ovl: generalize the lower_fs[] array

Rename lower_fs[] array to fs[], extend its size by one and use index fsid
(instead of fsid-1) to access the fs[] array.

Initialize fs[0] with upper fs values. fsid 0 is reserved even with lower
only overlay, so fs[0] remains null in this case.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/inode.c

@@ -75,8 +75,7 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 	return err;
 }
 
-static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat,
-			   struct ovl_layer *lower_layer)
+static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat, int fsid)
 {
 	bool samefs = ovl_same_fs(dentry->d_sb);
 	unsigned int xinobits = ovl_xino_bits(dentry->d_sb);
@@ -103,9 +102,7 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat,
 			pr_warn_ratelimited("inode number too big (%pd2, ino=%llu, xinobits=%d)\n",
 					    dentry, stat->ino, xinobits);
 		} else {
-			if (lower_layer)
-				stat->ino |= ((u64)lower_layer->fsid) << shift;
-
+			stat->ino |= ((u64)fsid) << shift;
 			stat->dev = dentry->d_sb->s_dev;
 			return 0;
 		}
@@ -124,7 +121,7 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat,
 		 */
 		stat->dev = dentry->d_sb->s_dev;
 		stat->ino = dentry->d_inode->i_ino;
-	} else if (lower_layer && lower_layer->fsid) {
+	} else if (fsid) {
 		/*
 		 * For non-samefs setup, if we cannot map all layers st_ino
 		 * to a unified address space, we need to make sure that st_dev
@@ -132,7 +129,7 @@ static int ovl_map_dev_ino(struct dentry *dentry, struct kstat *stat,
 		 * lower layers use the unique anonymous bdev assigned to the
 		 * lower fs.
 		 */
-		stat->dev = lower_layer->fs->pseudo_dev;
+		stat->dev = OVL_FS(dentry->d_sb)->fs[fsid].pseudo_dev;
 	}
 
 	return 0;
@@ -147,7 +144,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 	const struct cred *old_cred;
 	bool is_dir = S_ISDIR(dentry->d_inode->i_mode);
 	bool samefs = ovl_same_fs(dentry->d_sb);
-	struct ovl_layer *lower_layer = NULL;
+	int fsid = 0;
 	int err;
 	bool metacopy_blocks = false;
 
@@ -170,7 +167,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 	 */
 	if (!is_dir || ovl_same_dev(dentry->d_sb)) {
 		if (!OVL_TYPE_UPPER(type)) {
-			lower_layer = ovl_layer_lower(dentry);
+			fsid = ovl_layer_lower(dentry)->fsid;
 		} else if (OVL_TYPE_ORIGIN(type)) {
 			struct kstat lowerstat;
 			u32 lowermask = STATX_INO | STATX_BLOCKS |
@@ -200,13 +197,13 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 			if (ovl_test_flag(OVL_INDEX, d_inode(dentry)) ||
 			    (!ovl_verify_lower(dentry->d_sb) &&
 			     (is_dir || lowerstat.nlink == 1))) {
-				lower_layer = ovl_layer_lower(dentry);
+				fsid = ovl_layer_lower(dentry)->fsid;
 				/*
 				 * Cannot use origin st_dev;st_ino because
 				 * origin inode content may differ from overlay
 				 * inode content.
 				 */
-				if (samefs || lower_layer->fsid)
+				if (samefs || fsid)
 					stat->ino = lowerstat.ino;
 			}
 
@@ -241,7 +238,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 		}
 	}
 
-	err = ovl_map_dev_ino(dentry, stat, lower_layer);
+	err = ovl_map_dev_ino(dentry, stat, fsid);
 	if (err)
 		goto out;
 

fs/overlayfs/ovl_entry.h

@@ -46,10 +46,10 @@ struct ovl_path {
 struct ovl_fs {
 	struct vfsmount *upper_mnt;
 	unsigned int numlayer;
-	/* Number of unique lower sb that differ from upper sb */
-	unsigned int numlowerfs;
+	/* Number of unique fs among layers including upper fs */
+	unsigned int numfs;
 	struct ovl_layer *layers;
-	struct ovl_sb *lower_fs;
+	struct ovl_sb *fs;
 	/* workbasedir is the path at workdir= mount option */
 	struct dentry *workbasedir;
 	/* workdir is the 'work' directory under workbasedir */

fs/overlayfs/super.c

@@ -228,10 +228,11 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 		iput(ofs->layers[i].trap);
 		mntput(ofs->layers[i].mnt);
 	}
-	for (i = 0; i < ofs->numlowerfs; i++)
-		free_anon_bdev(ofs->lower_fs[i].pseudo_dev);
 	kfree(ofs->layers);
-	kfree(ofs->lower_fs);
+	/* fs[0].pseudo_dev is either null or real upper st_dev */
+	for (i = 1; i < ofs->numfs; i++)
+		free_anon_bdev(ofs->fs[i].pseudo_dev);
+	kfree(ofs->fs);
 
 	kfree(ofs->config.lowerdir);
 	kfree(ofs->config.upperdir);
@@ -1259,7 +1260,7 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
 	if (!ofs->config.nfs_export && !ofs->upper_mnt)
 		return true;
 
