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>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 821719c..460d866 100644 (file)
--- 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: