ovl: check if all layers are on the same fs
Some features can only work when all layers are on the same fs. Test this
condition during mount time, so features can check them later.
Add helper ovl_same_sb() to return the common super block in case all
layers are on the same fs.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 741dc0b..c851158 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -151,6 +151,7 @@ int ovl_want_write(struct dentry *dentry);
void ovl_drop_write(struct dentry *dentry);
struct dentry *ovl_workdir(struct dentry *dentry);
const struct cred *ovl_override_creds(struct super_block *sb);
+struct super_block *ovl_same_sb(struct super_block *sb);
struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
bool ovl_dentry_remote(struct dentry *dentry);
bool ovl_dentry_weird(struct dentry *dentry);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 59614fa..b2023ddb 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -29,6 +29,8 @@ struct ovl_fs {
const struct cred *creator_cred;
bool tmpfile;
wait_queue_head_t copyup_wq;
+ /* sb common to all layers */
+ struct super_block *same_sb;
};
/* private information held for every overlayfs dentry */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 6faefa54..9828b7d 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -914,11 +914,19 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
ufs->lower_mnt[ufs->numlower] = mnt;
ufs->numlower++;
+
+ /* Check if all lower layers are on same sb */
+ if (i == 0)
+ ufs->same_sb = mnt->mnt_sb;
+ else if (ufs->same_sb != mnt->mnt_sb)
+ ufs->same_sb = NULL;
}
/* If the upper fs is nonexistent, we mark overlayfs r/o too */
if (!ufs->upper_mnt)
sb->s_flags |= MS_RDONLY;
+ else if (ufs->upper_mnt->mnt_sb != ufs->same_sb)
+ ufs->same_sb = NULL;
if (remote)
sb->s_d_op = &ovl_reval_dentry_operations;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 35b8959d..2bd4c26 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -41,6 +41,13 @@ const struct cred *ovl_override_creds(struct super_block *sb)
return override_creds(ofs->creator_cred);
}
+struct super_block *ovl_same_sb(struct super_block *sb)
+{
+ struct ovl_fs *ofs = sb->s_fs_info;
+
+ return ofs->same_sb;
+}
+
struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
{
size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);