Re: [RFC PATCH] overlayfs: support more than one read-only layer

From: Miklos Szeredi
Date: Mon Nov 10 2014 - 04:10:37 EST

Thanks to everyone for testing.

Here's an updated patch to fix the statfs Oops.

Maybe it wasn't clear, but the number of lower layers isn't limited by
FILESYSTEM_MAX_STACK_DEPTH, only by the max size of the mount option buffer in
the kernel (1 page, usually 4096bytes). So you could have a hundred read-only
layers stacked in a single overlayfs mount.

As for changing the stacking while the overlayfs is mounted: currently this is
not supported, the layers specified at the mount time remain there until the
overlay is unmounted. Currently there's no possibility to add or remove layers
in a dynamic way, and it is definitely more tricky to implement than the static
configuration.

Thanks,
Miklos
----


diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index ea10a8719107..a5bfd60f4f6f 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -385,7 +385,7 @@ int ovl_copy_up(struct dentry *dentry)
struct kstat stat;
enum ovl_path_type type = ovl_path_type(dentry);

- if (type != OVL_PATH_LOWER)
+ if (OVL_TYPE_UPPER(type))
break;

next = dget(dentry);
@@ -394,7 +394,7 @@ int ovl_copy_up(struct dentry *dentry)
parent = dget_parent(next);

type = ovl_path_type(parent);
- if (type != OVL_PATH_LOWER)
+ if (OVL_TYPE_UPPER(type))
break;

dput(next);
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 15cd91ad9940..ab50bd111feb 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -152,7 +152,7 @@ static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
* correct link count. nlink=1 seems to pacify 'find' and
* other utilities.
*/
- if (type == OVL_PATH_MERGE)
+ if (OVL_TYPE_MERGE(type))
stat->nlink = 1;

return 0;
@@ -284,8 +284,7 @@ out:
return ERR_PTR(err);
}

-static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,
- enum ovl_path_type type)
+static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry)
{
int err;
struct dentry *ret = NULL;
@@ -294,8 +293,17 @@ static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,
err = ovl_check_empty_dir(dentry, &list);
if (err)
ret = ERR_PTR(err);
- else if (type == OVL_PATH_MERGE)
- ret = ovl_clear_empty(dentry, &list);
+ else {
+ /*
+ * If no upperdentry then skip clearing whiteouts.
+ *
+ * Can race with copy-up, since we don't hold the upperdir
+ * mutex. Doesn't matter, since copy-up can't create a
+ * non-empty directory from an empty one.
+ */
+ if (ovl_dentry_upper(dentry))
+ ret = ovl_clear_empty(dentry, &list);
+ }

ovl_cache_free(&list);

@@ -487,8 +495,7 @@ out:
return err;
}

-static int ovl_remove_and_whiteout(struct dentry *dentry,
- enum ovl_path_type type, bool is_dir)
+static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
{
struct dentry *workdir = ovl_workdir(dentry);
struct inode *wdir = workdir->d_inode;
@@ -500,7 +507,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
int err;

if (is_dir) {
- opaquedir = ovl_check_empty_and_clear(dentry, type);
+ opaquedir = ovl_check_empty_and_clear(dentry);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir))
goto out;
@@ -515,9 +522,10 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
if (IS_ERR(whiteout))
goto out_unlock;

- if (type == OVL_PATH_LOWER) {
+ upper = ovl_dentry_upper(dentry);
+ if (!upper) {
upper = lookup_one_len(dentry->d_name.name, upperdir,
- dentry->d_name.len);
+ dentry->d_name.len);
err = PTR_ERR(upper);
if (IS_ERR(upper))
goto kill_whiteout;
@@ -529,7 +537,6 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
} else {
int flags = 0;

- upper = ovl_dentry_upper(dentry);
if (opaquedir)
upper = opaquedir;
err = -ESTALE;
@@ -623,7 +630,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
goto out_drop_write;

type = ovl_path_type(dentry);
- if (type == OVL_PATH_PURE_UPPER) {
+ if (OVL_TYPE_PURE_UPPER(type)) {
err = ovl_remove_upper(dentry, is_dir);
} else {
const struct cred *old_cred;
@@ -648,7 +655,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
cap_raise(override_cred->cap_effective, CAP_CHOWN);
old_cred = override_creds(override_cred);

- err = ovl_remove_and_whiteout(dentry, type, is_dir);
+ err = ovl_remove_and_whiteout(dentry, is_dir);

revert_creds(old_cred);
put_cred(override_cred);
@@ -705,7 +712,7 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
/* Don't copy up directory trees */
old_type = ovl_path_type(old);
err = -EXDEV;
- if ((old_type == OVL_PATH_LOWER || old_type == OVL_PATH_MERGE) && is_dir)
+ if (OVL_TYPE_MERGE_OR_LOWER(old_type) && is_dir)
goto out;

if (new->d_inode) {
@@ -718,25 +725,25 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,

new_type = ovl_path_type(new);
err = -EXDEV;
- if (!overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir)
+ if (!overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir)
goto out;

err = 0;
- if (new_type == OVL_PATH_LOWER && old_type == OVL_PATH_LOWER) {
+ if (!OVL_TYPE_UPPER(new_type) && !OVL_TYPE_UPPER(old_type)) {
if (ovl_dentry_lower(old)->d_inode ==
ovl_dentry_lower(new)->d_inode)
goto out;
}
- if (new_type != OVL_PATH_LOWER && old_type != OVL_PATH_LOWER) {
+ if (OVL_TYPE_UPPER(new_type) && OVL_TYPE_UPPER(old_type)) {
if (ovl_dentry_upper(old)->d_inode ==
ovl_dentry_upper(new)->d_inode)
goto out;
}
} else {
if (ovl_dentry_is_opaque(new))
- new_type = OVL_PATH_UPPER;
+ new_type = __OVL_PATH_UPPER;
else
- new_type = OVL_PATH_PURE_UPPER;
+ new_type = __OVL_PATH_UPPER | __OVL_PATH_PURE;
}

err = ovl_want_write(old);
@@ -756,8 +763,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
goto out_drop_write;
}

- old_opaque = old_type != OVL_PATH_PURE_UPPER;
- new_opaque = new_type != OVL_PATH_PURE_UPPER;
+ old_opaque = !OVL_TYPE_PURE_UPPER(old_type);
+ new_opaque = !OVL_TYPE_PURE_UPPER(new_type);

if (old_opaque || new_opaque) {
err = -ENOMEM;
@@ -780,8 +787,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
old_cred = override_creds(override_cred);
}

- if (overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir) {
- opaquedir = ovl_check_empty_and_clear(new, new_type);
+ if (overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir) {
+ opaquedir = ovl_check_empty_and_clear(new);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir)) {
opaquedir = NULL;
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index af2d18c9fcee..48492f1240ad 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -235,26 +235,39 @@ out:
return err;
}

+static bool ovl_need_xattr_filter(struct dentry *dentry,
+ enum ovl_path_type type)
+{
+ if ((type & (__OVL_PATH_PURE | __OVL_PATH_UPPER)) == __OVL_PATH_UPPER)
+ return S_ISDIR(dentry->d_inode->i_mode);
+ else
+ return false;
+}
+
ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
void *value, size_t size)
{
- if (ovl_path_type(dentry->d_parent) == OVL_PATH_MERGE &&
- ovl_is_private_xattr(name))
+ struct path realpath;
+ enum ovl_path_type type = ovl_path_real(dentry, &realpath);
+
+ if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
return -ENODATA;

- return vfs_getxattr(ovl_dentry_real(dentry), name, value, size);
+ return vfs_getxattr(realpath.dentry, name, value, size);
}

ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
{
+ struct path realpath;
+ enum ovl_path_type type = ovl_path_real(dentry, &realpath);
ssize_t res;
int off;

- res = vfs_listxattr(ovl_dentry_real(dentry), list, size);
+ res = vfs_listxattr(realpath.dentry, list, size);
if (res <= 0 || size == 0)
return res;

- if (ovl_path_type(dentry->d_parent) != OVL_PATH_MERGE)
+ if (!ovl_need_xattr_filter(dentry, type))
return res;

/* filter out private xattrs */
@@ -279,18 +292,17 @@ int ovl_removexattr(struct dentry *dentry, const char *name)
{
int err;
struct path realpath;
- enum ovl_path_type type;
+ enum ovl_path_type type = ovl_path_real(dentry, &realpath);

err = ovl_want_write(dentry);
if (err)
goto out;

- if (ovl_path_type(dentry->d_parent) == OVL_PATH_MERGE &&
- ovl_is_private_xattr(name))
+ err = -ENODATA;
+ if (ovl_need_xattr_filter(dentry, type) && ovl_is_private_xattr(name))
goto out_drop_write;

- type = ovl_path_real(dentry, &realpath);
- if (type == OVL_PATH_LOWER) {
+ if (!OVL_TYPE_UPPER(type)) {
err = vfs_getxattr(realpath.dentry, name, NULL, 0);
if (err < 0)
goto out_drop_write;
@@ -312,7 +324,7 @@ out:
static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
struct dentry *realdentry)
{
- if (type != OVL_PATH_LOWER)
+ if (OVL_TYPE_UPPER(type))
return false;

if (special_file(realdentry->d_inode->i_mode))
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 814bed33dd07..5b59e7d0a03a 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -12,12 +12,17 @@
struct ovl_entry;

enum ovl_path_type {
- OVL_PATH_PURE_UPPER,
- OVL_PATH_UPPER,
- OVL_PATH_MERGE,
- OVL_PATH_LOWER,
+ __OVL_PATH_PURE = (1 << 0),
+ __OVL_PATH_UPPER = (1 << 1),
+ __OVL_PATH_MERGE = (1 << 2),
};

+#define OVL_TYPE_UPPER(type) ((type) & __OVL_PATH_UPPER)
+#define OVL_TYPE_MERGE(type) ((type) & __OVL_PATH_MERGE)
+#define OVL_TYPE_PURE_UPPER(type) ((type) & __OVL_PATH_PURE)
+#define OVL_TYPE_MERGE_OR_LOWER(type) \
+ (OVL_TYPE_MERGE(type) || !OVL_TYPE_UPPER(type))
+
extern const char *ovl_opaque_xattr;

static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
@@ -130,6 +135,7 @@ void ovl_dentry_version_inc(struct dentry *dentry);
void ovl_path_upper(struct dentry *dentry, struct path *path);
void ovl_path_lower(struct dentry *dentry, struct path *path);
enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path);
+int ovl_path_next(int *idx, struct dentry *dentry, struct path *path);
struct dentry *ovl_dentry_upper(struct dentry *dentry);
struct dentry *ovl_dentry_lower(struct dentry *dentry);
struct dentry *ovl_dentry_real(struct dentry *dentry);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 2a7ef4f8e2a6..8087b63ffc32 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -40,6 +40,7 @@ struct ovl_readdir_data {
struct rb_root root;
struct list_head *list;
struct list_head middle;
+ struct dentry *dir;
int count;
int err;
};
@@ -126,6 +127,32 @@ static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
if (p == NULL)
return -ENOMEM;

+ if (d_type == DT_CHR) {
+ struct dentry *dentry;
+ const struct cred *old_cred;
+ struct cred *override_cred;
+
+ override_cred = prepare_creds();
+ if (!override_cred) {
+ kfree(p);
+ return -ENOMEM;
+ }
+
+ /*
+ * CAP_DAC_OVERRIDE for lookup
+ */
+ cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+ old_cred = override_creds(override_cred);
+
+ dentry = lookup_one_len(name, rdd->dir, len);
+ if (!IS_ERR(dentry)) {
+ p->is_whiteout = ovl_is_whiteout(dentry);
+ dput(dentry);
+ }
+ revert_creds(old_cred);
+ put_cred(override_cred);
+ }
+
list_add_tail(&p->l_node, rdd->list);
rb_link_node(&p->node, parent, newp);
rb_insert_color(&p->node, &rdd->root);
@@ -226,88 +253,42 @@ static void ovl_dir_reset(struct file *file)
ovl_cache_put(od, dentry);
od->cache = NULL;
}
- WARN_ON(!od->is_real && type != OVL_PATH_MERGE);
- if (od->is_real && type == OVL_PATH_MERGE)
+ WARN_ON(!od->is_real && !OVL_TYPE_MERGE(type));
+ if (od->is_real && OVL_TYPE_MERGE(type))
od->is_real = false;
}

-static int ovl_dir_mark_whiteouts(struct dentry *dir,
- struct ovl_readdir_data *rdd)
-{
- struct ovl_cache_entry *p;
- struct dentry *dentry;
- const struct cred *old_cred;
- struct cred *override_cred;
-
- override_cred = prepare_creds();
- if (!override_cred) {
- ovl_cache_free(rdd->list);
- return -ENOMEM;
- }
-
- /*
- * CAP_DAC_OVERRIDE for lookup
- */
- cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
- old_cred = override_creds(override_cred);
-
- mutex_lock(&dir->d_inode->i_mutex);
- list_for_each_entry(p, rdd->list, l_node) {
- if (p->is_cursor)
- continue;
-
- if (p->type != DT_CHR)
- continue;
-
- dentry = lookup_one_len(p->name, dir, p->len);
- if (IS_ERR(dentry))
- continue;
-
- p->is_whiteout = ovl_is_whiteout(dentry);
- dput(dentry);
- }
- mutex_unlock(&dir->d_inode->i_mutex);
-
- revert_creds(old_cred);
- put_cred(override_cred);
-
- return 0;
-}
-
-static inline int ovl_dir_read_merged(struct path *upperpath,
- struct path *lowerpath,
- struct list_head *list)
+static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
{
int err;
+ struct path realpath;
struct ovl_readdir_data rdd = {
.ctx.actor = ovl_fill_merge,
.list = list,
.root = RB_ROOT,
.is_merge = false,
};
+ int idx, next;

- if (upperpath->dentry) {
- err = ovl_dir_read(upperpath, &rdd);
- if (err)
- goto out;
+ for (idx = 0; idx != -1; idx = next) {
+ next = ovl_path_next(&idx, dentry, &realpath);

- if (lowerpath->dentry) {
- err = ovl_dir_mark_whiteouts(upperpath->dentry, &rdd);
+ if (next != -1) {
+ rdd.dir = realpath.dentry;
+ err = ovl_dir_read(&realpath, &rdd);
if (err)
- goto out;
+ break;
+ } else {
+ /*
+ * Insert lowest layer entries before upper ones, this
+ * allows offsets to be reasonably constant
+ */
+ list_add(&rdd.middle, rdd.list);
+ rdd.is_merge = true;
+ err = ovl_dir_read(&realpath, &rdd);
+ list_del(&rdd.middle);
}
}
- if (lowerpath->dentry) {
- /*
- * Insert lowerpath entries before upperpath ones, this allows
- * offsets to be reasonably constant
- */
- list_add(&rdd.middle, rdd.list);
- rdd.is_merge = true;
- err = ovl_dir_read(lowerpath, &rdd);
- list_del(&rdd.middle);
- }
-out:
return err;
}

@@ -329,8 +310,6 @@ static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
{
int res;
- struct path lowerpath;
- struct path upperpath;
struct ovl_dir_cache *cache;

cache = ovl_dir_cache(dentry);
@@ -347,10 +326,7 @@ static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
cache->refcount = 1;
INIT_LIST_HEAD(&cache->entries);

- ovl_path_lower(dentry, &lowerpath);
- ovl_path_upper(dentry, &upperpath);
-
- res = ovl_dir_read_merged(&upperpath, &lowerpath, &cache->entries);
+ res = ovl_dir_read_merged(dentry, &cache->entries);
if (res) {
ovl_cache_free(&cache->entries);
kfree(cache);
@@ -452,10 +428,10 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
/*
* Need to check if we started out being a lower dir, but got copied up
*/
- if (!od->is_upper && ovl_path_type(dentry) == OVL_PATH_MERGE) {
+ if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
struct inode *inode = file_inode(file);

- realfile =lockless_dereference(od->upperfile);
+ realfile = lockless_dereference(od->upperfile);
if (!realfile) {
struct path upperpath;

@@ -518,8 +494,8 @@ static int ovl_dir_open(struct inode *inode, struct file *file)
}
INIT_LIST_HEAD(&od->cursor.l_node);
od->realfile = realfile;
- od->is_real = (type != OVL_PATH_MERGE);
- od->is_upper = (type != OVL_PATH_LOWER);
+ od->is_real = !OVL_TYPE_MERGE(type);
+ od->is_upper = OVL_TYPE_UPPER(type);
od->cursor.is_cursor = true;
file->private_data = od;

@@ -538,14 +514,9 @@ const struct file_operations ovl_dir_operations = {
int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
{
int err;
- struct path lowerpath;
- struct path upperpath;
struct ovl_cache_entry *p;

- ovl_path_upper(dentry, &upperpath);
- ovl_path_lower(dentry, &lowerpath);
-
- err = ovl_dir_read_merged(&upperpath, &lowerpath, list);
+ err = ovl_dir_read_merged(dentry, list);
if (err)
return err;

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 08b704cebfc4..0b679321452d 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -28,6 +28,7 @@ MODULE_LICENSE("GPL");

struct ovl_config {
char *lowerdir;
+ char *lowerdirs;
char *upperdir;
char *workdir;
};
@@ -35,7 +36,8 @@ 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 +49,6 @@ 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 {
@@ -56,40 +57,41 @@ 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)
{
struct ovl_entry *oe = dentry->d_fsdata;
+ enum ovl_path_type type = 0;

if (oe->__upperdentry) {
- if (oe->lowerdentry) {
+ type = __OVL_PATH_UPPER;
+
+ if (oe->numlower) {
if (S_ISDIR(dentry->d_inode->i_mode))
- return OVL_PATH_MERGE;
- else
- return OVL_PATH_UPPER;
- } else {
- if (oe->opaque)
- return OVL_PATH_UPPER;
- else
- return OVL_PATH_PURE_UPPER;
+ type |= __OVL_PATH_MERGE;
+ } else if (!oe->opaque) {
+ type |= __OVL_PATH_PURE;
}
} else {
- return OVL_PATH_LOWER;
+ if (oe->numlower > 1)
+ type |= __OVL_PATH_MERGE;
}
+ return type;
}

static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
{
- struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
- /*
- * Make sure to order reads to upperdentry wrt ovl_dentry_update()
- */
- smp_read_barrier_depends();
- return upperdentry;
+ return lockless_dereference(oe->__upperdentry);
}

void ovl_path_upper(struct dentry *dentry, struct path *path)
@@ -106,7 +108,7 @@ enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)

enum ovl_path_type type = ovl_path_type(dentry);

- if (type == OVL_PATH_LOWER)
+ if (!OVL_TYPE_UPPER(type))
ovl_path_lower(dentry, path);
else
ovl_path_upper(dentry, path);
@@ -125,7 +127,7 @@ 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)
@@ -135,7 +137,7 @@ 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;
}
@@ -148,7 +150,7 @@ 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;
@@ -170,11 +172,9 @@ 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)
@@ -266,8 +266,11 @@ 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);
}
}
@@ -276,9 +279,15 @@ 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,
@@ -300,82 +309,129 @@ static inline struct dentry *ovl_lookup_real(struct dentry *dir,
return dentry;
}

+/*
+ * Returns next layer in stack starting from top.
+ * Modifies idx, so that caller can check for upper layer -> idx == 0.
+ * Returns next index or -1 if this is the last layer.
+ */
+int ovl_path_next(int *idx, struct dentry *dentry, struct path *path)
+{
+ struct ovl_entry *oe = dentry->d_fsdata;
+
+ BUG_ON(*idx < 0);
+ if (*idx == 0) {
+ ovl_path_upper(dentry, path);
+ if (path->dentry)
+ return oe->numlower ? 1 : -1;
+ (*idx)++;
+ }
+ BUG_ON(*idx > oe->numlower);
+ *path = oe->lowerstack[*idx - 1];
+
+ return (*idx < oe->numlower) ? *idx + 1 : -1;
+}
+
struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
unsigned int flags)
{
struct ovl_entry *oe;
- struct dentry *upperdir;
- struct dentry *lowerdir;
- struct dentry *upperdentry = NULL;
- struct dentry *lowerdentry = NULL;
+ struct ovl_entry *poe = dentry->d_parent->d_fsdata;
+ struct path *stack;
+ unsigned int ctr = 0;
+ unsigned int loweroffset = 0;
struct inode *inode = NULL;
+ bool upperopaque = false;
+ struct dentry *prev = NULL;
+ int idx, next;
+ unsigned int i;
int err;

err = -ENOMEM;
- oe = ovl_alloc_entry();
- if (!oe)
+ stack = kcalloc(poe->numlower + 1, sizeof(struct path), GFP_KERNEL);
+ if (!stack)
goto out;

- upperdir = ovl_dentry_upper(dentry->d_parent);
- lowerdir = ovl_dentry_lower(dentry->d_parent);
-
- if (upperdir) {
- upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
- err = PTR_ERR(upperdentry);
- if (IS_ERR(upperdentry))
- goto out_put_dir;
-
- if (lowerdir && upperdentry) {
- if (ovl_is_whiteout(upperdentry)) {
- dput(upperdentry);
- upperdentry = NULL;
- oe->opaque = true;
- } else if (ovl_is_opaquedir(upperdentry)) {
- oe->opaque = true;
+ for (idx = 0; idx != -1; idx = next) {
+ struct dentry *this;
+ struct path dir;
+ bool opaque = false;
+
+ next = ovl_path_next(&idx, dentry->d_parent, &dir);
+
+ this = ovl_lookup_real(dir.dentry, &dentry->d_name);
+ err = PTR_ERR(this);
+ if (IS_ERR(this))
+ goto out_put;
+
+ /*
+ * If this is not the lowermost layer, check whiteout and opaque
+ * directory.
+ */
+ if (next != -1 && this) {
+ if (ovl_is_whiteout(this)) {
+ dput(this);
+ this = NULL;
+ opaque = true;
+ } else if (ovl_is_opaquedir(this)) {
+ opaque = true;
}
+ if (opaque && idx == 0)
+ upperopaque = true;
}
+ if (this && prev && (!S_ISDIR(prev->d_inode->i_mode) ||
+ !S_ISDIR(this->d_inode->i_mode))) {
+ dput(this);
+ this = NULL;
+ opaque = true;
+ if (loweroffset && prev == stack[0].dentry)
+ upperopaque = true;
+ }
+ if (this) {
+ stack[ctr].dentry = this;
+ stack[ctr].mnt = dir.mnt;
+ ctr++;
+ prev = this;
+ if (idx == 0)
+ loweroffset = 1;
+ }
+ if (opaque)
+ break;
}
- if (lowerdir && !oe->opaque) {
- lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
- err = PTR_ERR(lowerdentry);
- if (IS_ERR(lowerdentry))
- goto out_dput_upper;
- }
-
- if (lowerdentry && upperdentry &&
- (!S_ISDIR(upperdentry->d_inode->i_mode) ||
- !S_ISDIR(lowerdentry->d_inode->i_mode))) {
- dput(lowerdentry);
- lowerdentry = NULL;
- oe->opaque = true;
- }
+ oe = ovl_alloc_entry(ctr - loweroffset);
+ err = -ENOMEM;
+ if (!oe)
+ goto out_put;

