Re: [PATCH V4 1/8] fs/ext4: Narrow scope of DAX check in setflags

Jan Kara
2020-05-22T07:58:23Z

On Thu 21-05-20 12:13:06, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> When preventing DAX and journaling on an inode. Use the effective DAX
> check rather than the mount option.
>
> This will be required to support per inode DAX flags.
>
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
...
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index bfc1281fc4cb..5813e5e73eab 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -393,9 +393,9 @@ static int ext4_ioctl_setflags(struct inode *inode,
> if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL)) {
> /*
> * Changes to the journaling mode can cause unsafe changes to
> - * S_DAX if we are using the DAX mount option.
> + * S_DAX if the inode is DAX
> */
> - if (test_opt(inode->i_sb, DAX)) {
> + if (IS_DAX(inode)) {
> err = -EBUSY;
> goto flags_out;
> }

Now one problem popped up in my mind: We should also make EXT4_JOURNAL_DATA_FL
and EXT4_DAX_FL exclusive so that both cannot be turned on at the same
time. And IS_DAX() check isn't enough for that. Sorry for not noticing
earlier... it's like peeling an onion...

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR