Re: [PATCH V4 7/8] fs/ext4: Introduce DAX inode flag

Ira Weiny
2020-05-25T04:39:13Z

On Fri, May 22, 2020 at 01:48:48PM +0200, Jan Kara wrote:
> On Thu 21-05-20 12:13:12, ira.weiny@intel.com wrote:
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > Add a flag to preserve FS_XFLAG_DAX in the ext4 inode.
> >
> > Set the flag to be user visible and changeable. Set the flag to be
> > inherited. Allow applications to change the flag at any time with the
> > exception of if VERITY or ENCRYPT is set.
> >
> > Disallow setting VERITY or ENCRYPT if DAX is set.
> >
> > Finally, on regular files, flag the inode to not be cached to facilitate
> > changing S_DAX on the next creation of the inode.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ...
>
> > @@ -303,6 +318,16 @@ static int ext4_ioctl_setflags(struct inode *inode,
> > unsigned int jflag;
> > struct super_block *sb = inode->i_sb;
> >
> > + if (ext4_test_inode_flag(inode, EXT4_INODE_DAX)) {
> > + if (ext4_test_inode_flag(inode, EXT4_INODE_VERITY) ||
> > + ext4_test_inode_flag(inode, EXT4_INODE_ENCRYPT) ||
> > + ext4_test_inode_state(inode,
> > + EXT4_STATE_VERITY_IN_PROGRESS)) {
> > + err = -EOPNOTSUPP;
> > + goto flags_out;
> > + }
> > + }
>
> The way this check is implemented wouldn't IMO do what we need... It
> doesn't check the flags that are being set but just the current inode
> state. I think it should rather be:

Sorry, I got confused by the flags when I wrote this.

>
> if ((flags ^ oldflags) & EXT4_INODE_DAX_FL) {
> ...
> }
>
> And perhaps move this to a place in ext4_ioctl_setflags() where we check
> other similar conflicts.

Sure. It seems like a ext4_setflags_prepare() helper would be in order. I'll
see what I can do.

>
> And then we should check conflicts with the journal flag as well, as I
> mentioned in reply to the first patch. There it is more complicated by the
> fact that we should disallow setting of both EXT4_INODE_DAX_FL and
> EXT4_JOURNAL_DATA_FL at the same time so the checks will be somewhat more
> complicated.

I'm confused by jflag. Why is EXT4_JOURNAL_DATA_FL stored in jflag?

Ira

>
> Honza
>
> > +
> > /* Is it quota file? Do not allow user to mess with it */
> > if (ext4_is_quota_file(inode))
> > goto flags_out;
> --
> Jan Kara <jack@suse.com>
> SUSE Labs, CR