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

[Darrick J. Wong]

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.

(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
>