nfsd: provide callbacks on svc_xprt deletion

NFSv4.1 needs warning when a client tcp connection goes down, if that
connection is being used as a backchannel, so that it can warn the
client that it has lost the backchannel connection.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

2 files changed, 40 insertions, 0 deletions

diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index bb182979569e..bbdb680ffbe9 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -33,6 +33,16 @@ struct svc_xprt_class {
         u32                     xcl_max_payload;
 };
 
+/*
+ * This is embedded in an object that wants a callback before deleting
+ * an xprt; intended for use by NFSv4.1, which needs to know when a
+ * client's tcp connection (and hence possibly a backchannel) goes away.
+ */
+struct svc_xpt_user {
+        struct list_head list;
+        void (*callback)(struct svc_xpt_user *);
+};
+
 struct svc_xprt {
         struct svc_xprt_class   *xpt_class;
         struct svc_xprt_ops     *xpt_ops;
@@ -67,10 +77,25 @@ struct svc_xprt {
         struct sockaddr_storage xpt_remote;     /* remote peer's address */
         size_t                  xpt_remotelen;  /* length of address */
         struct rpc_wait_queue   xpt_bc_pending; /* backchannel wait queue */
+        struct list_head        xpt_users;      /* callbacks on free */
 
         struct net              *xpt_net;
 };
 
+static inline void register_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
+{
+        spin_lock(&xpt->xpt_lock);
+        list_add(&u->list, &xpt->xpt_users);
+        spin_unlock(&xpt->xpt_lock);
+}
+
+static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
+{
+        spin_lock(&xpt->xpt_lock);
+        list_del_init(&u->list);
+        spin_unlock(&xpt->xpt_lock);
+}
+
 int     svc_reg_xprt_class(struct svc_xprt_class *);
 void    svc_unreg_xprt_class(struct svc_xprt_class *);
 void    svc_xprt_init(struct svc_xprt_class *, struct svc_xprt *,
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 678b6ee4da7b..12025eedc781 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -156,6 +156,7 @@ void svc_xprt_init(struct svc_xprt_class *xcl, struct svc_xprt *xprt,
         INIT_LIST_HEAD(&xprt->xpt_list);
         INIT_LIST_HEAD(&xprt->xpt_ready);
         INIT_LIST_HEAD(&xprt->xpt_deferred);
+        INIT_LIST_HEAD(&xprt->xpt_users);
         mutex_init(&xprt->xpt_mutex);
         spin_lock_init(&xprt->xpt_lock);
         set_bit(XPT_BUSY, &xprt->xpt_flags);
@@ -881,6 +882,19 @@ static void svc_age_temp_xprts(unsigned long closure)
         mod_timer(&serv->sv_temptimer, jiffies + svc_conn_age_period * HZ);
 }
 
+static void call_xpt_users(struct svc_xprt *xprt)
+{
+        struct svc_xpt_user *u;
+
+        spin_lock(&xprt->xpt_lock);
+        while (!list_empty(&xprt->xpt_users)) {
+                u = list_first_entry(&xprt->xpt_users, struct svc_xpt_user, list);
+                list_del(&u->list);
+                u->callback(u);
+        }
+        spin_unlock(&xprt->xpt_lock);
+}
+
 /*
  * Remove a dead transport
  */
@@ -913,6 +927,7 @@ void svc_delete_xprt(struct svc_xprt *xprt)
         while ((dr = svc_deferred_dequeue(xprt)) != NULL)
                 kfree(dr);
 
+        call_xpt_users(xprt);
         svc_xprt_put(xprt);
 }