[XFS] Initial pass at going directly-to-bio on the buffered IO path. This

allows us to submit much larger I/Os instead of sending down lots of small
buffer_heads.  To do this we need to have a rather complicated I/O
submission and completion tracking infrastructure.  Part of the latter has
been merged already a long time ago for direct I/O support. Part of the
problem is that we need to track sub-pagesize regions and for that we
still need buffer_heads for the time beeing.  Long-term I hope we can move
to better data strucutures and/or maybe move this to fs/mpage.c instead of
having it in XFS.  Original patch from Nathan Scott with various updates
from David Chinner and Christoph Hellwig.

SGI-PV: 947118
SGI-Modid: xfs-linux-melb:xfs-kern:203822a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>

fs/xfs/linux-2.6/xfs_aops.h

@@ -23,14 +23,24 @@ extern mempool_t *xfs_ioend_pool;
 
 typedef void (*xfs_ioend_func_t)(void *);
 
+/*
+ * xfs_ioend struct manages large extent writes for XFS.
+ * It can manage several multi-page bio's at once.
+ */
 typedef struct xfs_ioend {
+	struct xfs_ioend	*io_list;	/* next ioend in chain */
+	unsigned int		io_type;	/* delalloc / unwritten */
 	unsigned int		io_uptodate;	/* I/O status register */
 	atomic_t		io_remaining;	/* hold count */
 	struct vnode		*io_vnode;	/* file being written to */
 	struct buffer_head	*io_buffer_head;/* buffer linked list head */
+	struct buffer_head	*io_buffer_tail;/* buffer linked list tail */
 	size_t			io_size;	/* size of the extent */
 	xfs_off_t		io_offset;	/* offset in the file */
 	struct work_struct	io_work;	/* xfsdatad work queue */
 } xfs_ioend_t;
 
+extern struct address_space_operations linvfs_aops;
+extern int linvfs_get_block(struct inode *, sector_t, struct buffer_head *, int);
+
 #endif /* __XFS_IOPS_H__ */

fs/xfs/linux-2.6/xfs_iops.h

@@ -26,11 +26,6 @@ extern struct file_operations linvfs_file_operations;
 extern struct file_operations linvfs_invis_file_operations;
 extern struct file_operations linvfs_dir_operations;
 
-extern struct address_space_operations linvfs_aops;
-
-extern int linvfs_get_block(struct inode *, sector_t, struct buffer_head *, int);
-extern void linvfs_unwritten_done(struct buffer_head *, int);
-
 extern int xfs_ioctl(struct bhv_desc *, struct inode *, struct file *,
                         int, unsigned int, void __user *);
 

fs/xfs/linux-2.6/xfs_linux.h

@@ -110,10 +110,6 @@
  * delalloc and these ondisk-uninitialised buffers.
  */
 BUFFER_FNS(PrivateStart, unwritten);
-static inline void set_buffer_unwritten_io(struct buffer_head *bh)
-{
-	bh->b_end_io = linvfs_unwritten_done;
-}
 
 #define restricted_chown	xfs_params.restrict_chown.val
 #define irix_sgid_inherit	xfs_params.sgid_inherit.val