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    SubjectRe: [PATCH V6 4/8] fs/xfs: Make DAX mount option a tri-state
    On Wed, Apr 08, 2020 at 09:59:09AM +1000, Dave Chinner wrote:
    > 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:

    LOL... I was afraid someone would say that. At first I used 2 flags with
    fsparam_string, but then I realized Darrick suggested fsparam_enum:

    "It would be handy if we could have a single fsparam_enum for figuring
    out the dax mount options."

    -- https://lore.kernel.org/lkml/20200403183746.GQ80283@magnolia/

    So I changed it...

    Darrick?

    Ira

    >
    > #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

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