On Thu, Apr 16, 2020 at 06:57:31PM -0700, Darrick J. Wong wrote: > On Thu, Apr 16, 2020 at 05:37:19PM -0700, Ira Weiny wrote: > > On Thu, Apr 16, 2020 at 03:49:37PM -0700, Darrick J. Wong wrote: > > > On Thu, Apr 16, 2020 at 03:33:27PM -0700, Ira Weiny wrote: > > > > On Thu, Apr 16, 2020 at 09:25:04AM -0700, Darrick J. Wong wrote: > > > > > On Mon, Apr 13, 2020 at 09:00:26PM -0700, ira.weiny@xxxxxxxxx wrote: > > > > > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > > > > > > > > > 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. > > > > > > > > > > > > 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@xxxxxxxxx> > > > > > > --- > > > > > > fs/ext4/ext4.h | 13 +++++++++---- > > > > > > fs/ext4/ioctl.c | 21 ++++++++++++++++++++- > > > > > > 2 files changed, 29 insertions(+), 5 deletions(-) > > > > > > > > > > > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > > > > > > index 61b37a052052..434021fcec88 100644 > > > > > > --- a/fs/ext4/ext4.h > > > > > > +++ b/fs/ext4/ext4.h > > > > > > @@ -415,13 +415,16 @@ struct flex_groups { > > > > > > #define EXT4_VERITY_FL 0x00100000 /* Verity protected inode */ > > > > > > #define EXT4_EA_INODE_FL 0x00200000 /* Inode used for large EA */ > > > > > > #define EXT4_EOFBLOCKS_FL 0x00400000 /* Blocks allocated beyond EOF */ > > > > > > + > > > > > > +#define EXT4_DAX_FL 0x00800000 /* Inode is DAX */ > > > > > > > > > > Sooo, fun fact about ext4 vs. the world-- > > > > > > > > > > The GETFLAGS/SETFLAGS ioctl, since it came from ext2, shares the same > > > > > flag values as the ondisk inode flags in ext*. Therefore, each of these > > > > > EXT4_[whatever]_FL values are supposed to have a FS_[whatever]_FL > > > > > equivalent in include/uapi/linux/fs.h. > > > > > > > > Interesting... > > > > > > > > > > > > > > (Note that the "[whatever]" is a straight translation since the same > > > > > uapi header also defines the FS_XFLAG_[xfswhatever] flag values; ignore > > > > > those.) > > > > > > > > > > Evidently, FS_NOCOW_FL already took 0x800000, but ext4.h was never > > > > > updated to note that the value was taken. I think Ted might be inclined > > > > > to reserve the ondisk inode bit just in case ext4 ever does support copy > > > > > on write, though that's his call. :) > > > > > > > > Seems like I should change this... And I did not realize I was inherently > > > > changing a bit definition which was exposed to other FS's... > > > > > > <nod> This whole thing is a mess, particularly now that we have two vfs > > > ioctls to set per-fs inode attributes, both of which were inherited from > > > other filesystems... :( > > > > > > > Ok I've changed it. > > > > > > > > > > > > > > > Long story short - can you use 0x1000000 for this instead, and add the > > > > > corresponding value to the uapi fs.h? I guess that also means that we > > > > > can change FS_XFLAG_DAX (in the form of FS_DAX_FL in FSSETFLAGS) after > > > > > that. > > > > > > > > :-/ > > > > > > > > Are there any potential users of FS_XFLAG_DAX now? > > > > > > Yes, it's in the userspace ABI so we can't get rid of it. > > > > > > (FWIW there are several flags that exist in both FS_XFLAG_* and FS_*_FL > > > form.) > > > > > > > From what it looks like, changing FS_XFLAG_DAX to FS_DAX_FL would be pretty > > > > straight forward. Just to be sure, looks like XFS converts the FS_[xxx]_FL to > > > > FS_XFLAGS_[xxx] in xfs_merge_ioc_xflags()? But it does not look like all the > > > > FS_[xxx]_FL flags are converted. Is is that XFS does not support those > > > > options? Or is it depending on the VFS layer for some of them? > > > > > > XFS doesn't support most of the FS_*_FL flags. > > > > If FS_XFLAG_DAX needs to continue to be user visible I think we need to keep > > that flag and we should not expose the EXT4_DAX_FL flag... > > > > I think that works for XFS. > > > > But for ext4 it looks like EXT4_FL_XFLAG_VISIBLE was intended to be used for > > [GET|SET]XATTR where EXT4_FL_USER_VISIBLE was intended to for [GET|SET]FLAGS... > > But if I don't add EXT4_DAX_FL in EXT4_FL_XFLAG_VISIBLE my test fails. > > > > I've been playing with the flags and looking at the code and I _thought_ the > > following patch would ensure that FS_XFLAG_DAX is the only one visible but for > > some reason FS_XFLAG_DAX can't be set with this patch. I still need the > > EXT4_FL_USER_VISIBLE mask altered... Which I believe would expose EXT4_DAX_FL > > directly as well. > > > > Jan, Ted? Any ideas? Or should we expose EXT4_DAX_FL and FS_XFLAG_DAX in > > ext4? > > Both flags should be exposed through their respective ioctl interfaces > in both filesystems. That way we don't have to add even more verbiage > to the documentation to instruct userspace programmers on how to special > case ext4 and XFS for the same piece of functionality. Wouldn't it be more confusing for the user to have 2 different flags which do the same thing? I would think that using FS_XFLAG_DAX _only_ (for both ext4 and xfs) would be easier without special cases? Ira