hyperv/vmbus: Add supportive transaction wait function.

[sepherosa_gmail.com]

Summary

This function supports channel revocation properly.

head/sys/dev/hyperv/include/vmbus.h

 struct vmbus_chan_br {
         void            *cbr;
         bus_addr_t      cbr_paddr;
         int             cbr_txsz;
         int             cbr_rxsz;
 };
 
 struct vmbus_channel;
+struct vmbus_xact;
 struct vmbus_xact_ctx;
 struct hyperv_guid;
 struct task;
 struct taskqueue;
 
 typedef void        (*vmbus_chan_callback_t)(struct vmbus_channel *, void *);
 
 static __inline struct vmbus_channel *

 void                vmbus_chan_close(struct vmbus_channel *chan);
 int                vmbus_chan_close_direct(struct vmbus_channel *chan);
 void                vmbus_chan_intr_drain(struct vmbus_channel *chan);
 void                vmbus_chan_run_task(struct vmbus_channel *chan,
                     struct task *task);
 void                vmbus_chan_set_orphan(struct vmbus_channel *chan,
                     struct vmbus_xact_ctx *);
 void                vmbus_chan_unset_orphan(struct vmbus_channel *chan);
+const void        *vmbus_chan_xact_wait(const struct vmbus_channel *chan,
+                    struct vmbus_xact *xact, size_t *resp_len, bool can_sleep);
 
 int                vmbus_chan_gpadl_connect(struct vmbus_channel *chan,
                     bus_addr_t paddr, int size, uint32_t *gpadl);
 int                vmbus_chan_gpadl_disconnect(struct vmbus_channel *chan,
                     uint32_t gpadl);
 
 void                vmbus_chan_cpu_set(struct vmbus_channel *chan, int cpu);
 void                vmbus_chan_cpu_rr(struct vmbus_channel *chan);

head/sys/dev/hyperv/vmbus/vmbus_chan.c

 void
 vmbus_chan_unset_orphan(struct vmbus_channel *chan)
 {
 
         sx_xlock(&chan->ch_orphan_lock);
         chan->ch_orphan_xact = NULL;
         sx_xunlock(&chan->ch_orphan_lock);
 }
+
+const void *
+vmbus_chan_xact_wait(const struct vmbus_channel *chan,
+    struct vmbus_xact *xact, size_t *resp_len, bool can_sleep)
+{
+        const void *ret;
+
+        if (can_sleep)
+                ret = vmbus_xact_wait(xact, resp_len);
+        else
+                ret = vmbus_xact_busywait(xact, resp_len);
+        if (vmbus_chan_is_revoked(chan)) {
+                /*
+                 * This xact probably is interrupted, and the
+                 * interruption can race the reply reception,
+                 * so we have to make sure that there are nothing
+                 * left on the RX bufring, i.e. this xact will
+                 * not be touched, once this function returns.
+                 *
+                 * Since the hypervisor will not put more data
+                 * onto the RX bufring once the channel is revoked,
+                 * the following loop will be terminated, once all
+                 * data are drained by the driver's channel
+                 * callback.
+                 */
+                while (!vmbus_chan_rx_empty(chan)) {
+                        if (can_sleep)
+                                pause("chxact", 1);
+                        else
+                                DELAY(1000);
+                }
+        }
+        return (ret);
+}