Route opens through fs_bdev_file_open_by_path() so each external device
is registered against the correct superblock, and convert the matching
releases.

Gao Xiang: I think typical immutable filesystems don't need .shutdown()
and .remove_bdev() for the following reasons:

  - blk_mark_disk_dead() sets GD_DEAD in advance of fs_bdev_mark_dead()
    so that the following bios will fail immediately; block_device
    references are still valid so it seems overkill to handle dead
    blockdevs in the deep filesystem I/O submission path.

  - Immutable filesystems like EROFS don't have write paths and journals,
    so they don't need to block writes (i.e., new dirty pages), metadata
    changes, and abort journals.

  - The comment above loop_change_fd() documents a valid read-only use
    case we need to support anyway, but it calls disk_force_media_change()
    which will call fs_bdev_mark_dead() later: we don't want loop_change_fd()
    shutdowns the active filesystems and return -EIO unconditionally.

Currently I think the default behavior (shrink_dcache_sb + evict_inodes)
in fs_bdev_mark_dead() is enough for immutable filesystems, tried to
document in the commit here for later reference.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/erofs/super.c | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 802add6652fd..def9cbfbc9d8 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -153,8 +153,8 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
 	} else if (!sbi->devs->flatdev) {
 		file = erofs_is_fileio_mode(sbi) ?
 				filp_open(dif->path, O_RDONLY | O_LARGEFILE, 0) :
-				bdev_file_open_by_path(dif->path,
-						BLK_OPEN_READ, sb->s_type, NULL);
+				fs_bdev_file_open_by_path(dif->path,
+						BLK_OPEN_READ, sb->s_type, sb);
 		if (IS_ERR(file)) {
 			if (file == ERR_PTR(-ENOTBLK))
 				return -EINVAL;
@@ -843,11 +843,16 @@ static int erofs_fc_reconfigure(struct fs_context *fc)
 
 static int erofs_release_device_info(int id, void *ptr, void *data)
 {
+	struct super_block *sb = data;
 	struct erofs_device_info *dif = ptr;
 
 	fs_put_dax(dif->dax_dev, NULL);
-	if (dif->file)
-		fput(dif->file);
+	if (dif->file) {
+		if (S_ISBLK(file_inode(dif->file)->i_mode))
+			fs_bdev_file_release(dif->file, sb);
+		else
+			fput(dif->file);
+	}
 	erofs_fscache_unregister_cookie(dif->fscache);
 	dif->fscache = NULL;
 	kfree(dif->path);
@@ -855,18 +860,19 @@ static int erofs_release_device_info(int id, void *ptr, void *data)
 	return 0;
 }
 
-static void erofs_free_dev_context(struct erofs_dev_context *devs)
+static void erofs_free_dev_context(struct erofs_dev_context *devs,
+				   struct super_block *sb)
 {
 	if (!devs)
 		return;
-	idr_for_each(&devs->tree, &erofs_release_device_info, NULL);
+	idr_for_each(&devs->tree, &erofs_release_device_info, sb);
 	idr_destroy(&devs->tree);
 	kfree(devs);
 }
 
-static void erofs_sb_free(struct erofs_sb_info *sbi)
+static void erofs_sb_free(struct erofs_sb_info *sbi, struct super_block *sb)
 {
-	erofs_free_dev_context(sbi->devs);
+	erofs_free_dev_context(sbi->devs, sb);
 	kfree(sbi->fsid);
 	kfree_sensitive(sbi->domain_id);
 	if (sbi->dif0.file)
@@ -879,8 +885,13 @@ static void erofs_fc_free(struct fs_context *fc)
 {
 	struct erofs_sb_info *sbi = fc->s_fs_info;
 
-	if (sbi) /* free here if an error occurs before transferring to sb */
-		erofs_sb_free(sbi);
+	/*
+	 * Freed here only if an error occurs before the sb is set up; at that
+	 * point no block-backed device has been claimed (that happens in
+	 * fill_super), so the NULL sb never reaches fs_bdev_file_release().
+	 */
+	if (sbi)
+		erofs_sb_free(sbi, NULL);
 }
 
 static const struct fs_context_operations erofs_context_ops = {
@@ -936,7 +947,7 @@ static void erofs_kill_sb(struct super_block *sb)
 	erofs_drop_internal_inodes(sbi);
 	fs_put_dax(sbi->dif0.dax_dev, NULL);
 	erofs_fscache_unregister_fs(sb);
-	erofs_sb_free(sbi);
+	erofs_sb_free(sbi, sb);
 	sb->s_fs_info = NULL;
 }
 
@@ -948,7 +959,7 @@ static void erofs_put_super(struct super_block *sb)
 	erofs_shrinker_unregister(sb);
 	erofs_xattr_prefixes_cleanup(sb);
 	erofs_drop_internal_inodes(sbi);
-	erofs_free_dev_context(sbi->devs);
+	erofs_free_dev_context(sbi->devs, sb);
 	sbi->devs = NULL;
 	erofs_fscache_unregister_fs(sb);
 }

-- 
2.47.3