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, 19 insertions, 13 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 96d62d97694e..5dacfa1fb129 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1598,25 +1598,31 @@ retry:
 }
 EXPORT_SYMBOL(iput);
 
+#ifdef CONFIG_BLOCK
 /**
  *	bmap	- find a block number in a file
- *	@inode: inode of file
- *	@block: block to find
- *
- *	Returns the block number on the device holding the inode that
- *	is the disk block number for the block of the file requested.
- *	That is, asked for block 4 of inode 1 the function will return the
- *	disk block relative to the disk start that holds that block of the
- *	file.
+ *	@inode:  inode owning the block number being requested
+ *	@block: pointer containing the block to find
+ *
+ *	Replaces the value in *block with the block number on the device holding
+ *	corresponding to the requested block number in the file.
+ *	That is, asked for block 4 of inode 1 the function will replace the
+ *	4 in *block, with disk block relative to the disk start that holds that
+ *	block of the file.
+ *
+ *	Returns -EINVAL in case of error, 0 otherwise. If mapping falls into a
+ *	hole, returns 0 and *block is also set to 0.
  */
-sector_t bmap(struct inode *inode, sector_t block)
+int bmap(struct inode *inode, sector_t *block)
 {
-	sector_t res = 0;
-	if (inode->i_mapping->a_ops->bmap)
-		res = inode->i_mapping->a_ops->bmap(inode->i_mapping, block);
-	return res;
+	if (!inode->i_mapping->a_ops->bmap)
+		return -EINVAL;
+
+	*block = inode->i_mapping->a_ops->bmap(inode->i_mapping, *block);
+	return 0;
 }
 EXPORT_SYMBOL(bmap);
+#endif
 
 /*
  * With relative atime, only update atime if the previous atime is