ovl: allocate anon bdev per unique lower fs

Instead of allocating an anonymous bdev per lower layer, allocate
one anonymous bdev per every unique lower fs that is different than
upper fs.

Every unique lower fs is assigned an fsid > 0 and the number of
unique lower fs are stored in ofs->numlowerfs.

The assigned fsid is stored in the lower layer struct and will be
used also for inode number multiplexing.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index bfef6edcc111..e1c838c27a74 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -20,11 +20,18 @@ struct ovl_config {
 	bool nfs_export;
 };
 
+struct ovl_sb {
+	struct super_block *sb;
+	dev_t pseudo_dev;
+};
+
 struct ovl_layer {
 	struct vfsmount *mnt;
-	dev_t pseudo_dev;
-	/* Index of this layer in fs root (upper == 0) */
+	struct ovl_sb *fs;
+	/* Index of this layer in fs root (upper idx == 0) */
 	int idx;
+	/* One fsid per unique underlying sb (upper fsid == 0) */
+	int fsid;
 };
 
 struct ovl_path {
@@ -35,8 +42,11 @@ struct ovl_path {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
 	struct vfsmount *upper_mnt;
-	unsigned numlower;
+	unsigned int numlower;
+	/* Number of unique lower sb that differ from upper sb */
+	unsigned int numlowerfs;
 	struct ovl_layer *lower_layers;
+	struct ovl_sb *lower_fs;
 	/* workbasedir is the path at workdir= mount option */
 	struct dentry *workbasedir;
 	/* workdir is the 'work' directory under workbasedir */
@@ -50,8 +60,6 @@ struct ovl_fs {
 	const struct cred *creator_cred;
 	bool tmpfile;
 	bool noxattr;
-	/* sb common to all layers */
-	struct super_block *same_sb;
 	/* Did we take the inuse lock? */
 	bool upperdir_locked;
 	bool workdir_locked;