ovl: make upperdir optional

Make "upperdir=" mount option optional.  If "upperdir=" is not given, then
the "workdir=" option is also optional (and ignored if given).

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 47 insertions, 36 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 592370ff453a..35bb0adf10cf 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -516,8 +516,10 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
         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.upperdir) {
+                seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+                seq_printf(m, ",workdir=%s", ufs->config.workdir);
+        }
         return 0;
 }
 
@@ -768,8 +770,8 @@ 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 path upperpath = { NULL, NULL };
+        struct path workpath = { NULL, NULL };
         struct dentry *root_dentry;
         struct ovl_entry *oe;
         struct ovl_fs *ufs;
@@ -786,31 +788,38 @@ 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) {
+                pr_err("overlayfs: missing 'lowerdir'\n");
                 goto out_free_config;
         }
 
-        err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
-        if (err)
-                goto out_free_config;
+        sb->s_stack_depth = 0;
+        if (ufs->config.upperdir) {
+                /* FIXME: workdir is not needed for a R/O mount */
+                if (!ufs->config.workdir) {
+                        pr_err("overlayfs: missing 'workdir'\n");
+                        goto out_free_config;
+                }
 
-        err = ovl_mount_dir(ufs->config.workdir, &workpath);
-        if (err)
-                goto out_put_upperpath;
+                err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
+                if (err)
+                        goto out_free_config;
 
-        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;
+                err = ovl_mount_dir(ufs->config.workdir, &workpath);
+                if (err)
+                        goto out_put_upperpath;
+
+                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 = upperpath.mnt->mnt_sb->s_stack_depth;
         }
-        sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
 
         err = ovl_lower_dir(ufs->config.lowerdir, &lowerpath,
                             &ufs->lower_namelen, &sb->s_stack_depth);
@@ -824,19 +833,21 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 goto out_put_lowerpath;
         }
 
-        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;
-        }
+        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_upper_mnt;
+                }
         }
 
         ufs->lower_mnt = kcalloc(1, sizeof(struct vfsmount *), GFP_KERNEL);
@@ -858,8 +869,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         ufs->lower_mnt[0] = mnt;
         ufs->numlower = 1;
 
-        /* If the upper fs is r/o, we mark overlayfs r/o too */
-        if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
+        /* If the upper fs is r/o or nonexistent, we mark overlayfs r/o too */
+        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;