OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx> 於 2022年3月22日 週二 下午3:33寫道：
>
> Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx> writes:
>
> > In the old days, FAT supports creation time, but there's no corresponding
> > timestamp in VFS. The implementation mixed the meaning of change time and
> > creation time into a single ctime field.
> >
> > This patch introduces a new field for creation time, and reports it in
> > statx. The original ctime doesn't stand for create time any more. All
> > the behaviors of ctime (change time) follow mtime, as exfat does.
>
> Yes, ctime is issue (include compatibility issue when changing) from
> original author of this driver. And there is no perfect solution and
> subtle issue I think.
>
> I'm not against about this change though, this behavior makes utimes(2)
> behavior strange, e.g. user can change ctime, but FAT forget it anytime,
> because FAT can't save it.
>
> Did you consider about those behavior and choose this?
Yes. I think it's not perfect but a better choice to distinguish between
change-time and creation-time. While change-time is no longer saved to
disk, the new behavior maintains the semantic of "creation" and is more
compatible with non-linux systems.
Thanks.
> Thanks.
>
> > Signed-off-by: Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx>
> > ---
> > fs/fat/fat.h | 1 +
> > fs/fat/file.c | 6 ++++++
> > fs/fat/inode.c | 15 ++++++++++-----
> > fs/fat/misc.c | 6 +++---
> > 4 files changed, 20 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> > index 508b4f2a1ffb..e4409ee82ea9 100644
> > --- a/fs/fat/fat.h
> > +++ b/fs/fat/fat.h
> > @@ -126,6 +126,7 @@ struct msdos_inode_info {
> > struct hlist_node i_fat_hash; /* hash by i_location */
> > struct hlist_node i_dir_hash; /* hash by i_logstart */
> > struct rw_semaphore truncate_lock; /* protect bmap against truncate */
> > + struct timespec64 i_crtime; /* File creation (birth) time */
> > struct inode vfs_inode;
> > };
> >
> > diff --git a/fs/fat/file.c b/fs/fat/file.c
> > index 13855ba49cd9..184fa0375152 100644
> > --- a/fs/fat/file.c
> > +++ b/fs/fat/file.c
> > @@ -405,6 +405,12 @@ int fat_getattr(struct user_namespace *mnt_userns, const struct path *path,
> > /* Use i_pos for ino. This is used as fileid of nfs. */
> > stat->ino = fat_i_pos_read(MSDOS_SB(inode->i_sb), inode);
> > }
> > +
> > + if (request_mask & STATX_BTIME) {
> > + stat->result_mask |= STATX_BTIME;
> > + stat->btime = MSDOS_I(inode)->i_crtime;
> > + }
> > +
> > return 0;
> > }
> > EXPORT_SYMBOL_GPL(fat_getattr);
> > diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> > index a6f1c6d426d1..41b85b95ee9d 100644
> > --- a/fs/fat/inode.c
> > +++ b/fs/fat/inode.c
> > @@ -566,12 +566,15 @@ 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);
> > + inode->i_ctime = inode->i_mtime;
> > if (sbi->options.isvfat) {
> > - fat_time_fat2unix(sbi, &inode->i_ctime, de->ctime,
> > - de->cdate, de->ctime_cs);
> > fat_time_fat2unix(sbi, &inode->i_atime, 0, de->adate, 0);
> > - } else
> > - fat_truncate_time(inode, &inode->i_mtime, S_ATIME|S_CTIME);
> > + fat_time_fat2unix(sbi, &MSDOS_I(inode)->i_crtime, de->ctime,
> > + de->cdate, de->ctime_cs);
> > + } else {
> > + fat_truncate_atime(sbi, &inode->i_mtime, &inode->i_atime);
> > + fat_truncate_crtime(sbi, &inode->i_mtime, &MSDOS_I(inode)->i_crtime);
> > + }
> >
> > return 0;
> > }
> > @@ -756,6 +759,8 @@ static struct inode *fat_alloc_inode(struct super_block *sb)
> > ei->i_logstart = 0;
> > ei->i_attrs = 0;
> > ei->i_pos = 0;
> > + ei->i_crtime.tv_sec = 0;
> > + ei->i_crtime.tv_nsec = 0;
> >
> > return &ei->vfs_inode;
> > }
> > @@ -887,7 +892,7 @@ 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,
> > + fat_time_unix2fat(sbi, &MSDOS_I(inode)->i_crtime, &raw_entry->ctime,
> > &raw_entry->cdate, &raw_entry->ctime_cs);
> > fat_time_unix2fat(sbi, &inode->i_atime, &atime,
> > &raw_entry->adate, NULL);
> > diff --git a/fs/fat/misc.c b/fs/fat/misc.c
> > index c87df64f8b2b..36b6da6461cc 100644
> > --- a/fs/fat/misc.c
> > +++ b/fs/fat/misc.c
> > @@ -341,10 +341,10 @@ int fat_truncate_time(struct inode *inode, struct timespec64 *now, int flags)
> >
> > if (flags & S_ATIME)
> > fat_truncate_atime(sbi, now, &inode->i_atime);
> > - if (flags & S_CTIME)
> > - fat_truncate_crtime(sbi, now, &inode->i_ctime);
> > - if (flags & S_MTIME)
> > + if (flags & (S_CTIME | S_MTIME)) {
> > fat_truncate_mtime(sbi, now, &inode->i_mtime);
> > + inode->i_ctime = inode->i_mtime;
> > + }
> >
> > return 0;
> > }
>
> --
> OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
