Re: [PATCH 8/9] fs/ext4: Introduce DAX inode flag

Jan Kara
2020-05-13T15:05:11Z

On Tue 12-05-20 22:43:23, 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>
>
> ---
> Change from RFC:
> use new d_mark_dontcache()
> Allow caching if ALWAYS/NEVER is set
> Rebased to latest Linus master
> Change flag to unused 0x01000000
> update ext4_should_enable_dax()
> ---
> fs/ext4/ext4.h | 13 +++++++++----
> fs/ext4/inode.c | 4 +++-
> fs/ext4/ioctl.c | 25 ++++++++++++++++++++++++-
> 3 files changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 01d1de838896..715f8f2029b2 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 */
> /* 0x00400000 was formerly EXT4_EOFBLOCKS_FL */
> +
> +#define EXT4_DAX_FL 0x01000000 /* Inode is DAX */
> +
> #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 0x715BDFFF /* User visible flags */
> +#define EXT4_FL_USER_MODIFIABLE 0x614BC0FF /* User modifiable flags */

Hum, I think this was already mentioned but there are also definitions in
include/uapi/linux/fs.h which should be kept in sync... Also if DAX flag
gets modified through FS_IOC_SETFLAGS, we should call ext4_doncache() as
well, shouldn't we?

> @@ -802,6 +807,21 @@ 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 (test_opt2(inode->i_sb, DAX_NEVER) ||
> + test_opt(inode->i_sb, DAX_ALWAYS))
> + return;
> +
> + if (((ei->i_flags ^ flags) & EXT4_DAX_FL) == EXT4_DAX_FL)
> + d_mark_dontcache(inode);
> +}
> +
> long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> struct inode *inode = file_inode(filp);
> @@ -1267,6 +1287,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return err;
>
> inode_lock(inode);
> +
> + ext4_dax_dontcache(inode, flags);
> +

I don't think we should set dontcache flag when setting of DAX flag fails -
it could event be a security issue). So I think you'll have to check
whether DAX flag is being changed, call vfs_ioc_fssetxattr_check(), and
only if it succeeded and DAX flags was changing call ext4_dax_dontcache().

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