Commit 0f9d1481 authored by Chung-Chiang Cheng's avatar Chung-Chiang Cheng Committed by Andrew Morton
Browse files

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

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: default avatarChung-Chiang Cheng <cccheng@synology.com>
Acked-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4dcc3f96

fs/fat/inode.c

+4 −7
Original line number Diff line number Diff line
@@ -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 @@ static int __fat_write_inode(struct inode *inode, int wait) 
			  &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);

	}

fs/fat/misc.c

+6 −3
Original line number Diff line number Diff line
@@ -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;

}