Re: [PATCH V6 4/8] fs/xfs: Make DAX mount option a tri-state

Dave Chinner
2020-04-07T23:59:20Z

On Tue, Apr 07, 2020 at 11:29:54AM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> As agreed upon[1]. We make the dax mount option a tri-state. '-o dax'
> continues to operate the same. We add 'always', 'never', and 'iflag'
> (default).
>
> [1] https://lore.kernel.org/lkml/20200405061945.GA94792@iweiny-DESK2.sc.intel.com/
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes from v5:
> New Patch
> ---
> fs/xfs/xfs_iops.c | 2 +-
> fs/xfs/xfs_mount.h | 26 +++++++++++++++++++++++++-
> fs/xfs/xfs_super.c | 34 +++++++++++++++++++++++++++++-----
> 3 files changed, 55 insertions(+), 7 deletions(-)
>
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 81f2f93caec0..1ec4a36917bd 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1248,7 +1248,7 @@ xfs_inode_supports_dax(
> return false;
>
> /* DAX mount option or DAX iflag must be set. */
> - if (!(mp->m_flags & XFS_MOUNT_DAX) &&
> + if (xfs_mount_dax_mode(mp) != XFS_DAX_ALWAYS &&
> !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> return false;
>
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 88ab09ed29e7..ce027ee06692 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -233,7 +233,31 @@ typedef struct xfs_mount {
> allocator */
> #define XFS_MOUNT_NOATTR2 (1ULL << 25) /* disable use of attr2 format */
>
> -#define XFS_MOUNT_DAX (1ULL << 62) /* TEST ONLY! */
> +/* DAX flag is a 2 bit field representing a tri-state for dax
> + * iflag, always, never
> + * We reserve/document the 2 bits using dax field/field2
> + */
> +#define XFS_DAX_FIELD_MASK 0x3ULL
> +#define XFS_DAX_FIELD_SHIFT 62
> +#define XFS_MOUNT_DAX_FIELD (1ULL << 62)
> +#define XFS_MOUNT_DAX_FIELD2 (1ULL << 63)
> +
> +enum {
> + XFS_DAX_IFLAG = 0,
> + XFS_DAX_ALWAYS = 1,
> + XFS_DAX_NEVER = 2,
> +};
> +
> +static inline void xfs_mount_set_dax(struct xfs_mount *mp, u32 val)
> +{
> + mp->m_flags &= ~(XFS_DAX_FIELD_MASK << XFS_DAX_FIELD_SHIFT);
> + mp->m_flags |= ((val & XFS_DAX_FIELD_MASK) << XFS_DAX_FIELD_SHIFT);
> +}
> +
> +static inline u32 xfs_mount_dax_mode(struct xfs_mount *mp)
> +{
> + return (mp->m_flags >> XFS_DAX_FIELD_SHIFT) & XFS_DAX_FIELD_MASK;
> +}

This is overly complex. Just use 2 flags:

#define XFS_MOUNT_DAX_ALWAYS (1ULL << 26)
#define XFS_MOUNT_DAX_NEVER (1ULL << 27)

and if no mount flag is set, we use the inode flag....

> @@ -59,7 +66,7 @@ enum {
> Opt_filestreams, Opt_quota, Opt_noquota, Opt_usrquota, Opt_grpquota,
> Opt_prjquota, Opt_uquota, Opt_gquota, Opt_pquota,
> Opt_uqnoenforce, Opt_gqnoenforce, Opt_pqnoenforce, Opt_qnoenforce,
> - Opt_discard, Opt_nodiscard, Opt_dax,
> + Opt_discard, Opt_nodiscard, Opt_dax, Opt_dax_enum,
> };
>
> static const struct fs_parameter_spec xfs_fs_parameters[] = {
> @@ -103,6 +110,7 @@ static const struct fs_parameter_spec xfs_fs_parameters[] = {
> fsparam_flag("discard", Opt_discard),
> fsparam_flag("nodiscard", Opt_nodiscard),
> fsparam_flag("dax", Opt_dax),
> + fsparam_enum("dax", Opt_dax_enum, dax_param_enums),
> {}
> };
>
> @@ -129,7 +137,6 @@ xfs_fs_show_options(
> { XFS_MOUNT_GRPID, ",grpid" },
> { XFS_MOUNT_DISCARD, ",discard" },
> { XFS_MOUNT_LARGEIO, ",largeio" },
> - { XFS_MOUNT_DAX, ",dax" },
+ { XFS_MOUNT_DAX_ALWAYS, ",dax=always" },
+ { XFS_MOUNT_DAX_NEVER, ",dax=never" },

> { 0, NULL }
> };
> struct xfs_mount *mp = XFS_M(root->d_sb);
> @@ -185,6 +192,20 @@ xfs_fs_show_options(
> if (!(mp->m_qflags & XFS_ALL_QUOTA_ACCT))
> seq_puts(m, ",noquota");
>
> + switch (xfs_mount_dax_mode(mp)) {
> + case XFS_DAX_IFLAG:
> + seq_puts(m, ",dax=iflag");
> + break;
> + case XFS_DAX_ALWAYS:
> + seq_puts(m, ",dax=always");
> + break;
> + case XFS_DAX_NEVER:
> + seq_puts(m, ",dax=never");
> + break;
> + default:
> + break;
> + }

if (!(mp->m_flags & (XFS_MOUNT_DAX_ALWAYS | XFS_MOUNT_DAX_NEVER))
seq_puts(m, ",dax=iflag");

> +
> return 0;
> }
>
> @@ -1244,7 +1265,10 @@ xfs_fc_parse_param(
> return 0;
> #ifdef CONFIG_FS_DAX
> case Opt_dax:
> - mp->m_flags |= XFS_MOUNT_DAX;
> + xfs_mount_set_dax(mp, XFS_DAX_ALWAYS);
> + return 0;
> + case Opt_dax_enum:
> + xfs_mount_set_dax(mp, result.uint_32);
> return 0;
> #endif
> default:
> @@ -1437,7 +1461,7 @@ xfs_fc_fill_super(
> if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
> sb->s_flags |= SB_I_VERSION;
>
> - if (mp->m_flags & XFS_MOUNT_DAX) {
> + if (xfs_mount_dax_mode(mp) == XFS_DAX_ALWAYS) {

if (mp->m_flags & XFS_MOUNT_DAX_ALWAYS) {

> bool rtdev_is_dax = false, datadev_is_dax;
>
> xfs_warn(mp,
> @@ -1451,7 +1475,7 @@ xfs_fc_fill_super(
> if (!rtdev_is_dax && !datadev_is_dax) {
> xfs_alert(mp,
> "DAX unsupported by block device. Turning off DAX.");
> - mp->m_flags &= ~XFS_MOUNT_DAX;
> + xfs_mount_set_dax(mp, XFS_DAX_NEVER);
> }
> if (xfs_sb_version_hasreflink(&mp->m_sb)) {
> xfs_alert(mp,
> --
> 2.25.1
>
>

--
Dave Chinner
david@fromorbit.com