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);
Indeed, Miklos, changing layers dynamically is VERY tricky. Unionfs supports that, but a good amount of its code all over is dedicated to handling dynamic layer changes. I advise you to avoid supporting this feature for a while, if ever: get a small, functional, working overlayfs first.
I personally never liked the idea of changing layers dynamically: it’s like asking a file system to remain consistent and detect all lower changes when someone goes and hand-edits disk blocks. Too messy. The pain of developing and supporting such a feature is much greater than the annoyance to users who have to unmount and remount back their layers to form a new structure.
Cheers,
Erez.
> On Nov 10, 2014, at 4:09 AM, Miklos Szeredi <[email protected]> wrote:
>
> 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
EL Mon, 10 Nov 2014 10:09:54 +0100
Miklos Szeredi <[email protected]> escrigué:
> Maybe it wasn't clear, but the number of lower layers isn't limited by
> FILESYSTEM_MAX_STACK_DEPTH,
sorry, you have been clear, it's me that have not explained the purpose
of that patch. This idea is also valid for the main overlayfs
development.
Consider that we have an encrypted partition and a live OS that
uses overlayfs and works over it, when the OS is started already
reaches the maximum stacking depth (2). Also, hardcoding parameters
into the code may be annoying because a change implies creating and
mantaining patches, otherwise when the parameter is configurable we can
change it in a config value.
Also, I include a patch to explain better my first statement,
would say lowerdirs has extended the functionality of lowerdir,
therefore we can discard the lowerdir case that only works with one
lower layer and rename lowerdirs to lowerdir. It's more simple and all
the functionality is preserved.
Regards,
Jordi Pujol
On Fri, Nov 14, 2014 at 9:55 AM, Jordi Pujol Palomer
<[email protected]> wrote:
> EL Mon, 10 Nov 2014 10:09:54 +0100
> Miklos Szeredi <[email protected]> escrigué:
>
>> Maybe it wasn't clear, but the number of lower layers isn't limited by
>> FILESYSTEM_MAX_STACK_DEPTH,
> sorry, you have been clear, it's me that have not explained the purpose
> of that patch. This idea is also valid for the main overlayfs
> development.
> Consider that we have an encrypted partition and a live OS that
> uses overlayfs and works over it, when the OS is started already
> reaches the maximum stacking depth (2). Also, hardcoding parameters
> into the code may be annoying because a change implies creating and
> mantaining patches, otherwise when the parameter is configurable we can
> change it in a config value.
Before allowing a change to FILESYSTEM_MAX_STACK_DEPTH we'd need to
analyze the kernel stack usage of anything taking part in the
filesystem stack. Not something that can be expected of users before
they set a kernel config variable.
'Course we can change overlayfs and/or ecryptfs to use a new context
for operations done on underlying layers. Not sure how much work that
would be...
> Also, I include a patch to explain better my first statement,
> would say lowerdirs has extended the functionality of lowerdir,
> therefore we can discard the lowerdir case that only works with one
> lower layer and rename lowerdirs to lowerdir. It's more simple and all
> the functionality is preserved.
Yeah. But we also need some escaping in 'lowerdir=' argument to allow
filenames with comma and colon. Current patch doesn't yet have that,
but will work on it.
Thanks,
Miklos