btrfs: Refactor btrfs_merge_bio_hook

This function really checks whether adding more data to the bio will
straddle a stripe/chunk. So first let's give it a more appropraite name
- btrfs_bio_fits_in_stripe. Secondly, the offset parameter was never
used to just remove it. Thirdly, pages are submitted to either btree or
data inodes so it's guaranteed that tree->ops is set so replace the
check with an ASSERT. Finally, document the parameters of the function.
No functional changes.

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/compression.c

@@ -332,7 +332,8 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
 		page = compressed_pages[pg_index];
 		page->mapping = inode->i_mapping;
 		if (bio->bi_iter.bi_size)
-			submit = btrfs_merge_bio_hook(page, 0, PAGE_SIZE, bio, 0);
+			submit = btrfs_bio_fits_in_stripe(page, PAGE_SIZE, bio,
+							  0);
 
 		page->mapping = NULL;
 		if (submit || bio_add_page(bio, page, PAGE_SIZE, 0) <
@@ -610,8 +611,8 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		page->index = em_start >> PAGE_SHIFT;
 
 		if (comp_bio->bi_iter.bi_size)
-			submit = btrfs_merge_bio_hook(page, 0, PAGE_SIZE,
-					comp_bio, 0);
+			submit = btrfs_bio_fits_in_stripe(page, PAGE_SIZE,
+							  comp_bio, 0);
 
 		page->mapping = NULL;
 		if (submit || bio_add_page(comp_bio, page, PAGE_SIZE, 0) <

fs/btrfs/ctree.h

@@ -3191,9 +3191,8 @@ void btrfs_merge_delalloc_extent(struct inode *inode, struct extent_state *new,
 				 struct extent_state *other);
 void btrfs_split_delalloc_extent(struct inode *inode,
 				 struct extent_state *orig, u64 split);
-int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
-			 size_t size, struct bio *bio,
-			 unsigned long bio_flags);
+int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
+			     unsigned long bio_flags);
 void btrfs_set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end);
 vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf);
 int btrfs_readpage(struct file *file, struct page *page);

fs/btrfs/extent_io.c

@@ -2759,8 +2759,8 @@ static int submit_extent_page(unsigned int opf, struct extent_io_tree *tree,
 		else
 			contig = bio_end_sector(bio) == sector;
 
-		if (tree->ops && btrfs_merge_bio_hook(page, offset, page_size,
-						      bio, bio_flags))
+		ASSERT(tree->ops);
+		if (btrfs_bio_fits_in_stripe(page, page_size, bio, bio_flags))
 			can_merge = false;
 
 		if (prev_bio_flags != bio_flags || !contig || !can_merge ||

fs/btrfs/inode.c

@@ -1870,16 +1870,21 @@ void btrfs_clear_delalloc_extent(struct inode *vfs_inode,
 }
 
 /*
- * Merge bio hook, this must check the chunk tree to make sure we don't create
- * bios that span stripes or chunks
+ * btrfs_bio_fits_in_stripe - Checks whether the size of the given bio will fit
+ * in a chunk's stripe. This function ensures that bios do not span a
+ * stripe/chunk
  *
- * return 1 if page cannot be merged to bio
- * return 0 if page can be merged to bio
+ * @page - The page we are about to add to the bio
+ * @size - size we want to add to the bio
+ * @bio - bio we want to ensure is smaller than a stripe
+ * @bio_flags - flags of the bio
+ *
+ * return 1 if page cannot be added to the bio
+ * return 0 if page can be added to the bio
  * return error otherwise
  */
-int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
-			 size_t size, struct bio *bio,
-			 unsigned long bio_flags)
+int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
+			     unsigned long bio_flags)
 {
 	struct inode *inode = page->mapping->host;
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);

fs/btrfs/volumes.c

@@ -6136,8 +6136,10 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info,
 		*length = em->len - offset;
 	}
 
-	/* This is for when we're called from btrfs_merge_bio_hook() and all
-	   it cares about is the length */
+	/*
+	 * This is for when we're called from btrfs_bio_fits_in_stripe and all
+	 * it cares about is the length
+	 */
 	if (!bbio_ret)
 		goto out;