block: Add support for DAX reads/writes to block devices

If a block device supports the ->direct_access methods, bypass the normal
DIO path and use DAX to go straight to memcpy() instead of allocating
a DIO and a BIO.

Includes support for the DIO_SKIP_DIO_COUNT flag in DAX, as is done in
do_blockdev_direct_IO().

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 159f796afa85..37a0c4826c1a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -209,7 +209,8 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
         }
 
         /* Protects against truncate */
-        inode_dio_begin(inode);
+        if (!(flags & DIO_SKIP_DIO_COUNT))
+                inode_dio_begin(inode);
 
         retval = dax_io(inode, iter, pos, end, get_block, &bh);
 
@@ -219,7 +220,8 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
         if ((retval > 0) && end_io)
                 end_io(iocb, pos, retval, bh.b_private);
 
-        inode_dio_end(inode);
+        if (!(flags & DIO_SKIP_DIO_COUNT))
+                inode_dio_end(inode);
  out:
         return retval;
 }