ovl: add mutli-layer infrastructure

Add multiple lower layers to 'struct ovl_fs' and 'struct ovl_entry'.

ovl_entry will have an array of paths, instead of just the dentry.  This
allows a compact array containing just the layers which exist at current
point in the tree (which is expected to be a small number for the majority
of dentries).

The number of layers is not limited by this infrastructure.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 64 insertions, 34 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 821719cc8537..460d866b97a2 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -35,7 +35,8 @@ struct ovl_config {
 /* private information held for overlayfs's superblock */
 struct ovl_fs {
         struct vfsmount *upper_mnt;
-        struct vfsmount *lower_mnt;
+        unsigned numlower;
+        struct vfsmount **lower_mnt;
         struct dentry *workdir;
         long lower_namelen;
         /* pathnames of lower and upper dirs, for show_options */
@@ -47,7 +48,6 @@ struct ovl_dir_cache;
 /* private information held for every overlayfs dentry */
 struct ovl_entry {
         struct dentry *__upperdentry;
-        struct dentry *lowerdentry;
         struct ovl_dir_cache *cache;
         union {
                 struct {
@@ -56,10 +56,16 @@ struct ovl_entry {
                 };
                 struct rcu_head rcu;
         };
+        unsigned numlower;
+        struct path lowerstack[];
 };
 
 const char *ovl_opaque_xattr = "trusted.overlay.opaque";
 
+static struct dentry *__ovl_dentry_lower(struct ovl_entry *oe)
+{
+        return oe->numlower ? oe->lowerstack[0].dentry : NULL;
+}
 
 enum ovl_path_type ovl_path_type(struct dentry *dentry)
 {
@@ -69,7 +75,7 @@ enum ovl_path_type ovl_path_type(struct dentry *dentry)
         if (oe->__upperdentry) {
                 type = __OVL_PATH_UPPER;
 
-                if (oe->lowerdentry) {
+                if (oe->numlower) {
                         if (S_ISDIR(dentry->d_inode->i_mode))
                                 type |= __OVL_PATH_MERGE;
                 } else if (!oe->opaque) {
@@ -117,7 +123,7 @@ struct dentry *ovl_dentry_lower(struct dentry *dentry)
 {
         struct ovl_entry *oe = dentry->d_fsdata;
 
-        return oe->lowerdentry;
+        return __ovl_dentry_lower(oe);
 }
 
 struct dentry *ovl_dentry_real(struct dentry *dentry)
@@ -127,7 +133,7 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)
 
         realdentry = ovl_upperdentry_dereference(oe);
         if (!realdentry)
-                realdentry = oe->lowerdentry;
+                realdentry = __ovl_dentry_lower(oe);
 
         return realdentry;
 }
@@ -140,7 +146,7 @@ struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
         if (realdentry) {
                 *is_upper = true;
         } else {
-                realdentry = oe->lowerdentry;
+                realdentry = __ovl_dentry_lower(oe);
                 *is_upper = false;
         }
         return realdentry;
@@ -162,11 +168,9 @@ void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
 
 void ovl_path_lower(struct dentry *dentry, struct path *path)
 {
-        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
         struct ovl_entry *oe = dentry->d_fsdata;
 
-        path->mnt = ofs->lower_mnt;
-        path->dentry = oe->lowerdentry;
+        *path = oe->numlower ? oe->lowerstack[0] : (struct path) { NULL, NULL };
 }
 
 int ovl_want_write(struct dentry *dentry)
@@ -258,8 +262,11 @@ static void ovl_dentry_release(struct dentry *dentry)
         struct ovl_entry *oe = dentry->d_fsdata;
 
         if (oe) {
+                unsigned int i;
+
                 dput(oe->__upperdentry);
-                dput(oe->lowerdentry);
+                for (i = 0; i < oe->numlower; i++)
+                        dput(oe->lowerstack[i].dentry);
                 kfree_rcu(oe, rcu);
         }
 }
@@ -268,9 +275,15 @@ static const struct dentry_operations ovl_dentry_operations = {
         .d_release = ovl_dentry_release,
 };
 
-static struct ovl_entry *ovl_alloc_entry(void)
+static struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 {
-        return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+        size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);
+        struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
+
+        if (oe)
+                oe->numlower = numlower;
+
+        return oe;
 }
 
 static inline struct dentry *ovl_lookup_real(struct dentry *dir,
@@ -297,19 +310,19 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 {
         struct ovl_entry *oe;
         struct dentry *upperdir;
-        struct dentry *lowerdir;
+        struct path lowerdir;
         struct dentry *upperdentry = NULL;
         struct dentry *lowerdentry = NULL;
         struct inode *inode = NULL;
         int err;
 
         err = -ENOMEM;
-        oe = ovl_alloc_entry();
+        oe = ovl_alloc_entry(1);
         if (!oe)
                 goto out;
 
         upperdir = ovl_dentry_upper(dentry->d_parent);
-        lowerdir = ovl_dentry_lower(dentry->d_parent);
+        ovl_path_lower(dentry->d_parent, &lowerdir);
 
         if (upperdir) {
                 upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
@@ -317,7 +330,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                 if (IS_ERR(upperdentry))
                         goto out_put_dir;
 
