sheepdog: try to reconnect to sheepdog after network error

This introduces a failed request queue and links all the inflight
requests to the list after network error happens.  After QEMU
reconnects to the sheepdog server successfully, the sheepdog block
driver will retry all the requests in the failed queue.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Tested-by: NLiu Yuan <namei.unix@gmail.com>
Reviewed-by: NLiu Yuan <namei.unix@gmail.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -304,6 +304,8 @@ struct SheepdogAIOCB {
 };
 
 typedef struct BDRVSheepdogState {
+    BlockDriverState *bs;
+
     SheepdogInode inode;
 
     uint32_t min_dirty_data_idx;
@@ -323,8 +325,11 @@ typedef struct BDRVSheepdogState {
     Coroutine *co_recv;
 
     uint32_t aioreq_seq_num;
+
+    /* Every aio request must be linked to either of these queues. */
     QLIST_HEAD(inflight_aio_head, AIOReq) inflight_aio_head;
     QLIST_HEAD(pending_aio_head, AIOReq) pending_aio_head;
+    QLIST_HEAD(failed_aio_head, AIOReq) failed_aio_head;
 } BDRVSheepdogState;
 
 static const char * sd_strerror(int err)
@@ -611,6 +616,8 @@ static int coroutine_fn add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
                            enum AIOCBState aiocb_type);
 static int coroutine_fn resend_aioreq(BDRVSheepdogState *s, AIOReq *aio_req);
 static int reload_inode(BDRVSheepdogState *s, uint32_t snapid, const char *tag);
+static int get_sheep_fd(BDRVSheepdogState *s);
+static void co_write_request(void *opaque);
 
 static AIOReq *find_pending_req(BDRVSheepdogState *s, uint64_t oid)
 {
@@ -652,6 +659,51 @@ static void coroutine_fn send_pending_req(BDRVSheepdogState *s, uint64_t oid)
     }
 }
 
+static coroutine_fn void reconnect_to_sdog(void *opaque)
+{
+    BDRVSheepdogState *s = opaque;
+    AIOReq *aio_req, *next;
+
+    qemu_aio_set_fd_handler(s->fd, NULL, NULL, NULL);
+    close(s->fd);
+    s->fd = -1;
+
+    /* Wait for outstanding write requests to be completed. */
+    while (s->co_send != NULL) {
+        co_write_request(opaque);
+    }
+
+    /* Try to reconnect the sheepdog server every one second. */
+    while (s->fd < 0) {
+        s->fd = get_sheep_fd(s);
+        if (s->fd < 0) {
+            DPRINTF("Wait for connection to be established\n");
+            co_aio_sleep_ns(bdrv_get_aio_context(s->bs), QEMU_CLOCK_REALTIME,
+                            1000000000ULL);
+        }
+    };
+
+    /*
+     * Now we have to resend all the request in the inflight queue.  However,
+     * resend_aioreq() can yield and newly created requests can be added to the
+     * inflight queue before the coroutine is resumed.  To avoid mixing them, we
+     * have to move all the inflight requests to the failed queue before
+     * resend_aioreq() is called.
+     */
+    QLIST_FOREACH_SAFE(aio_req, &s->inflight_aio_head, aio_siblings, next) {
+        QLIST_REMOVE(aio_req, aio_siblings);
+        QLIST_INSERT_HEAD(&s->failed_aio_head, aio_req, aio_siblings);
+    }
+
+    /* Resend all the failed aio requests. */
+    while (!QLIST_EMPTY(&s->failed_aio_head)) {
+        aio_req = QLIST_FIRST(&s->failed_aio_head);
+        QLIST_REMOVE(aio_req, aio_siblings);
+        QLIST_INSERT_HEAD(&s->inflight_aio_head, aio_req, aio_siblings);
+        resend_aioreq(s, aio_req);
+    }
+}
+
 /*
  * Receive responses of the I/O requests.
  *
@@ -668,15 +720,11 @@ static void coroutine_fn aio_read_response(void *opaque)
     SheepdogAIOCB *acb;
     uint64_t idx;
 
-    if (QLIST_EMPTY(&s->inflight_aio_head)) {
-        goto out;
-    }
-
     /* read a header */
     ret = qemu_co_recv(fd, &rsp, sizeof(rsp));
     if (ret != sizeof(rsp)) {
         error_report("failed to get the header, %s", strerror(errno));
-        goto out;
+        goto err;
     }
 
     /* find the right aio_req from the inflight aio list */
@@ -687,7 +735,7 @@ static void coroutine_fn aio_read_response(void *opaque)
     }
     if (!aio_req) {
         error_report("cannot find aio_req %x", rsp.id);
-        goto out;
+        goto err;
     }
 
     acb = aio_req->aiocb;
@@ -727,7 +775,7 @@ static void coroutine_fn aio_read_response(void *opaque)
                             aio_req->iov_offset, rsp.data_length);
         if (ret != rsp.data_length) {
             error_report("failed to get the data, %s", strerror(errno));
-            goto out;
+            goto err;
         }
         break;
     case AIOCB_FLUSH_CACHE:
@@ -761,10 +809,9 @@ static void coroutine_fn aio_read_response(void *opaque)
         if (s->inode.vdi_id == oid_to_vid(aio_req->oid)) {
             ret = reload_inode(s, 0, "");
             if (ret < 0) {
-                goto out;
+                goto err;
             }
         }
-
         if (is_data_obj(aio_req->oid)) {
             aio_req->oid = vid_to_data_oid(s->inode.vdi_id,
                                            data_oid_to_idx(aio_req->oid));
@@ -792,6 +839,10 @@ static void coroutine_fn aio_read_response(void *opaque)
     }
 out:
     s->co_recv = NULL;
+    return;
+err:
+    s->co_recv = NULL;
+    reconnect_to_sdog(opaque);
 }
 
 static void co_read_response(void *opaque)
@@ -1083,22 +1134,20 @@ static int coroutine_fn add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
     /* send a header */
     ret = qemu_co_send(s->fd, &hdr, sizeof(hdr));
     if (ret != sizeof(hdr)) {
-        qemu_co_mutex_unlock(&s->lock);
         error_report("failed to send a req, %s", strerror(errno));
-        return -errno;
+        goto out;
     }
 
     if (wlen) {
         ret = qemu_co_sendv(s->fd, iov, niov, aio_req->iov_offset, wlen);
         if (ret != wlen) {
-            qemu_co_mutex_unlock(&s->lock);
             error_report("failed to send a data, %s", strerror(errno));
-            return -errno;
         }
     }
-
+out:
     socket_set_cork(s->fd, 0);
     qemu_aio_set_fd_handler(s->fd, co_read_response, NULL, s);
+    s->co_send = NULL;
     qemu_co_mutex_unlock(&s->lock);
 
     return 0;
@@ -1276,6 +1325,8 @@ static int sd_open(BlockDriverState *bs, QDict *options, int flags,
     Error *local_err = NULL;
     const char *filename;
 
+    s->bs = bs;
+
     opts = qemu_opts_create_nofail(&runtime_opts);
     qemu_opts_absorb_qdict(opts, options, &local_err);
     if (error_is_set(&local_err)) {
@@ -1289,6 +1340,7 @@ static int sd_open(BlockDriverState *bs, QDict *options, int flags,
 
     QLIST_INIT(&s->inflight_aio_head);
     QLIST_INIT(&s->pending_aio_head);
+    QLIST_INIT(&s->failed_aio_head);
     s->fd = -1;
 
     memset(vdi, 0, sizeof(vdi));