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>

5 files changed, 60 insertions, 30 deletions

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 485db813d657b..00e1bf922fe2a 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3882,12 +3882,16 @@ static int check_swap_activate(struct swap_info_struct *sis,
 			page_no < sis->max) {
 		unsigned block_in_page;
 		sector_t first_block;
+		sector_t block = 0;
+		int	 err = 0;
 
 		cond_resched();
 
-		first_block = bmap(inode, probe_block);
-		if (first_block == 0)
+		block = probe_block;
+		err = bmap(inode, &block);
+		if (err || !block)
 			goto bad_bmap;
+		first_block = block;
 
 		/*
 		 * It must be PAGE_SIZE aligned on-disk
@@ -3899,11 +3903,13 @@ static int check_swap_activate(struct swap_info_struct *sis,
 
 		for (block_in_page = 1; block_in_page < blocks_per_page;
 					block_in_page++) {
-			sector_t block;
 
-			block = bmap(inode, probe_block + block_in_page);
-			if (block == 0)
+			block = probe_block + block_in_page;
+			err = bmap(inode, &block);
+
+			if (err || !block)
 				goto bad_bmap;
+
 			if (block != first_block + block_in_page) {
 				/* Discontiguity */
 				probe_block++;
diff --git a/fs/inode.c b/fs/inode.c
index 01ed6d0a4a5c6..935262dd04890 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1545,25 +1545,31 @@ 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
 
 /*
  * Update times in overlayed inode from underlying real inode
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 7d5ef3bf3f3e0..61e0bdd1a615c 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -801,18 +801,23 @@ int jbd2_journal_bmap(journal_t *journal, unsigned long blocknr,
 {
 	int err = 0;
 	unsigned long long ret;
+	sector_t block = 0;
 
 	if (journal->j_inode) {
-		ret = bmap(journal->j_inode, blocknr);
-		if (ret)
-			*retp = ret;
-		else {
+		block = blocknr;
+		ret = bmap(journal->j_inode, &block);
+
+		if (ret || !block) {
 			printk(KERN_ALERT "%s: journal block not found "
 					"at offset %lu on %s\n",
 			       __func__, blocknr, journal->j_devname);
 			err = -EIO;
 			__journal_abort_soft(journal, err);
+
+		} else {
+			*retp = block;
 		}
+
 	} else {
 		*retp = blocknr; /* +journal->j_blk_offset */
 	}
@@ -1238,11 +1243,14 @@ journal_t *jbd2_journal_init_dev(struct block_device *bdev,
 journal_t *jbd2_journal_init_inode(struct inode *inode)
 {
 	journal_t *journal;
+	sector_t blocknr;
 	char *p;
-	unsigned long long blocknr;
+	int err = 0;
+
+	blocknr = 0;
+	err = bmap(inode, &blocknr);
 
-	blocknr = bmap(inode, 0);
-	if (!blocknr) {
+	if (err || !blocknr) {
 		pr_err("%s: Cannot locate journal superblock\n",
 			__func__);
 		return NULL;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c8517bf00d5f2..efe4f2956cde4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2724,9 +2724,16 @@ static inline ssize_t generic_write_sync(struct kiocb *iocb, ssize_t count)
 
 extern void emergency_sync(void);
 extern void emergency_remount(void);
+
 #ifdef CONFIG_BLOCK
-extern sector_t bmap(struct inode *, sector_t);
+extern int bmap(struct inode *inode, sector_t *block);
+#else
+static inline int bmap(struct inode *inode,  sector_t *block)
+{
+	return -EINVAL;
+}
 #endif
+
 extern int notify_change(struct dentry *, struct iattr *, struct inode **);
 extern int inode_permission(struct inode *, int);
 extern int __inode_permission(struct inode *, int);
diff --git a/mm/page_io.c b/mm/page_io.c
index 5d882de3fbfd2..989a4dda13d21 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -177,8 +177,9 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 
 		cond_resched();
 
-		first_block = bmap(inode, probe_block);
-		if (first_block == 0)
+		first_block = probe_block;
+		ret = bmap(inode, &first_block);
+		if (ret || !first_block)
 			goto bad_bmap;
 
 		/*
@@ -193,9 +194,11 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 					block_in_page++) {
 			sector_t block;
 
-			block = bmap(inode, probe_block + block_in_page);
-			if (block == 0)
+			block = probe_block + block_in_page;
+			ret = bmap(inode, &block);
+			if (ret || !block)
 				goto bad_bmap;
+
 			if (block != first_block + block_in_page) {
 				/* Discontiguity */
 				probe_block++;