block: add a sb_open_mode helper

Add a helper to return the open flags for blkdev_get_by* for passed in
super block flags instead of open coding the logic in many places.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230608110258.189493-17-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/btrfs/super.c

@@ -1440,12 +1440,9 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
 	struct btrfs_fs_devices *fs_devices = NULL;
 	struct btrfs_fs_info *fs_info = NULL;
 	void *new_sec_opts = NULL;
-	fmode_t mode = FMODE_READ;
+	fmode_t mode = sb_open_mode(flags);
 	int error = 0;
 
-	if (!(flags & SB_RDONLY))
-		mode |= FMODE_WRITE;
-
 	if (data) {
 		error = security_sb_eat_lsm_opts(data, &new_sec_opts);
 		if (error)

fs/nilfs2/super.c

@@ -1278,14 +1278,11 @@ nilfs_mount(struct file_system_type *fs_type, int flags,
 {
 	struct nilfs_super_data sd;
 	struct super_block *s;
-	fmode_t mode = FMODE_READ;
 	struct dentry *root_dentry;
 	int err, s_new = false;
 
-	if (!(flags & SB_RDONLY))
-		mode |= FMODE_WRITE;
-
-	sd.bdev = blkdev_get_by_path(dev_name, mode, fs_type, NULL);
+	sd.bdev = blkdev_get_by_path(dev_name, sb_open_mode(flags), fs_type,
+				     NULL);
 	if (IS_ERR(sd.bdev))
 		return ERR_CAST(sd.bdev);
 

fs/super.c

@@ -1255,17 +1255,13 @@ int get_tree_bdev(struct fs_context *fc,
 {
 	struct block_device *bdev;
 	struct super_block *s;
-	fmode_t mode = FMODE_READ;
 	int error = 0;
 
-	if (!(fc->sb_flags & SB_RDONLY))
-		mode |= FMODE_WRITE;
-
 	if (!fc->source)
 		return invalf(fc, "No source specified");
 
-	bdev = blkdev_get_by_path(fc->source, mode, fc->fs_type,
-				  &fs_holder_ops);
+	bdev = blkdev_get_by_path(fc->source, sb_open_mode(fc->sb_flags),
+				  fc->fs_type, &fs_holder_ops);
 	if (IS_ERR(bdev)) {
 		errorf(fc, "%s: Can't open blockdev", fc->source);
 		return PTR_ERR(bdev);
@@ -1344,13 +1340,10 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 {
 	struct block_device *bdev;
 	struct super_block *s;
-	fmode_t mode = FMODE_READ;
 	int error = 0;
 
-	if (!(flags & SB_RDONLY))
-		mode |= FMODE_WRITE;
-
-	bdev = blkdev_get_by_path(dev_name, mode, fs_type, &fs_holder_ops);
+	bdev = blkdev_get_by_path(dev_name, sb_open_mode(flags), fs_type,
+				  &fs_holder_ops);
 	if (IS_ERR(bdev))
 		return ERR_CAST(bdev);
 

include/linux/blkdev.h

@@ -1473,6 +1473,13 @@ struct blk_holder_ops {
 	void (*mark_dead)(struct block_device *bdev);
 };
 
+/*
+ * Return the correct open flags for blkdev_get_by_* for super block flags
+ * as stored in sb->s_flags.
+ */
+#define sb_open_mode(flags) \
+	(FMODE_READ | (((flags) & SB_RDONLY) ? 0 : FMODE_WRITE))
+
 struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder,
 		const struct blk_holder_ops *hops);
 struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,