-                if (lowerdir && upperdentry) {
+                if (lowerdir.dentry && upperdentry) {
                         if (ovl_is_whiteout(upperdentry)) {
                                 dput(upperdentry);
                                 upperdentry = NULL;
@@ -327,8 +340,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                         }
                 }
         }
-        if (lowerdir && !oe->opaque) {
-                lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
+        if (lowerdir.dentry && !oe->opaque) {
+                lowerdentry = ovl_lookup_real(lowerdir.dentry, &dentry->d_name);
                 err = PTR_ERR(lowerdentry);
                 if (IS_ERR(lowerdentry))
                         goto out_dput_upper;
@@ -355,8 +368,12 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
         }
 
         oe->__upperdentry = upperdentry;
-        oe->lowerdentry = lowerdentry;
-
+        if (lowerdentry) {
+                oe->lowerstack[0].dentry = lowerdentry;
+                oe->lowerstack[0].mnt = lowerdir.mnt;
+        } else {
+                oe->numlower = 0;
+        }
         dentry->d_fsdata = oe;
         d_add(dentry, inode);
 
@@ -380,10 +397,12 @@ struct file *ovl_path_open(struct path *path, int flags)
 static void ovl_put_super(struct super_block *sb)
 {
         struct ovl_fs *ufs = sb->s_fs_info;
+        unsigned i;
 
         dput(ufs->workdir);
         mntput(ufs->upper_mnt);
-        mntput(ufs->lower_mnt);
+        for (i = 0; i < ufs->numlower; i++)
+                mntput(ufs->lower_mnt[i]);
 
         kfree(ufs->config.lowerdir);
         kfree(ufs->config.upperdir);
@@ -641,6 +660,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         struct ovl_entry *oe;
         struct ovl_fs *ufs;
         struct kstatfs statfs;
+        struct vfsmount *mnt;
+        unsigned int i;
         int err;
 
         err = -ENOMEM;
@@ -661,7 +682,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         }
 
         err = -ENOMEM;
-        oe = ovl_alloc_entry();
+        oe = ovl_alloc_entry(1);
         if (oe == NULL)
                 goto out_free_config;
 
@@ -727,12 +748,24 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 goto out_put_workpath;
         }
 
-        ufs->lower_mnt = clone_private_mount(&lowerpath);
-        err = PTR_ERR(ufs->lower_mnt);
-        if (IS_ERR(ufs->lower_mnt)) {
-                pr_err("overlayfs: failed to clone lowerpath\n");
+        ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);
+        if (ufs->lower_mnt == NULL)
                 goto out_put_upper_mnt;
+
+        mnt = clone_private_mount(&lowerpath);
+        err = PTR_ERR(mnt);
+        if (IS_ERR(mnt)) {
+                pr_err("overlayfs: failed to clone lowerpath\n");
+                goto out_put_lower_mnt;
         }
+        /*
+         * Make lower_mnt R/O.  That way fchmod/fchown on lower file
+         * will fail instead of modifying lower fs.
+         */
+        mnt->mnt_flags |= MNT_READONLY;
+
+        ufs->lower_mnt[0] = mnt;
+        ufs->numlower = 1;
 
         ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
         err = PTR_ERR(ufs->workdir);
@@ -742,12 +775,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 goto out_put_lower_mnt;
         }
 
-        /*
-         * Make lower_mnt R/O.  That way fchmod/fchown on lower file
-         * will fail instead of modifying lower fs.
-         */
-        ufs->lower_mnt->mnt_flags |= MNT_READONLY;
-
         /* If the upper fs is r/o, we mark overlayfs r/o too */
         if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
                 sb->s_flags |= MS_RDONLY;
@@ -768,7 +795,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         path_put(&workpath);
 
         oe->__upperdentry = upperpath.dentry;
-        oe->lowerdentry = lowerpath.dentry;
+        oe->lowerstack[0].dentry = lowerpath.dentry;
+        oe->lowerstack[0].mnt = ufs->lower_mnt[0];
 
         root_dentry->d_fsdata = oe;
 
@@ -782,7 +810,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 out_put_workdir:
         dput(ufs->workdir);
 out_put_lower_mnt:
-        mntput(ufs->lower_mnt);
+        for (i = 0; i < ufs->numlower; i++)
+                mntput(ufs->lower_mnt[i]);
+        kfree(ufs->lower_mnt);
 out_put_upper_mnt:
         mntput(ufs->upper_mnt);
 out_put_workpath: