ext4: convert DAX reads to iomap infrastructure

Implement basic iomap_begin function that handles reading and use it for
DAX reads.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 54 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 733fda1c3646..5e0526fed165 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -37,6 +37,7 @@
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/bitops.h>
+#include <linux/iomap.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -3318,6 +3319,59 @@ int ext4_dax_get_block(struct inode *inode, sector_t iblock,
 	clear_buffer_new(bh_result);
 	return 0;
 }
+
+static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
+			    unsigned flags, struct iomap *iomap)
+{
+	unsigned int blkbits = inode->i_blkbits;
+	unsigned long first_block = offset >> blkbits;
+	unsigned long last_block = (offset + length - 1) >> blkbits;
+	struct ext4_map_blocks map;
+	int ret;
+
+	if (flags & IOMAP_WRITE)
+		return -EIO;
+
+	if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
+		return -ERANGE;
+
+	map.m_lblk = first_block;
+	map.m_len = last_block - first_block + 1;
+
+	ret = ext4_map_blocks(NULL, inode, &map, 0);
+	if (ret < 0)
+		return ret;
+
+	iomap->flags = 0;
+	iomap->bdev = inode->i_sb->s_bdev;
+	iomap->offset = first_block << blkbits;
+
+	if (ret == 0) {
+		iomap->type = IOMAP_HOLE;
+		iomap->blkno = IOMAP_NULL_BLOCK;
+		iomap->length = (u64)map.m_len << blkbits;
+	} else {
+		if (map.m_flags & EXT4_MAP_MAPPED) {
+			iomap->type = IOMAP_MAPPED;
+		} else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
+			iomap->type = IOMAP_UNWRITTEN;
+		} else {
+			WARN_ON_ONCE(1);
+			return -EIO;
+		}
+		iomap->blkno = (sector_t)map.m_pblk << (blkbits - 9);
+		iomap->length = (u64)map.m_len << blkbits;
+	}
+
+	if (map.m_flags & EXT4_MAP_NEW)
+		iomap->flags |= IOMAP_F_NEW;
+	return 0;
+}
+
+struct iomap_ops ext4_iomap_ops = {
+	.iomap_begin		= ext4_iomap_begin,
+};
+
 #else
 /* Just define empty function, it will never get called. */
 int ext4_dax_get_block(struct inode *inode, sector_t iblock,