sheepdog: use coroutines

This makes the sheepdog block driver support bdrv_co_readv/writev
instead of bdrv_aio_readv/writev.

With this patch, Sheepdog network I/O becomes fully asynchronous.  The
block driver yields back when send/recv returns EAGAIN, and is resumed
when the sheepdog network connection is ready for the operation.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -274,7 +274,7 @@ struct SheepdogAIOCB {
     int ret;
     enum AIOCBState aiocb_type;
 
-    QEMUBH *bh;
+    Coroutine *coroutine;
     void (*aio_done_func)(SheepdogAIOCB *);
 
     int canceled;
@@ -295,6 +295,10 @@ typedef struct BDRVSheepdogState {
     char *port;
     int fd;
 
+    CoMutex lock;
+    Coroutine *co_send;
+    Coroutine *co_recv;
+
     uint32_t aioreq_seq_num;
     QLIST_HEAD(outstanding_aio_head, AIOReq) outstanding_aio_head;
 } BDRVSheepdogState;
@@ -346,19 +350,16 @@ static const char * sd_strerror(int err)
 /*
  * Sheepdog I/O handling:
  *
- * 1. In the sd_aio_readv/writev, read/write requests are added to the
+ * 1. In sd_co_rw_vector, we send the I/O requests to the server and
- *    QEMU Bottom Halves.
+ *    link the requests to the outstanding_list in the
+ *    BDRVSheepdogState.  The function exits without waiting for
+ *    receiving the response.
  *
- * 2. In sd_readv_writev_bh_cb, the callbacks of BHs, we send the I/O
+ * 2. We receive the response in aio_read_response, the fd handler to
- *    requests to the server and link the requests to the
- *    outstanding_list in the BDRVSheepdogState.  we exits the
- *    function without waiting for receiving the response.
- *
- * 3. We receive the response in aio_read_response, the fd handler to
  *    the sheepdog connection.  If metadata update is needed, we send
  *    the write request to the vdi object in sd_write_done, the write
- *    completion function.  The AIOCB callback is not called until all
+ *    completion function.  We switch back to sd_co_readv/writev after
- *    the requests belonging to the AIOCB are finished.
+ *    all the requests belonging to the AIOCB are finished.
  */
 
 static inline AIOReq *alloc_aio_req(BDRVSheepdogState *s, SheepdogAIOCB *acb,
@@ -398,7 +399,7 @@ static inline int free_aio_req(BDRVSheepdogState *s, AIOReq *aio_req)
 static void sd_finish_aiocb(SheepdogAIOCB *acb)
 {
     if (!acb->canceled) {
-        acb->common.cb(acb->common.opaque, acb->ret);
+        qemu_coroutine_enter(acb->coroutine, NULL);
     }
     qemu_aio_release(acb);
 }
@@ -411,7 +412,8 @@ static void sd_aio_cancel(BlockDriverAIOCB *blockacb)
      * Sheepdog cannot cancel the requests which are already sent to
      * the servers, so we just complete the request with -EIO here.
      */
-    acb->common.cb(acb->common.opaque, -EIO);
+    acb->ret = -EIO;
+    qemu_coroutine_enter(acb->coroutine, NULL);
     acb->canceled = 1;
 }
 
@@ -435,24 +437,12 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
 
     acb->aio_done_func = NULL;
     acb->canceled = 0;
-    acb->bh = NULL;
+    acb->coroutine = qemu_coroutine_self();
     acb->ret = 0;
     QLIST_INIT(&acb->aioreq_head);
     return acb;
 }
 
-static int sd_schedule_bh(QEMUBHFunc *cb, SheepdogAIOCB *acb)
-{
-    if (acb->bh) {
-        error_report("bug: %d %d", acb->aiocb_type, acb->aiocb_type);
-        return -EIO;
-    }
-
-    acb->bh = qemu_bh_new(cb, acb);
-    qemu_bh_schedule(acb->bh);
-    return 0;
-}
-
 #ifdef _WIN32
 
 struct msghdr {
@@ -635,7 +625,13 @@ static int do_readv_writev(int sockfd, struct iovec *iov, int len,
 again:
     ret = do_send_recv(sockfd, iov, len, iov_offset, write);
     if (ret < 0) {
-        if (errno == EINTR || errno == EAGAIN) {
+        if (errno == EINTR) {
+            goto again;
+        }
+        if (errno == EAGAIN) {
+            if (qemu_in_coroutine()) {
+                qemu_coroutine_yield();
+            }
             goto again;
         }
         error_report("failed to recv a rsp, %s", strerror(errno));
@@ -793,14 +789,14 @@ static void aio_read_response(void *opaque)
     unsigned long idx;
 
     if (QLIST_EMPTY(&s->outstanding_aio_head)) {
-        return;
+        goto out;
     }
 
     /* read a header */
     ret = do_read(fd, &rsp, sizeof(rsp));
     if (ret) {
         error_report("failed to get the header, %s", strerror(errno));
-        return;
+        goto out;
     }
 
     /* find the right aio_req from the outstanding_aio list */
@@ -811,7 +807,7 @@ static void aio_read_response(void *opaque)
     }
     if (!aio_req) {
         error_report("cannot find aio_req %x", rsp.id);
-        return;
+        goto out;
     }
 
     acb = aio_req->aiocb;
@@ -847,7 +843,7 @@ static void aio_read_response(void *opaque)
                        aio_req->iov_offset);
         if (ret) {
             error_report("failed to get the data, %s", strerror(errno));
-            return;
+            goto out;
         }
         break;
     }
@@ -861,10 +857,30 @@ static void aio_read_response(void *opaque)
     if (!rest) {
         /*
          * We've finished all requests which belong to the AIOCB, so
-         * we can call the callback now.
+         * we can switch back to sd_co_readv/writev now.
          */
         acb->aio_done_func(acb);
     }
+out:
+    s->co_recv = NULL;
+}
+
+static void co_read_response(void *opaque)
+{
+    BDRVSheepdogState *s = opaque;
+
+    if (!s->co_recv) {
+        s->co_recv = qemu_coroutine_create(aio_read_response);
+    }
+
+    qemu_coroutine_enter(s->co_recv, opaque);
+}
+
+static void co_write_request(void *opaque)
+{
+    BDRVSheepdogState *s = opaque;
+
+    qemu_coroutine_enter(s->co_send, NULL);
 }
 
 static int aio_flush_request(void *opaque)
@@ -924,7 +940,7 @@ static int get_sheep_fd(BDRVSheepdogState *s)
         return -1;
     }
 
-    qemu_aio_set_fd_handler(fd, aio_read_response, NULL, aio_flush_request,
+    qemu_aio_set_fd_handler(fd, co_read_response, NULL, aio_flush_request,
                             NULL, s);
     return fd;
 }
@@ -1091,6 +1107,10 @@ static int add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
 
     hdr.id = aio_req->id;
 
+    qemu_co_mutex_lock(&s->lock);
+    s->co_send = qemu_coroutine_self();
+    qemu_aio_set_fd_handler(s->fd, co_read_response, co_write_request,
+                            aio_flush_request, NULL, s);
     set_cork(s->fd, 1);
 
     /* send a header */
@@ -1109,6 +1129,9 @@ static int add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
     }
 
     set_cork(s->fd, 0);
+    qemu_aio_set_fd_handler(s->fd, co_read_response, NULL,
+                            aio_flush_request, NULL, s);
+    qemu_co_mutex_unlock(&s->lock);
 
     return 0;
 }
@@ -1225,6 +1248,7 @@ static int sd_open(BlockDriverState *bs, const char *filename, int flags)
 
     bs->total_sectors = s->inode.vdi_size / SECTOR_SIZE;
     strncpy(s->name, vdi, sizeof(s->name));
+    qemu_co_mutex_init(&s->lock);
     g_free(buf);
     return 0;
 out:
@@ -1491,7 +1515,7 @@ static int sd_truncate(BlockDriverState *bs, int64_t offset)
 /*
  * This function is called after writing data objects.  If we need to
  * update metadata, this sends a write request to the vdi object.
- * Otherwise, this calls the AIOCB callback.
+ * Otherwise, this switches back to sd_co_readv/writev.
  */
 static void sd_write_done(SheepdogAIOCB *acb)
 {
@@ -1587,8 +1611,11 @@ out:
  * waiting the response.  The responses are received in the
  * `aio_read_response' function which is called from the main loop as
  * a fd handler.
+ *
+ * Returns 1 when we need to wait a response, 0 when there is no sent
+ * request and -errno in error cases.
  */
-static void sd_readv_writev_bh_cb(void *p)
+static int sd_co_rw_vector(void *p)
 {
     SheepdogAIOCB *acb = p;
     int ret = 0;
@@ -1600,9 +1627,6 @@ static void sd_readv_writev_bh_cb(void *p)
     SheepdogInode *inode = &s->inode;
     AIOReq *aio_req;
 
