ovl: allow redirect_dir to default to "on"

This patch introduces a kernel config option and a module param.  Both can
be used independently to turn the default value of redirect_dir on or off.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

2 files changed, 19 insertions, 0 deletions

diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index 34355818a2e0..0daac5112f7a 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -8,3 +8,17 @@ config OVERLAY_FS
           merged with the 'upper' object.
 
           For more information see Documentation/filesystems/overlayfs.txt
+
+config OVERLAY_FS_REDIRECT_DIR
+        bool "Overlayfs: turn on redirect dir feature by default"
+        depends on OVERLAY_FS
+        help
+          If this config option is enabled then overlay filesystems will use
+          redirects when renaming directories by default.  In this case it is
+          still possible to turn off redirects globally with the
+          "redirect_dir=off" module option or on a filesystem instance basis
+          with the "redirect_dir=off" mount option.
+
+          Note, that redirects are not backward compatible.  That is, mounting
+          an overlay which has redirects on a kernel that doesn't support this
+          feature will have unexpected results.
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 520f9ab0e9ef..2750aef24d16 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -28,6 +28,10 @@ struct ovl_dir_cache;
 
 #define OVL_MAX_STACK 500
 
+static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
+module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
+MODULE_PARM_DESC(ovl_redirect_dir_def,
+                 "Default to on or off for the redirect_dir feature");
 
 static void ovl_dentry_release(struct dentry *dentry)
 {
@@ -702,6 +706,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         if (!ufs)
                 goto out;
 
+        ufs->config.redirect_dir = ovl_redirect_dir_def;
         err = ovl_parse_opt((char *) data, &ufs->config);
         if (err)
                 goto out_free_config;