will
no longer be loaded and stored from the creation time on disk.  Instead of
that, it'll be consistent with the in-memory mtime and share the same
on-disk field.  All updates to mtime will also be applied to ctime in
memory, while all updates to ctime will be ignored.

Link: https://lkml.kernel.org/r/20220503152536.2503003-2-cccheng@synology.com
Signed-off-by: Chung-Chiang Cheng <cccheng@synology.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Chung-Chiang Cheng 2022-05-03 23:25:34 +08:00 committed by akpm
parent 4dcc3f96e7
commit 0f9d148167
2 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/fat/inode.c
View File

@ -567,12 +567,11 @@ int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
& ~((loff_t)sbi->cluster_size - 1)) >> 9;
fat_time_fat2unix(sbi, &inode->i_mtime, de->time, de->date, 0);
if (sbi->options.isvfat) {
fat_time_fat2unix(sbi, &inode->i_ctime, de->ctime,
de->cdate, de->ctime_cs);
inode->i_ctime = inode->i_mtime;
if (sbi->options.isvfat)
fat_time_fat2unix(sbi, &inode->i_atime, 0, de->adate, 0);
} else
fat_truncate_time(inode, &inode->i_mtime, S_ATIME|S_CTIME);
else
inode->i_atime = fat_truncate_atime(sbi, &inode->i_mtime);
return 0;
}
@ -888,8 +887,6 @@ retry:
&raw_entry->date, NULL);
if (sbi->options.isvfat) {
__le16 atime;
fat_time_unix2fat(sbi, &inode->i_ctime, &raw_entry->ctime,
&raw_entry->cdate, &raw_entry->ctime_cs);
fat_time_unix2fat(sbi, &inode->i_atime, &atime,
&raw_entry->adate, NULL);
}

9
fs/fat/misc.c
View File

@ -347,10 +347,13 @@ int fat_truncate_time(struct inode *inode, struct timespec64 *now, int flags)
if (flags & S_ATIME)
inode->i_atime = fat_truncate_atime(sbi, now);
if (flags & S_CTIME)
inode->i_ctime = fat_truncate_crtime(sbi, now);
/*
* ctime and mtime share the same on-disk field, and should be
* identical in memory. all mtime updates will be applied to ctime,
* but ctime updates are ignored.
*/
if (flags & S_MTIME)
inode->i_mtime = fat_truncate_mtime(sbi, now);
inode->i_mtime = inode->i_ctime = fat_truncate_mtime(sbi, now);
return 0;
}