-    qemu_bh_delete(acb->bh);
-    acb->bh = NULL;
-
     if (acb->aiocb_type == AIOCB_WRITE_UDATA && s->is_snapshot) {
         /*
          * In the case we open the snapshot VDI, Sheepdog creates the
@@ -1684,42 +1708,47 @@ static void sd_readv_writev_bh_cb(void *p)
     }
 out:
     if (QLIST_EMPTY(&acb->aioreq_head)) {
-        sd_finish_aiocb(acb);
+        return acb->ret;
     }
+    return 1;
 }
 
-static BlockDriverAIOCB *sd_aio_writev(BlockDriverState *bs, int64_t sector_num,
+static int sd_co_writev(BlockDriverState *bs, int64_t sector_num,
-                                       QEMUIOVector *qiov, int nb_sectors,
+                        int nb_sectors, QEMUIOVector *qiov)
-                                       BlockDriverCompletionFunc *cb,
-                                       void *opaque)
 {
     SheepdogAIOCB *acb;
+    int ret;
 
     if (bs->growable && sector_num + nb_sectors > bs->total_sectors) {
         /* TODO: shouldn't block here */
         if (sd_truncate(bs, (sector_num + nb_sectors) * SECTOR_SIZE) < 0) {
-            return NULL;
+            return -EIO;
         }
         bs->total_sectors = sector_num + nb_sectors;
     }
 
-    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, cb, opaque);
+    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, NULL, NULL);
     acb->aio_done_func = sd_write_done;
     acb->aiocb_type = AIOCB_WRITE_UDATA;
 
-    sd_schedule_bh(sd_readv_writev_bh_cb, acb);
+    ret = sd_co_rw_vector(acb);
-    return &acb->common;
+    if (ret <= 0) {
+        qemu_aio_release(acb);
+        return ret;
+    }
+
+    qemu_coroutine_yield();
+
+    return acb->ret;
 }
 
-static BlockDriverAIOCB *sd_aio_readv(BlockDriverState *bs, int64_t sector_num,
+static int sd_co_readv(BlockDriverState *bs, int64_t sector_num,
-                                      QEMUIOVector *qiov, int nb_sectors,
+                       int nb_sectors, QEMUIOVector *qiov)
-                                      BlockDriverCompletionFunc *cb,
-                                      void *opaque)
 {
     SheepdogAIOCB *acb;
-    int i;
+    int i, ret;
 
-    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, cb, opaque);
+    acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors, NULL, NULL);
     acb->aiocb_type = AIOCB_READ_UDATA;
     acb->aio_done_func = sd_finish_aiocb;
 
@@ -1731,8 +1760,15 @@ static BlockDriverAIOCB *sd_aio_readv(BlockDriverState *bs, int64_t sector_num,
         memset(qiov->iov[i].iov_base, 0, qiov->iov[i].iov_len);
     }
 
-    sd_schedule_bh(sd_readv_writev_bh_cb, acb);
+    ret = sd_co_rw_vector(acb);
-    return &acb->common;
+    if (ret <= 0) {
+        qemu_aio_release(acb);
+        return ret;
+    }
+
+    qemu_coroutine_yield();
+
+    return acb->ret;
 }
 
 static int sd_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info)
@@ -2062,8 +2098,8 @@ BlockDriver bdrv_sheepdog = {
     .bdrv_getlength = sd_getlength,
     .bdrv_truncate  = sd_truncate,
 
-    .bdrv_aio_readv     = sd_aio_readv,
+    .bdrv_co_readv  = sd_co_readv,
-    .bdrv_aio_writev    = sd_aio_writev,
+    .bdrv_co_writev = sd_co_writev,
 
     .bdrv_snapshot_create   = sd_snapshot_create,
     .bdrv_snapshot_goto     = sd_snapshot_goto,