[PATCH 10/15] xfs: kill xfs_dmcore_stub

[Alex Elder <aelder@xxxxxxx>]

Nobody ever dereferences an XFS mount point's m_dm_ops vector
pointer any more unless the XFS_MOUNT_DMAPI mount flag is set.  So
leverage that to just use a null pointer there in that case, and
drop the whole xfs_dmcore_stub variable.

Change it so that once the m_dm_ops vector has had a chance to be
assigned at mount time, a non-null m_vm_ops pointer is always used
to indicate DMAPI is active on a file system rather than looking at
the mount flag.

Also rearrange the logic in xfs_dmops_get() a bit to avoid
including much of the code in the case DMAPI isn't supported
at build time.

Signed-off-by: Alex Elder <aelder@xxxxxxx>

---
 fs/xfs/linux-2.6/xfs_file.c |    6 ++----
 fs/xfs/xfs_dmapi.h          |   10 +++++-----
 fs/xfs/xfs_dmops.c          |   37 +++++++++++++++++++++----------------
 3 files changed, 28 insertions(+), 25 deletions(-)

Index: b/fs/xfs/linux-2.6/xfs_file.c
===================================================================
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -674,8 +674,7 @@ start:
                goto out_unlock_mutex;
        }
 
-       if (mp->m_flags & XFS_MOUNT_DMAPI && !(ioflags & IO_INVIS) &&
-                       !eventsent) {
+       if (mp->m_dm_ops && !(ioflags & IO_INVIS) && !eventsent) {
                int     dmflags = FILP_DELAY_FLAG(file);
 
                if (need_i_mutex)
@@ -830,8 +829,7 @@ write_retry:
                xfs_iunlock(ip, XFS_ILOCK_EXCL);
        }
 
-       if (ret == -ENOSPC && mp->m_flags & XFS_MOUNT_DMAPI &&
-                       !(ioflags & IO_INVIS)) {
+       if (ret == -ENOSPC && mp->m_dm_ops && !(ioflags & IO_INVIS)) {
                xfs_iunlock(ip, iolock);
                if (need_i_mutex)
                        mutex_unlock(&inode->i_mutex);
Index: b/fs/xfs/xfs_dmapi.h
===================================================================
--- a/fs/xfs/xfs_dmapi.h
+++ b/fs/xfs/xfs_dmapi.h
@@ -201,7 +201,7 @@ xfs_dmapi_event_enabled(struct xfs_inode
 #ifdef XFS_DMAPI
        unsigned int event_mask = 1 << event;
 
-       return ip->i_mount->m_flags & XFS_MOUNT_DMAPI &&
+       return ip->i_mount->m_dm_ops &&
                (ip->i_mount->m_dmevmask & event_mask ||
                        ip->i_d.di_dmevmask & event_mask);
 #else /* ! XFS_DMAPI */
@@ -235,7 +235,7 @@ xfs_dmapi_send_mmap(
        struct inode            *inode = vma->vm_file->f_path.dentry->d_inode;
        struct xfs_mount        *mp = XFS_M(inode->i_sb);
 
-       if (mp->m_flags & XFS_MOUNT_DMAPI) {
+       if (mp->m_dm_ops) {
                xfs_send_mmap_t send_mmap = mp->m_dm_ops->xfs_send_mmap;
 
                return send_mmap(vma, vm_flags);
@@ -319,7 +319,7 @@ xfs_dmapi_send_mount(
        struct xfs_mount        *mp,
        char                    *path)
 {
-       if (mp->m_flags & XFS_MOUNT_DMAPI) {
+       if (mp->m_dm_ops) {
                xfs_send_mount_t send_mount = mp->m_dm_ops->xfs_send_mount;
 
                return send_mount(mp, DM_RIGHT_NULL, path, mp->m_fsname);
@@ -333,7 +333,7 @@ static inline void
 xfs_dmapi_send_preunmount(
        struct xfs_mount        *mp)
 {
-       if (mp->m_flags & XFS_MOUNT_DMAPI)
+       if (mp->m_dm_ops)
                (void) xfs_dmapi_send_namesp(mp->m_rootip, DM_RIGHT_NULL, NULL,
                                        DM_EVENT_PREUNMOUNT,
                                        mp->m_rootip, DM_RIGHT_NULL, NULL,
@@ -344,7 +344,7 @@ static inline void
 xfs_dmapi_send_unmount(
        struct xfs_mount        *mp)
 {
-       if (mp->m_flags & XFS_MOUNT_DMAPI) {
+       if (mp->m_dm_ops) {
                xfs_send_unmount_t send_unmount =
                                        mp->m_dm_ops->xfs_send_unmount;
 
Index: b/fs/xfs/xfs_dmops.c
===================================================================
--- a/fs/xfs/xfs_dmops.c
+++ b/fs/xfs/xfs_dmops.c
@@ -28,30 +28,35 @@
 #include "xfs_inode.h"
 #include "xfs_dmapi.h"
 
-
-static struct xfs_dmops xfs_dmcore_stub = {
-       .xfs_send_data          = (xfs_send_data_t)fs_nosys,
-       .xfs_send_mmap          = (xfs_send_mmap_t)fs_noerr,
-       .xfs_send_destroy       = (xfs_send_destroy_t)fs_nosys,
-       .xfs_send_namesp        = (xfs_send_namesp_t)fs_nosys,
-       .xfs_send_mount         = (xfs_send_mount_t)fs_nosys,
-       .xfs_send_unmount       = (xfs_send_unmount_t)fs_noerr,
-};
-
 int
 xfs_dmops_get(struct xfs_mount *mp)
 {
-       if (mp->m_flags & XFS_MOUNT_DMAPI) {
-               cmn_err(CE_WARN,
-                       "XFS: dmapi support not available in this kernel.");
-               return EINVAL;
+       ASSERT(!mp->m_dm_ops);
+       if (!(mp->m_flags & XFS_MOUNT_DMAPI))
+               return 0;
+
+#ifdef XFS_DMAPI
+       mp->m_dm_ops = symbol_get(xfs_dmcore_xfs);
+       if (!mp->m_dm_ops) {
+               request_module("xfs_dmapi");
+               mp->m_dm_ops = symbol_get(xfs_dmcore_xfs);
        }
+       if (mp->m_dm_ops)
+               return 0;
+#endif /* XFS_DMAPI */
 
-       mp->m_dm_ops = &xfs_dmcore_stub;
-       return 0;
+       /* Turn off the flag, since it won't be operative */
+       mp->m_flags &= ~XFS_MOUNT_DMAPI;
+       cmn_err(CE_WARN, "XFS: dmapi support not available in this kernel.");
+
+       return EINVAL;
 }
 
 void
 xfs_dmops_put(struct xfs_mount *mp)
 {
+       if (mp->m_dm_ops) {
+               symbol_put(xfs_dmcore_xfs);
+               mp->m_dm_ops = NULL;
+       }
 }