+#ifdef HAVE_AUTOMOUNT
+static struct vfsmount *
+zpl_snapdir_automount(struct path *path)
+{
+ struct dentry *dentry = path->dentry;
+ int error;
+
+ /*
+ * We must briefly disable automounts for this dentry because the
+ * user space mount utility will trigger another lookup on this
+ * directory. That will result in zpl_snapdir_automount() being
+ * called repeatedly. The DCACHE_NEED_AUTOMOUNT flag can be
+ * safely reset once the mount completes.
+ */
+ dentry->d_flags &= ~DCACHE_NEED_AUTOMOUNT;
+ error = -zfsctl_mount_snapshot(path, 0);
+ dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
+ if (error)
+ return ERR_PTR(error);
+
+ /*
+ * Rather than returning the new vfsmount for the snapshot we must
+ * return NULL to indicate a mount collision. This is done because
+ * the user space mount calls do_add_mount() which adds the vfsmount
+ * to the name space. If we returned the new mount here it would be
+ * added again to the vfsmount list resulting in list corruption.
+ */
+ return (NULL);
+}
+#endif /* HAVE_AUTOMOUNT */
+
+/*
+ * Revalidate any dentry in the snapshot directory on lookup, since a snapshot
+ * having the same name have been created or destroyed since it was cached.
+ */
+static int
+#ifdef HAVE_D_REVALIDATE_NAMEIDATA
+zpl_snapdir_revalidate(struct dentry *dentry, struct nameidata *i)
+#else
+zpl_snapdir_revalidate(struct dentry *dentry, unsigned int flags)
+#endif
+{
+ return 0;
+}
+
+dentry_operations_t zpl_dops_snapdirs = {
+/*
+ * Auto mounting of snapshots is only supported for 2.6.37 and
+ * newer kernels. Prior to this kernel the ops->follow_link()
+ * callback was used as a hack to trigger the mount. The
+ * resulting vfsmount was then explicitly grafted in to the
+ * name space. While it might be possible to add compatibility
+ * code to accomplish this it would require considerable care.
+ */
+#ifdef HAVE_AUTOMOUNT
+ .d_automount = zpl_snapdir_automount,
+#endif /* HAVE_AUTOMOUNT */
+ .d_revalidate = zpl_snapdir_revalidate,
+};
+