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[PATCH 6/6] xfs: add initial DAX support

To: xfs@xxxxxxxxxxx
Subject: [PATCH 6/6] xfs: add initial DAX support
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 4 Mar 2015 10:30:27 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, jack@xxxxxxx, willy@xxxxxxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1425425427-16283-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1425425427-16283-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

Add initial DAX support to XFS. To do this we need a new mount
option to turn DAX on filesystem, and we need to propagate thi into
the inode flags whenever an inode is instantiated so that the
per-inode checks throughout the code Do The Right Thing.

There are still some things remaining to be done:

        - needs per-inode flags to mark inodes as DAX enabled, and
          an inheritance flag to enable automatic filesystem
          propagation of the property
        - fails occasionally with zero length writes instead of
          ENOSPC errors, so error propagation inside/from the DAX
          code need work
        - occasionally creates two extents rather than a single
          larger extent like non-dax filesystems.
        - much more testing

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_iops.c  | 24 ++++++++++++------------
 fs/xfs/xfs_mount.h |  2 ++
 fs/xfs/xfs_super.c | 25 +++++++++++++++++++++++--
 3 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 3ff24c3..887d196 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1195,22 +1195,22 @@ xfs_diflags_to_iflags(
        struct inode            *inode,
        struct xfs_inode        *ip)
 {
-       if (ip->i_d.di_flags & XFS_DIFLAG_IMMUTABLE)
+       uint16_t                flags = ip->i_d.di_flags;
+
+       inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC |
+                           S_NOATIME | S_DAX);
+
+       if (flags & XFS_DIFLAG_IMMUTABLE)
                inode->i_flags |= S_IMMUTABLE;
-       else
-               inode->i_flags &= ~S_IMMUTABLE;
-       if (ip->i_d.di_flags & XFS_DIFLAG_APPEND)
+       if (flags & XFS_DIFLAG_APPEND)
                inode->i_flags |= S_APPEND;
-       else
-               inode->i_flags &= ~S_APPEND;
-       if (ip->i_d.di_flags & XFS_DIFLAG_SYNC)
+       if (flags & XFS_DIFLAG_SYNC)
                inode->i_flags |= S_SYNC;
-       else
-               inode->i_flags &= ~S_SYNC;
-       if (ip->i_d.di_flags & XFS_DIFLAG_NOATIME)
+       if (flags & XFS_DIFLAG_NOATIME)
                inode->i_flags |= S_NOATIME;
-       else
-               inode->i_flags &= ~S_NOATIME;
+       /* XXX: Also needs an on-disk per inode flag! */
+       if (ip->i_mount->m_flags & XFS_MOUNT_DAX)
+               inode->i_flags |= S_DAX;
 }
 
 /*
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 8c995a2..cd44e88 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -179,6 +179,8 @@ typedef struct xfs_mount {
                                                   allocator */
 #define XFS_MOUNT_NOATTR2      (1ULL << 25)    /* disable use of attr2 format 
*/
 
+#define XFS_MOUNT_DAX          (1ULL << 62)    /* TEST ONLY! */
+
 
 /*
  * Default minimum read and write sizes.
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 3ad0b17..0f26d7a 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -112,6 +112,8 @@ static struct xfs_kobj xfs_dbg_kobj;        /* global debug 
sysfs attrs */
 #define MNTOPT_DISCARD    "discard"    /* Discard unused blocks */
 #define MNTOPT_NODISCARD   "nodiscard" /* Do not discard unused blocks */
 
+#define MNTOPT_DAX     "dax"           /* Enable direct access to bdev pages */
+
 /*
  * Table driven mount option parser.
  *
@@ -363,6 +365,10 @@ xfs_parseargs(
                        mp->m_flags |= XFS_MOUNT_DISCARD;
                } else if (!strcmp(this_char, MNTOPT_NODISCARD)) {
                        mp->m_flags &= ~XFS_MOUNT_DISCARD;
+#ifdef CONFIG_FS_DAX
+               } else if (!strcmp(this_char, MNTOPT_DAX)) {
+                       mp->m_flags |= XFS_MOUNT_DAX;
+#endif
                } else {
                        xfs_warn(mp, "unknown mount option [%s].", this_char);
                        return -EINVAL;
@@ -452,8 +458,8 @@ done:
 }
 
 struct proc_xfs_info {
-       int     flag;
-       char    *str;
+       uint64_t        flag;
+       char            *str;
 };
 
 STATIC int
@@ -474,6 +480,7 @@ xfs_showargs(
                { XFS_MOUNT_GRPID,              "," MNTOPT_GRPID },
                { XFS_MOUNT_DISCARD,            "," MNTOPT_DISCARD },
                { XFS_MOUNT_SMALL_INUMS,        "," MNTOPT_32BITINODE },
+               { XFS_MOUNT_DAX,                "," MNTOPT_DAX },
                { 0, NULL }
        };
        static struct proc_xfs_info xfs_info_unset[] = {
@@ -1501,6 +1508,20 @@ xfs_fs_fill_super(
        if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
                sb->s_flags |= MS_I_VERSION;
 
+       if (mp->m_flags & XFS_MOUNT_DAX) {
+               xfs_warn(mp,
+       "DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
+               if (sb->s_blocksize != PAGE_SIZE) {
+                       xfs_alert(mp,
+               "Filesystem block size invalid for DAX Turning DAX off.");
+                       mp->m_flags &= ~XFS_MOUNT_DAX;
+               } else if (!sb->s_bdev->bd_disk->fops->direct_access) {
+                       xfs_alert(mp,
+               "Block device does not support DAX Turning DAX off.");
+                       mp->m_flags &= ~XFS_MOUNT_DAX;
+               }
+       }
+
        error = xfs_mountfs(mp);
        if (error)
                goto out_filestream_unmount;
-- 
2.0.0

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