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

Darrick J. Wong
2020-04-16T16:27:35Z

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.

(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. :)

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.

--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
>