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 741dc0b6931fe90fc62874989c93e659f7e7a4ef..c851158324e23678b5af3f07ab10db3b8a759050 100644 (file)
--- 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 59614faa14c315fb8f6e5998f91bc7061f818bab..b2023ddb85323725b8bbfa687f31fc854c1ba5e9 100644 (file)
--- 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 6faefa54cb5ed2437c5e3c9d57f8984cdb266a48..9828b7de89992e64a1900a277b58423dde7b992a 100644 (file)
--- 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 35b8959db5ee00e455d770da3363a4a94b52f8a1..2bd4c264ccbefca9caccf9c3613149068c5d6135 100644 (file)
--- 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]);