- if (lowerdentry || upperdentry) {
- struct dentry *realdentry;
+ if (ctr) {
+ struct dentry *realdentry = stack[0].dentry;

- realdentry = upperdentry ? upperdentry : lowerdentry;
err = -ENOMEM;
inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
oe);
if (!inode)
- goto out_dput;
+ goto out_free_oe;
ovl_copyattr(realdentry->d_inode, inode);
}

- oe->__upperdentry = upperdentry;
- oe->lowerdentry = lowerdentry;
-
+ oe->opaque = upperopaque;
+ if (loweroffset)
+ oe->__upperdentry = stack[0].dentry;
+ if (oe->numlower) {
+ memcpy(oe->lowerstack, stack + loweroffset,
+ sizeof(struct path) * oe->numlower);
+ }
+ kfree(stack);
dentry->d_fsdata = oe;
d_add(dentry, inode);

return NULL;

-out_dput:
- dput(lowerdentry);
-out_dput_upper:
- dput(upperdentry);
-out_put_dir:
+out_free_oe:
kfree(oe);
+out_put:
+ for (i = 0; i < ctr; i++)
+ dput(stack[i].dentry);
+ kfree(stack);
out:
return ERR_PTR(err);
}
@@ -388,10 +444,12 @@ 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);
@@ -414,7 +472,7 @@ static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
struct path path;
int err;

- ovl_path_upper(root_dentry, &path);
+ ovl_path_real(root_dentry, &path);

err = vfs_statfs(&path, buf);
if (!err) {
@@ -436,9 +494,14 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
struct super_block *sb = dentry->d_sb;
struct ovl_fs *ufs = sb->s_fs_info;

- seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
- seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
- seq_printf(m, ",workdir=%s", ufs->config.workdir);
+ if (ufs->config.lowerdir)
+ seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
+ if (ufs->config.lowerdirs)
+ seq_printf(m, ",lowerdirs=%s", ufs->config.lowerdirs);
+ if (ufs->config.upperdir) {
+ seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+ seq_printf(m, ",workdir=%s", ufs->config.workdir);
+ }
return 0;
}

@@ -450,6 +513,7 @@ static const struct super_operations ovl_super_operations = {

enum {
OPT_LOWERDIR,
+ OPT_LOWERDIRS,
OPT_UPPERDIR,
OPT_WORKDIR,
OPT_ERR,
@@ -457,6 +521,7 @@ enum {

static const match_table_t ovl_tokens = {
{OPT_LOWERDIR, "lowerdir=%s"},
+ {OPT_LOWERDIRS, "lowerdirs=%s"},
{OPT_UPPERDIR, "upperdir=%s"},
{OPT_WORKDIR, "workdir=%s"},
{OPT_ERR, NULL}
@@ -489,6 +554,13 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
return -ENOMEM;
break;

+ case OPT_LOWERDIRS:
+ kfree(config->lowerdirs);
+ config->lowerdirs = match_strdup(&args[0]);
+ if (!config->lowerdirs)
+ return -ENOMEM;
+ break;
+
case OPT_WORKDIR:
kfree(config->workdir);
config->workdir = match_strdup(&args[0]);
@@ -554,18 +626,6 @@ out_dput:
goto out_unlock;
}

-static int ovl_mount_dir(const char *name, struct path *path)
-{
- int err;
-
- err = kern_path(name, LOOKUP_FOLLOW, path);
- if (err) {
- pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
- err = -EINVAL;
- }
- return err;
-}
-
static bool ovl_is_allowed_fs_type(struct dentry *root)
{
const struct dentry_operations *dop = root->d_op;
@@ -585,6 +645,43 @@ static bool ovl_is_allowed_fs_type(struct dentry *root)
return true;
}

