Frank Sorenson <sorenson@xxxxxxxxxx> writes:
Hi,
> Author: Frank Sorenson <sorenson@xxxxxxxxxx>
> Date: 2018-03-23 23:28:32 -0500
>
> fat: add function to truncate timestamps returned from fat_getattr
>
> vfat/msdos timestamps are stored on-disk with several different
> granularities, some of them lower resolution than timespec_trunc()
> can provide. However, they are only truncated as they are written
> to disk, so the timestamps in-memory for new or modified
> files/directories may be different from the same timestamps after
> a remount, as the now-truncated times are re-read from the on-disk
> format.
>
> This patch adds a function to adjust the timestamps returned from
> fat_getattr() so that userspace sees consistent times across a
> remount. The existing functions are used to convert the timespec
> to the on-disk representation, then back to timespec again.
>
> Signed-off-by: Frank Sorenson <sorenson@xxxxxxxxxx>
Already tried to use ->update_time() callback? With quick look though,
it seems to be possible to control timestamp granularity with
->update_time(), and add fat_current_time() or such to get proper
timestamp for FAT.
I think we should give consistent in-core inode timestamp too. For
example, overlayfs may be copy timestamps from in-core inode, etc., then
this stat workaround will not work.
Thanks.
> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> index 8fc1093da47d..0367be021b23 100644
> --- a/fs/fat/fat.h
> +++ b/fs/fat/fat.h
> @@ -410,6 +410,7 @@ extern void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec *ts,
> __le16 __time, __le16 __date, u8 time_cs);
> extern void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
> __le16 *time, __le16 *date, u8 *time_cs);
> +extern void fat_trunc_kstat_times(struct msdos_sb_info *sbi, struct kstat *stat);
> extern int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs);
>
> int fat_cache_init(void);
> diff --git a/fs/fat/file.c b/fs/fat/file.c
> index 4724cc9ad650..11639e393ef7 100644
> --- a/fs/fat/file.c
> +++ b/fs/fat/file.c
> @@ -370,6 +370,7 @@ int fat_getattr(const struct path *path, struct kstat *stat,
> {
> struct inode *inode = d_inode(path->dentry);
> generic_fillattr(inode, stat);
> + fat_trunc_kstat_times(MSDOS_SB(inode->i_sb), stat);
> stat->blksize = MSDOS_SB(inode->i_sb)->cluster_size;
>
> if (MSDOS_SB(inode->i_sb)->options.nfs == FAT_NFS_NOSTALE_RO) {
> diff --git a/fs/fat/misc.c b/fs/fat/misc.c
> index f9bdc1e01c98..52f40edefd12 100644
> --- a/fs/fat/misc.c
> +++ b/fs/fat/misc.c
> @@ -262,6 +262,29 @@ void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
> }
> EXPORT_SYMBOL_GPL(fat_time_unix2fat);
>
> +void fat_trunc_kstat_times(struct msdos_sb_info *sbi, struct kstat *stat)
> +{
> + if (stat->ino == MSDOS_ROOT_INO)
> + stat->mtime = stat->ctime = stat->atime =
> + (struct timespec){0, 0};
> + else {
> + __le16 time;
> + __le16 date;
> + u8 ctime_cs;
> +
> + fat_time_unix2fat(sbi, &stat->mtime, &time, &date, NULL);
> + fat_time_fat2unix(sbi, &stat->mtime, time, date, 0);
> +
> + fat_time_unix2fat(sbi, &stat->ctime, &time, &date,
> + sbi->options.isvfat ? &ctime_cs : NULL);
> + fat_time_fat2unix(sbi, &stat->ctime, time, date,
> + sbi->options.isvfat ? ctime_cs : 0);
> +
> + fat_time_unix2fat(sbi, &stat->atime, &time, &date, NULL);
> + fat_time_fat2unix(sbi, &stat->atime, 0, date, 0);
> + }
> +}
> +
> int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs)
> {
> int i, err = 0;
--
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
