Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag

Darrick J. Wong
2020-04-16T22:50:03Z

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@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.
> > >
> > > 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>
> > > ---
> > > 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... :(

> >
> > 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.

--D

> Ira
>
> >
> > --D
> >
> > > +
> > > #define EXT4_INLINE_DATA_FL 0x10000000 /* Inode has inline data. */
> > > #define EXT4_PROJINHERIT_FL 0x20000000 /* Create with parents projid */
> > > #define EXT4_CASEFOLD_FL 0x40000000 /* Casefolded file */
> > > #define EXT4_RESERVED_FL 0x80000000 /* reserved for ext4 lib */
> > >
> > > -#define EXT4_FL_USER_VISIBLE 0x705BDFFF /* User visible flags */
> > > -#define EXT4_FL_USER_MODIFIABLE 0x604BC0FF /* User modifiable flags */
> > > +#define EXT4_FL_USER_VISIBLE 0x70DBDFFF /* User visible flags */
> > > +#define EXT4_FL_USER_MODIFIABLE 0x60CBC0FF /* User modifiable flags */
> > >
> > > /* Flags we can manipulate with through EXT4_IOC_FSSETXATTR */
> > > #define EXT4_FL_XFLAG_VISIBLE (EXT4_SYNC_FL | \
> > > @@ -429,14 +432,16 @@ struct flex_groups {
> > > EXT4_APPEND_FL | \
> > > EXT4_NODUMP_FL | \
> > > EXT4_NOATIME_FL | \
> > > - EXT4_PROJINHERIT_FL)
> > > + EXT4_PROJINHERIT_FL | \
> > > + EXT4_DAX_FL)
> > >
> > > /* Flags that should be inherited by new inodes from their parent. */
> > > #define EXT4_FL_INHERITED (EXT4_SECRM_FL | EXT4_UNRM_FL | EXT4_COMPR_FL |\
> > > EXT4_SYNC_FL | EXT4_NODUMP_FL | EXT4_NOATIME_FL |\
> > > EXT4_NOCOMPR_FL | EXT4_JOURNAL_DATA_FL |\
> > > EXT4_NOTAIL_FL | EXT4_DIRSYNC_FL |\
> > > - EXT4_PROJINHERIT_FL | EXT4_CASEFOLD_FL)
> > > + EXT4_PROJINHERIT_FL | EXT4_CASEFOLD_FL |\
> > > + EXT4_DAX_FL)
> > >
> > > /* Flags that are appropriate for regular files (all but dir-specific ones). */
> > > #define EXT4_REG_FLMASK (~(EXT4_DIRSYNC_FL | EXT4_TOPDIR_FL | EXT4_CASEFOLD_FL |\
> > > diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> > > index ee3401a32e79..ca07d5086f03 100644
> > > --- a/fs/ext4/ioctl.c
> > > +++ b/fs/ext4/ioctl.c
> > > @@ -539,12 +539,15 @@ static inline __u32 ext4_iflags_to_xflags(unsigned long iflags)
> > > xflags |= FS_XFLAG_NOATIME;
> > > if (iflags & EXT4_PROJINHERIT_FL)
> > > xflags |= FS_XFLAG_PROJINHERIT;
> > > + if (iflags & EXT4_DAX_FL)
> > > + xflags |= FS_XFLAG_DAX;
> > > return xflags;
> > > }
> > >
> > > #define EXT4_SUPPORTED_FS_XFLAGS (FS_XFLAG_SYNC | FS_XFLAG_IMMUTABLE | \
> > > FS_XFLAG_APPEND | FS_XFLAG_NODUMP | \
> > > - FS_XFLAG_NOATIME | FS_XFLAG_PROJINHERIT)
> > > + FS_XFLAG_NOATIME | FS_XFLAG_PROJINHERIT | \
> > > + FS_XFLAG_DAX)
> > >
> > > /* Transfer xflags flags to internal */
> > > static inline unsigned long ext4_xflags_to_iflags(__u32 xflags)
> > > @@ -563,6 +566,8 @@ static inline unsigned long ext4_xflags_to_iflags(__u32 xflags)
> > > iflags |= EXT4_NOATIME_FL;
> > > if (xflags & FS_XFLAG_PROJINHERIT)
> > > iflags |= EXT4_PROJINHERIT_FL;
> > > + if (xflags & FS_XFLAG_DAX)
> > > + iflags |= EXT4_DAX_FL;
> > >
> > > return iflags;
> > > }
> > > @@ -813,6 +818,17 @@ static int ext4_ioctl_get_es_cache(struct file *filp, unsigned long arg)
> > > return error;
> > > }
> > >
> > > +static void ext4_dax_dontcache(struct inode *inode, unsigned int flags)
> > > +{
> > > + struct ext4_inode_info *ei = EXT4_I(inode);
> > > +
> > > + if (S_ISDIR(inode->i_mode))
> > > + return;
> > > +
> > > + if ((ei->i_flags ^ flags) == EXT4_DAX_FL)
> > > + inode->i_state |= I_DONTCACHE;
> > > +}
> > > +
> > > long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > > {
> > > struct inode *inode = file_inode(filp);
> > > @@ -1273,6 +1289,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > > return err;
> > >
> > > inode_lock(inode);
> > > +
> > > + ext4_dax_dontcache(inode, flags);
> > > +
> > > ext4_fill_fsxattr(inode, &old_fa);
> > > err = vfs_ioc_fssetxattr_check(inode, &old_fa, &fa);
> > > if (err)
> > > --
> > > 2.25.1
> > >