vfs: add hooks for ext4's delayed allocation support

From: Alex Tomas <alex@clusterfs.com>

Export mpage_bio_submit() and __mpage_writepage() for the benefit of
ext4's delayed allocation support.   Also change __block_write_full_page
so that if buffers that have the BH_Delay flag set it will call
get_block() to get the physical block allocated, just as in the
!BH_Mapped case.

Signed-off-by: Alex Tomas <alex@clusterfs.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

---
 fs/buffer.c           |    7 +++++--
 fs/mpage.c            |   14 +++++---------
 include/linux/mpage.h |   10 ++++++++++
 3 files changed, 20 insertions(+), 11 deletions(-)

Index: linux-2.6.26-rc9/fs/buffer.c
===================================================================
--- linux-2.6.26-rc9.orig/fs/buffer.c	2008-07-11 16:05:08.000000000 -0700
+++ linux-2.6.26-rc9/fs/buffer.c	2008-07-11 16:05:11.000000000 -0700
@@ -1691,11 +1691,13 @@ static int __block_write_full_page(struc
 			 */
 			clear_buffer_dirty(bh);
 			set_buffer_uptodate(bh);
-		} else if (!buffer_mapped(bh) && buffer_dirty(bh)) {
+		} else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
+			   buffer_dirty(bh)) {
 			WARN_ON(bh->b_size != blocksize);
 			err = get_block(inode, block, bh, 1);
 			if (err)
 				goto recover;
+			clear_buffer_delay(bh);
 			if (buffer_new(bh)) {
 				/* blockdev mappings never come here */
 				clear_buffer_new(bh);
@@ -1774,7 +1776,8 @@ recover:
 	bh = head;
 	/* Recovery: lock and submit the mapped buffers */
 	do {
-		if (buffer_mapped(bh) && buffer_dirty(bh)) {
+		if (buffer_mapped(bh) && buffer_dirty(bh) &&
+		    !buffer_delay(bh)) {
 			lock_buffer(bh);
 			mark_buffer_async_write(bh);
 		} else {
Index: linux-2.6.26-rc9/fs/mpage.c
===================================================================
--- linux-2.6.26-rc9.orig/fs/mpage.c	2008-07-11 16:04:27.000000000 -0700
+++ linux-2.6.26-rc9/fs/mpage.c	2008-07-11 16:05:11.000000000 -0700
@@ -82,7 +82,7 @@ static void mpage_end_io_write(struct bi
 	bio_put(bio);
 }
 
-static struct bio *mpage_bio_submit(int rw, struct bio *bio)
+struct bio *mpage_bio_submit(int rw, struct bio *bio)
 {
 	bio->bi_end_io = mpage_end_io_read;
 	if (rw == WRITE)
@@ -90,6 +90,7 @@ static struct bio *mpage_bio_submit(int 
 	submit_bio(rw, bio);
 	return NULL;
 }
+EXPORT_SYMBOL(mpage_bio_submit);
 
 static struct bio *
 mpage_alloc(struct block_device *bdev,
@@ -435,15 +436,9 @@ EXPORT_SYMBOL(mpage_readpage);
  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
  * just allocate full-size (16-page) BIOs.
  */
-struct mpage_data {
-	struct bio *bio;
-	sector_t last_block_in_bio;
-	get_block_t *get_block;
-	unsigned use_writepage;
-};
 
-static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
-			     void *data)
+int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+		      void *data)
 {
 	struct mpage_data *mpd = data;
 	struct bio *bio = mpd->bio;
@@ -651,6 +646,7 @@ out:
 	mpd->bio = bio;
 	return ret;
 }
+EXPORT_SYMBOL(__mpage_writepage);
 
 /**
  * mpage_writepages - walk the list of dirty pages of the given address space & writepage() all of them
Index: linux-2.6.26-rc9/include/linux/mpage.h
===================================================================
--- linux-2.6.26-rc9.orig/include/linux/mpage.h	2008-07-11 16:04:27.000000000 -0700
+++ linux-2.6.26-rc9/include/linux/mpage.h	2008-07-11 16:05:11.000000000 -0700
@@ -11,11 +11,21 @@
  */
 #ifdef CONFIG_BLOCK
 
+struct mpage_data {
+	struct bio *bio;
+	sector_t last_block_in_bio;
+	get_block_t *get_block;
+	unsigned use_writepage;
+};
+
 struct writeback_control;
 
+struct bio *mpage_bio_submit(int rw, struct bio *bio);
 int mpage_readpages(struct address_space *mapping, struct list_head *pages,
 				unsigned nr_pages, get_block_t get_block);
 int mpage_readpage(struct page *page, get_block_t get_block);
+int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+		      void *data);
 int mpage_writepages(struct address_space *mapping,
 		struct writeback_control *wbc, get_block_t get_block);
 int mpage_writepage(struct page *page, get_block_t *get_block,