btrfs: Remove extent_io_ops::writepage_start_hook

This hook is called only from __extent_writepage_io which is already
called only from the data page writeout path. So there is no need to
make an indirect call via extent_io_ops. This patch just removes the
callback definition, exports the callback function and calls it directly
at the only call site. Also give the function a more descriptive name.
No functional changes.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3192,6 +3192,7 @@ int btrfs_prealloc_file_range_trans(struct inode *inode,
 int btrfs_run_delalloc_range(void *private_data, struct page *locked_page,
 		u64 start, u64 end, int *page_started, unsigned long *nr_written,
 		struct writeback_control *wbc);
+int btrfs_writepage_cow_fixup(struct page *page, u64 start, u64 end);
 extern const struct dentry_operations btrfs_dentry_operations;
 
 /* ioctl.c */

fs/btrfs/extent_io.c

@@ -3321,20 +3321,17 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 	int nr = 0;
 	bool compressed;
 
-	if (tree->ops && tree->ops->writepage_start_hook) {
-		ret = tree->ops->writepage_start_hook(page, start,
-						      page_end);
-		if (ret) {
-			/* Fixup worker will requeue */
-			if (ret == -EBUSY)
-				wbc->pages_skipped++;
-			else
-				redirty_page_for_writepage(wbc, page);
+	ret = btrfs_writepage_cow_fixup(page, start, page_end);
+	if (ret) {
+		/* Fixup worker will requeue */
+		if (ret == -EBUSY)
+			wbc->pages_skipped++;
+		else
+			redirty_page_for_writepage(wbc, page);
 
-			update_nr_written(wbc, nr_written);
-			unlock_page(page);
-			return 1;
-		}
+		update_nr_written(wbc, nr_written);
+		unlock_page(page);
+		return 1;
 	}
 
 	/*

fs/btrfs/extent_io.h

@@ -106,7 +106,6 @@ struct extent_io_ops {
 	/*
 	 * Optional hooks, called if the pointer is not NULL
 	 */
-	int (*writepage_start_hook)(struct page *page, u64 start, u64 end);
 	void (*writepage_end_io_hook)(struct page *page, u64 start, u64 end,
 				      struct extent_state *state, int uptodate);
 	void (*set_bit_hook)(void *private_data, struct extent_state *state,

fs/btrfs/inode.c

@@ -2152,7 +2152,7 @@ out_page:
  * to fix it up.  The async helper will wait for ordered extents, set
  * the delalloc bit and make it safe to write the page.
  */
-static int btrfs_writepage_start_hook(struct page *page, u64 start, u64 end)
+int btrfs_writepage_cow_fixup(struct page *page, u64 start, u64 end)
 {
 	struct inode *inode = page->mapping->host;
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
@@ -10527,7 +10527,6 @@ static const struct extent_io_ops btrfs_extent_io_ops = {
 
 	/* optional callbacks */
 	.writepage_end_io_hook = btrfs_writepage_end_io_hook,
-	.writepage_start_hook = btrfs_writepage_start_hook,
 	.set_bit_hook = btrfs_set_bit_hook,
 	.clear_bit_hook = btrfs_clear_bit_hook,
 	.merge_extent_hook = btrfs_merge_extent_hook,