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, 37 insertions, 1 deletions

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 9facb4dc5c70..1f25c644cb12 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -31,6 +31,42 @@
 #include "xattr.h"
 #include "acl.h"
 
+#ifdef CONFIG_FS_DAX
+static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	ssize_t ret;
+
+	inode_lock_shared(inode);
+	/*
+	 * Recheck under inode lock - at this point we are sure it cannot
+	 * change anymore
+	 */
+	if (!IS_DAX(inode)) {
+		inode_unlock_shared(inode);
+		/* Fallback to buffered IO in case we cannot support DAX */
+		return generic_file_read_iter(iocb, to);
+	}
+	ret = dax_iomap_rw(iocb, to, &ext4_iomap_ops);
+	inode_unlock_shared(inode);
+
+	file_accessed(iocb->ki_filp);
+	return ret;
+}
+#endif
+
+static ssize_t ext4_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	if (!iov_iter_count(to))
+		return 0; /* skip atime */
+
+#ifdef CONFIG_FS_DAX
+	if (IS_DAX(file_inode(iocb->ki_filp)))
+		return ext4_dax_read_iter(iocb, to);
+#endif
+	return generic_file_read_iter(iocb, to);
+}
+
 /*
  * Called when an inode is released. Note that this is different
  * from ext4_file_open: open gets called at every open, but release
@@ -690,7 +726,7 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int whence)
 
 const struct file_operations ext4_file_operations = {
 	.llseek		= ext4_llseek,
-	.read_iter	= generic_file_read_iter,
+	.read_iter	= ext4_file_read_iter,
 	.write_iter	= ext4_file_write_iter,
 	.unlocked_ioctl = ext4_ioctl,
 #ifdef CONFIG_COMPAT