+static int ovl_mount_dir(const char *name, struct path *path)
+{
+ int err;
+
+ err = kern_path(name, LOOKUP_FOLLOW, path);
+ if (err) {
+ pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
+ err = -EINVAL;
+ } else if (!ovl_is_allowed_fs_type(path->dentry)) {
+ pr_err("overlayfs: filesystem on '%s' not supported\n", name);
+ err = -EINVAL;
+ }
+
+ return err;
+}
+
+static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
+ int *stack_depth)
+{
+ int err;
+ struct kstatfs statfs;
+
+ err = ovl_mount_dir(name, path);
+ if (err)
+ return err;
+
+ err = vfs_statfs(path, &statfs);
+ if (err) {
+ pr_err("overlayfs: statfs failed on '%s'\n", name);
+ return err;
+ }
+ *namelen = max(*namelen, statfs.f_namelen);
+ *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
+
+ return err;
+}
+
/* Workdir should not be subdir of upperdir and vice versa */
static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
{
@@ -599,14 +696,15 @@ static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)

static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
- struct path lowerpath;
- struct path upperpath;
- struct path workpath;
- struct inode *root_inode;
+ struct path upperpath = { NULL, NULL };
+ struct path workpath = { NULL, NULL };
struct dentry *root_dentry;
struct ovl_entry *oe;
struct ovl_fs *ufs;
- struct kstatfs statfs;
+ struct path *stack = NULL;
+ unsigned int numlower = 0;
+ unsigned int stacklen = 0;
+ unsigned int i;
int err;

err = -ENOMEM;
@@ -618,123 +716,175 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
if (err)
goto out_free_config;

- /* FIXME: workdir is not needed for a R/O mount */
err = -EINVAL;
- if (!ufs->config.upperdir || !ufs->config.lowerdir ||
- !ufs->config.workdir) {
- pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
+ if (ufs->config.lowerdir && ufs->config.lowerdirs) {
+ pr_err("overlayfs: both 'lowerdir' and 'lowerdirs' not allowed\n");
goto out_free_config;
}
-
- err = -ENOMEM;
- oe = ovl_alloc_entry();
- if (oe == NULL)
+ if (ufs->config.upperdir && !ufs->config.workdir) {
+ pr_err("overlayfs: missing 'workdir'\n");
goto out_free_config;
-
- err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
- if (err)
- goto out_free_oe;
-
- err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
- if (err)
- goto out_put_upperpath;
-
- err = ovl_mount_dir(ufs->config.workdir, &workpath);
- if (err)
- goto out_put_lowerpath;
-
- err = -EINVAL;
- if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
- !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
- !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
- pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
- goto out_put_workpath;
- }
-
- if (upperpath.mnt != workpath.mnt) {
- pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
- goto out_put_workpath;
}
- if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
- pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
- goto out_put_workpath;
+ if (!ufs->config.upperdir &&
+ !ufs->config.lowerdir && !ufs->config.lowerdirs) {
+ pr_err("overlayfs: no 'upperdir', 'lowerdir' or 'lowerdirs' specified\n");
+ goto out_free_config;
}

- if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
- pr_err("overlayfs: filesystem of upperdir is not supported\n");
- goto out_put_workpath;
+ if (ufs->config.lowerdir) {
+ stacklen = 1;
+ } else if (ufs->config.lowerdirs) {
+ char *p = ufs->config.lowerdirs;
+
+ for (;;) {
+ stacklen++;
+ p = strchr(p, ':');
+ if (!p)
+ break;
+ p++;
+ }
}

- if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
- pr_err("overlayfs: filesystem of lowerdir is not supported\n");
- goto out_put_workpath;
+ if (stacklen) {
+ err = -ENOMEM;
+ stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
+ if (!stack)
+ goto out_free_config;
}

- err = vfs_statfs(&lowerpath, &statfs);
- if (err) {
- pr_err("overlayfs: statfs failed on lowerpath\n");
- goto out_put_workpath;
+ if (ufs->config.upperdir) {
+ err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
+ if (err)
+ goto out_free_stack;
+ err = ovl_mount_dir(ufs->config.workdir, &workpath);
+ if (err)
+ goto out_put_upperpath;
+
+ err = -EINVAL;
+ if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
+ !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
+ pr_err("overlayfs: upperdir or workdir not a directory\n");
+ goto out_put_workpath;
+ }
+ if (upperpath.mnt != workpath.mnt) {
+ pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
+ goto out_put_workpath;
+ }
+ if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
+ pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
+ goto out_put_workpath;
+ }
+ sb->s_stack_depth = max(sb->s_stack_depth,
+ upperpath.mnt->mnt_sb->s_stack_depth);
}
- ufs->lower_namelen = statfs.f_namelen;

- sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
- lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+ if (ufs->config.lowerdir) {
+ BUG_ON(numlower >= stacklen);
+
+ err = ovl_lower_dir(ufs->config.lowerdir, &stack[numlower], &ufs->lower_namelen, &sb->s_stack_depth);
+ if (err)
+ goto out_put_workpath;
+
+ numlower++;
+ } else if (ufs->config.lowerdirs) {
+ char *p = ufs->config.lowerdirs;
+
+ for (;;) {
+ char *next = strchr(p, ':');
+
+ BUG_ON(numlower >= stacklen);
+ if (next) {
+ char *str = kstrndup(p, next - p, GFP_KERNEL);
+
+ err = -ENOMEM;
+ if (!str)
+ goto out_put_lowerpath;
+
+ err = ovl_lower_dir(str, &stack[numlower], &ufs->lower_namelen, &sb->s_stack_depth);
+ if (err)
+ goto out_put_lowerpath;
+
+ numlower++;
+ kfree(str);
+ p = next + 1;
+ } else {
+ err = ovl_lower_dir(p, &stack[numlower], &ufs->lower_namelen, &sb->s_stack_depth);
+ if (err)
+ goto out_put_lowerpath;
+ numlower++;
+ break;
+ }
+ }
+ }

err = -EINVAL;
if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
pr_err("overlayfs: maximum fs stacking depth exceeded\n");
- goto out_put_workpath;
- }
-
- ufs->upper_mnt = clone_private_mount(&upperpath);
- err = PTR_ERR(ufs->upper_mnt);
- if (IS_ERR(ufs->upper_mnt)) {
- pr_err("overlayfs: failed to clone upperpath\n");
- goto out_put_workpath;
+ goto out_put_lowerpath;
}

- 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");
- goto out_put_upper_mnt;
+ if (ufs->config.upperdir) {
+ ufs->upper_mnt = clone_private_mount(&upperpath);
+ err = PTR_ERR(ufs->upper_mnt);
+ if (IS_ERR(ufs->upper_mnt)) {
+ pr_err("overlayfs: failed to clone upperpath\n");
+ goto out_put_lowerpath;
+ }
+ ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
+ err = PTR_ERR(ufs->workdir);
+ if (IS_ERR(ufs->workdir)) {
+ pr_err("overlayfs: failed to create directory %s/%s\n",
+ ufs->config.workdir, OVL_WORKDIR_NAME);
+ goto out_put_upper_mnt;
+ }
}
-
- ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
- err = PTR_ERR(ufs->workdir);
- if (IS_ERR(ufs->workdir)) {
- pr_err("overlayfs: failed to create directory %s/%s\n",
- ufs->config.workdir, OVL_WORKDIR_NAME);
- goto out_put_lower_mnt;
+ if (numlower) {
+ ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
+ if (ufs->lower_mnt == NULL)
+ goto out_put_workdir;
+ for (i = 0; i < numlower; i++) {
+ struct vfsmount *mnt = clone_private_mount(&stack[i]);
+
+ 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[ufs->numlower] = mnt;
+ ufs->numlower++;
+ }
}

- /*
- * 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)
+ if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
sb->s_flags |= MS_RDONLY;

sb->s_d_op = &ovl_dentry_operations;

err = -ENOMEM;
- root_inode = ovl_new_inode(sb, S_IFDIR, oe);
- if (!root_inode)
- goto out_put_workdir;
+ oe = ovl_alloc_entry(numlower);
+ if (!oe)
+ goto out_put_lower_mnt;

- root_dentry = d_make_root(root_inode);
+ root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
if (!root_dentry)
- goto out_put_workdir;
+ goto out_free_oe;

mntput(upperpath.mnt);
- mntput(lowerpath.mnt);
+ for (i = 0; i < numlower; i++)
+ mntput(stack[i].mnt);
path_put(&workpath);

oe->__upperdentry = upperpath.dentry;
- oe->lowerdentry = lowerpath.dentry;
+ for (i = 0; i < numlower; i++) {
+ oe->lowerstack[i].dentry = stack[i].dentry;
+ oe->lowerstack[i].mnt= ufs->lower_mnt[i];
+ }

root_dentry->d_fsdata = oe;

@@ -745,20 +895,25 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)

return 0;

+out_free_oe:
+ kfree(oe);
+out_put_lower_mnt:
+ for (i = 0; i < ufs->numlower; i++)
+ mntput(ufs->lower_mnt[i]);
+ kfree(ufs->lower_mnt);
out_put_workdir:
dput(ufs->workdir);
-out_put_lower_mnt:
- mntput(ufs->lower_mnt);
out_put_upper_mnt:
mntput(ufs->upper_mnt);
+out_put_lowerpath:
+ for (i = 0; i < numlower; i++)
+ path_put(&stack[i]);
out_put_workpath:
path_put(&workpath);
-out_put_lowerpath:
- path_put(&lowerpath);
out_put_upperpath:
path_put(&upperpath);
-out_free_oe:
- kfree(oe);
+out_free_stack:
+ kfree(stack);
out_free_config:
kfree(ufs->config.lowerdir);
kfree(ufs->config.upperdir);
--
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