1 files changed, 36 insertions, 0 deletions

diff --git a/fs/ocfs2/dlm/dlmfs.c b/fs/ocfs2/dlm/dlmfs.c
index 02bf17808bdc..77d0df42fe02 100644
--- a/fs/ocfs2/dlm/dlmfs.c
+++ b/fs/ocfs2/dlm/dlmfs.c
@@ -81,6 +81,42 @@ static const struct dlm_protocol_version user_locking_protocol = {
         .pv_minor = OCFS2_LOCKING_PROTOCOL_MINOR,
 };
 
+
+/*
+ * These are the ABI capabilities of dlmfs.
+ *
+ * Over time, dlmfs has added some features that were not part of the
+ * initial ABI.  Unfortunately, some of these features are not detectable
+ * via standard usage.  For example, Linux's default poll always returns
+ * POLLIN, so there is no way for a caller of poll(2) to know when dlmfs
+ * added poll support.  Instead, we provide this list of new capabilities.
+ *
+ * Capabilities is a read-only attribute.  We do it as a module parameter
+ * so we can discover it whether dlmfs is built in, loaded, or even not
+ * loaded.
+ *
+ * The ABI features are local to this machine's dlmfs mount.  This is
+ * distinct from the locking protocol, which is concerned with inter-node
+ * interaction.
+ */
+#define DLMFS_CAPABILITIES ""
+extern int param_set_dlmfs_capabilities(const char *val,
+                                        struct kernel_param *kp)
+{
+        printk(KERN_ERR "%s: readonly parameter\n", kp->name);
+        return -EINVAL;
+}
+static int param_get_dlmfs_capabilities(char *buffer,
+                                        struct kernel_param *kp)
+{
+        return strlcpy(buffer, DLMFS_CAPABILITIES,
+                       strlen(DLMFS_CAPABILITIES) + 1);
+}
+module_param_call(capabilities, param_set_dlmfs_capabilities,
+                  param_get_dlmfs_capabilities, NULL, 0444);
+MODULE_PARM_DESC(capabilities, DLMFS_CAPABILITIES);
+
+
 /*
  * decodes a set of open flags into a valid lock level and a set of flags.
  * returns < 0 if we have invalid flags