1 files changed, 38 insertions, 2 deletions

diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index c49502329ab0..52c426665154 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -89,7 +89,8 @@
 #define OCFS2_FEATURE_INCOMPAT_SUPP     (OCFS2_FEATURE_INCOMPAT_LOCAL_MOUNT \
                                          | OCFS2_FEATURE_INCOMPAT_SPARSE_ALLOC \
                                          | OCFS2_FEATURE_INCOMPAT_INLINE_DATA \
-                                         | OCFS2_FEATURE_INCOMPAT_EXTENDED_SLOT_MAP)
+                                         | OCFS2_FEATURE_INCOMPAT_EXTENDED_SLOT_MAP \
+                                         | OCFS2_FEATURE_INCOMPAT_USERSPACE_STACK)
 #define OCFS2_FEATURE_RO_COMPAT_SUPP    OCFS2_FEATURE_RO_COMPAT_UNWRITTEN
 
 /*
@@ -131,6 +132,17 @@
 
 
 /*
+ * Support for alternate, userspace cluster stacks.  If set, the superblock
+ * field s_cluster_info contains a tag for the alternate stack in use as
+ * well as the name of the cluster being joined.
+ * mount.ocfs2 must pass in a matching stack name.
+ *
+ * If not set, the classic stack will be used.  This is compatbile with
+ * all older versions.
+ */
+#define OCFS2_FEATURE_INCOMPAT_USERSPACE_STACK  0x0080
+
+/*
  * backup superblock flag is used to indicate that this volume
  * has backup superblocks.
  */
@@ -272,6 +284,10 @@ struct ocfs2_new_group_input {
 #define OCFS2_VOL_UUID_LEN              16
 #define OCFS2_MAX_VOL_LABEL_LEN         64
 
+/* The alternate, userspace stack fields */
+#define OCFS2_STACK_LABEL_LEN           4
+#define OCFS2_CLUSTER_NAME_LEN          16
+
 /* Journal limits (in bytes) */
 #define OCFS2_MIN_JOURNAL_SIZE          (4 * 1024 * 1024)
 
@@ -513,6 +529,13 @@ struct ocfs2_slot_map_extended {
  */
 };
 
+struct ocfs2_cluster_info {
+/*00*/  __u8   ci_stack[OCFS2_STACK_LABEL_LEN];
+        __le32 ci_reserved;
+/*08*/  __u8   ci_cluster[OCFS2_CLUSTER_NAME_LEN];
+/*18*/
+};
+
 /*
  * On disk superblock for OCFS2
  * Note that it is contained inside an ocfs2_dinode, so all offsets
@@ -545,7 +568,20 @@ struct ocfs2_super_block {
                                          * group header */
 /*50*/  __u8  s_label[OCFS2_MAX_VOL_LABEL_LEN]; /* Label for mounting, etc. */
 /*90*/  __u8  s_uuid[OCFS2_VOL_UUID_LEN];       /* 128-bit uuid */
-/*A0*/
+/*A0*/  struct ocfs2_cluster_info s_cluster_info; /* Selected userspace
+                                                     stack.  Only valid
+                                                     with INCOMPAT flag. */
+/*B8*/  __le64 s_reserved2[17];         /* Fill out superblock */
+/*140*/
+
+        /*
+         * NOTE: As stated above, all offsets are relative to
+         * ocfs2_dinode.id2, which is at 0xC0 in the inode.
+         * 0xC0 + 0x140 = 0x200 or 512 bytes.  A superblock must fit within
+         * our smallest blocksize, which is 512 bytes.  To ensure this,
+         * we reserve the space in s_reserved2.  Anything past s_reserved2
+         * will not be available on the smallest blocksize.
+         */
 };
 
 /*