-	for (i = 0; i < ofs->numlowerfs; i++) {
+	for (i = 1; i < ofs->numfs; i++) {
 		/*
 		 * We use uuid to associate an overlay lower file handle with a
 		 * lower layer, so we can accept lower fs with null uuid as long
@@ -1267,8 +1268,8 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
 		 * if we detect multiple lower fs with the same uuid, we
 		 * disable lower file handle decoding on all of them.
 		 */
-		if (uuid_equal(&ofs->lower_fs[i].sb->s_uuid, uuid)) {
-			ofs->lower_fs[i].bad_uuid = true;
+		if (uuid_equal(&ofs->fs[i].sb->s_uuid, uuid)) {
+			ofs->fs[i].bad_uuid = true;
 			return false;
 		}
 	}
@@ -1284,13 +1285,9 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 	int err;
 	bool bad_uuid = false;
 
-	/* fsid 0 is reserved for upper fs even with non upper overlay */
-	if (ofs->upper_mnt && ofs->upper_mnt->mnt_sb == sb)
-		return 0;
-
-	for (i = 0; i < ofs->numlowerfs; i++) {
-		if (ofs->lower_fs[i].sb == sb)
-			return i + 1;
+	for (i = 0; i < ofs->numfs; i++) {
+		if (ofs->fs[i].sb == sb)
+			return i;
 	}
 
 	if (!ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
@@ -1311,12 +1308,11 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 		return err;
 	}
 
-	ofs->lower_fs[ofs->numlowerfs].sb = sb;
-	ofs->lower_fs[ofs->numlowerfs].pseudo_dev = dev;
-	ofs->lower_fs[ofs->numlowerfs].bad_uuid = bad_uuid;
-	ofs->numlowerfs++;
+	ofs->fs[ofs->numfs].sb = sb;
+	ofs->fs[ofs->numfs].pseudo_dev = dev;
+	ofs->fs[ofs->numfs].bad_uuid = bad_uuid;
 
-	return ofs->numlowerfs;
+	return ofs->numfs++;
 }
 
 static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
@@ -1331,17 +1327,27 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 	if (ofs->layers == NULL)
 		goto out;
 
-	ofs->lower_fs = kcalloc(numlower, sizeof(struct ovl_sb),
-				GFP_KERNEL);
-	if (ofs->lower_fs == NULL)
+	ofs->fs = kcalloc(numlower + 1, sizeof(struct ovl_sb), GFP_KERNEL);
+	if (ofs->fs == NULL)
 		goto out;
 
-	/* idx 0 is reserved for upper fs even with lower only overlay */
+	/* idx/fsid 0 are reserved for upper fs even with lower only overlay */
+	ofs->numfs++;
+
 	ofs->layers[0].mnt = ofs->upper_mnt;
 	ofs->layers[0].idx = 0;
 	ofs->layers[0].fsid = 0;
 	ofs->numlayer = 1;
 
+	/*
+	 * All lower layers that share the same fs as upper layer, use the real
+	 * upper st_dev.
+	 */
+	if (ofs->upper_mnt) {
+		ofs->fs[0].sb = ofs->upper_mnt->mnt_sb;
+		ofs->fs[0].pseudo_dev = ofs->upper_mnt->mnt_sb->s_dev;
+	}
+
 	for (i = 0; i < numlower; i++) {
 		struct vfsmount *mnt;
 		struct inode *trap;
@@ -1379,10 +1385,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 		ofs->layers[ofs->numlayer].mnt = mnt;
 		ofs->layers[ofs->numlayer].idx = ofs->numlayer;
 		ofs->layers[ofs->numlayer].fsid = fsid;
-		if (fsid) {
-			ofs->layers[ofs->numlayer].fs =
-				&ofs->lower_fs[fsid - 1];
-		}
+		ofs->layers[ofs->numlayer].fs = &ofs->fs[fsid];
 		ofs->numlayer++;
 	}
 
@@ -1394,18 +1397,18 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 	 * bits reserved for fsid, it emits a warning and uses the original
 	 * inode number.
 	 */
-	if (!ofs->numlowerfs || (ofs->numlowerfs == 1 && !ofs->upper_mnt)) {
+	if (ofs->numfs - !ofs->upper_mnt == 1) {
 		if (ofs->config.xino == OVL_XINO_ON)
 			pr_info("\"xino=on\" is useless with all layers on same fs, ignore.\n");
 		ofs->xino_mode = 0;
 	} else if (ofs->config.xino == OVL_XINO_ON && ofs->xino_mode < 0) {
 		/*
-		 * This is a roundup of number of bits needed for numlowerfs+1
-		 * (i.e. ilog2(numlowerfs+1 - 1) + 1). fsid 0 is reserved for
-		 * upper fs even with non upper overlay.
+		 * This is a roundup of number of bits needed for encoding
+		 * fsid, where fsid 0 is reserved for upper fs even with
+		 * lower only overlay.
 		 */
 		BUILD_BUG_ON(ilog2(OVL_MAX_STACK) > 31);
-		ofs->xino_mode = ilog2(ofs->numlowerfs) + 1;
+		ofs->xino_mode = ilog2(ofs->numfs - 1) + 1;
 	}
 
 	if (ofs->xino_mode > 0) {