fs: Enable bmap() function to properly return errors

By now, bmap() will either return the physical block number related to
the requested file offset or 0 in case of error or the requested offset
maps into a hole.
This patch makes the needed changes to enable bmap() to proper return
errors, using the return value as an error return, and now, a pointer
must be passed to bmap() to be filled with the mapped physical block.

It will change the behavior of bmap() on return:

- negative value in case of error
- zero on success or map fell into a hole

In case of a hole, the *block will be zero too

Since this is a prep patch, by now, the only error return is -EINVAL if
->bmap doesn't exist.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 6 deletions

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 3ad18246fcb3..92d3b515252d 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -364,7 +364,7 @@ static int read_page(struct file *file, unsigned long index,
 	int ret = 0;
 	struct inode *inode = file_inode(file);
 	struct buffer_head *bh;
-	sector_t block;
+	sector_t block, blk_cur;
 
 	pr_debug("read bitmap file (%dB @ %llu)\n", (int)PAGE_SIZE,
 		 (unsigned long long)index << PAGE_SHIFT);
@@ -375,17 +375,21 @@ static int read_page(struct file *file, unsigned long index,
 		goto out;
 	}
 	attach_page_buffers(page, bh);
-	block = index << (PAGE_SHIFT - inode->i_blkbits);
+	blk_cur = index << (PAGE_SHIFT - inode->i_blkbits);
 	while (bh) {
+		block = blk_cur;
+
 		if (count == 0)
 			bh->b_blocknr = 0;
 		else {
-			bh->b_blocknr = bmap(inode, block);
-			if (bh->b_blocknr == 0) {
-				/* Cannot use this file! */
+			ret = bmap(inode, &block);
+			if (ret || !block) {
 				ret = -EINVAL;
+				bh->b_blocknr = 0;
 				goto out;
 			}
+
+			bh->b_blocknr = block;
 			bh->b_bdev = inode->i_sb->s_bdev;
 			if (count < (1<<inode->i_blkbits))
 				count = 0;
@@ -399,7 +403,7 @@ static int read_page(struct file *file, unsigned long index,
 			set_buffer_mapped(bh);
 			submit_bh(REQ_OP_READ, 0, bh);
 		}
-		block++;
+		blk_cur++;
 		bh = bh->b_this_page;
 	}
 	page->index = index;