qemu

virtio-blk.c (10461B)

---

 /*
  * Dedicated thread for virtio-blk I/O processing
  *
  * Copyright 2012 IBM, Corp.
  * Copyright 2012 Red Hat, Inc. and/or its affiliates
  *
  * Authors:
  *   Stefan Hajnoczi <stefanha@redhat.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  * See the COPYING file in the top-level directory.
  *
  */
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "trace.h"
 #include "qemu/iov.h"
 #include "qemu/main-loop.h"
 #include "qemu/thread.h"
 #include "qemu/error-report.h"
 #include "hw/virtio/virtio-access.h"
 #include "hw/virtio/virtio-blk.h"
 #include "virtio-blk.h"
 #include "block/aio.h"
 #include "hw/virtio/virtio-bus.h"
 #include "qom/object_interfaces.h"
 
 struct VirtIOBlockDataPlane {
     bool starting;
     bool stopping;
 
     VirtIOBlkConf *conf;
     VirtIODevice *vdev;
     QEMUBH *bh;                     /* bh for guest notification */
     unsigned long *batch_notify_vqs;
     bool batch_notifications;
 
     /* Note that these EventNotifiers are assigned by value.  This is
      * fine as long as you do not call event_notifier_cleanup on them
      * (because you don't own the file descriptor or handle; you just
      * use it).
      */
     IOThread *iothread;
     AioContext *ctx;
 };
 
 /* Raise an interrupt to signal guest, if necessary */
 void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s, VirtQueue *vq)
 {
     if (s->batch_notifications) {
         set_bit(virtio_get_queue_index(vq), s->batch_notify_vqs);
         qemu_bh_schedule(s->bh);
     } else {
         virtio_notify_irqfd(s->vdev, vq);
     }
 }
 
 static void notify_guest_bh(void *opaque)
 {
     VirtIOBlockDataPlane *s = opaque;
     unsigned nvqs = s->conf->num_queues;
     unsigned long bitmap[BITS_TO_LONGS(nvqs)];
     unsigned j;
 
     memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap));
     memset(s->batch_notify_vqs, 0, sizeof(bitmap));
 
     for (j = 0; j < nvqs; j += BITS_PER_LONG) {
         unsigned long bits = bitmap[j / BITS_PER_LONG];
 
         while (bits != 0) {
             unsigned i = j + ctzl(bits);
             VirtQueue *vq = virtio_get_queue(s->vdev, i);
 
             virtio_notify_irqfd(s->vdev, vq);
 
             bits &= bits - 1; /* clear right-most bit */
         }
     }
 }
 
 /* Context: QEMU global mutex held */
 bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
                                   VirtIOBlockDataPlane **dataplane,
                                   Error **errp)
 {
     VirtIOBlockDataPlane *s;
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 
     *dataplane = NULL;
 
     if (conf->iothread) {
         if (!k->set_guest_notifiers || !k->ioeventfd_assign) {
             error_setg(errp,
                        "device is incompatible with iothread "
                        "(transport does not support notifiers)");
             return false;
         }
         if (!virtio_device_ioeventfd_enabled(vdev)) {
             error_setg(errp, "ioeventfd is required for iothread");
             return false;
         }
 
         /* If dataplane is (re-)enabled while the guest is running there could
          * be block jobs that can conflict.
          */
         if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
             error_prepend(errp, "cannot start virtio-blk dataplane: ");
             return false;
         }
     }
     /* Don't try if transport does not support notifiers. */
     if (!virtio_device_ioeventfd_enabled(vdev)) {
         return false;
     }
 
     s = g_new0(VirtIOBlockDataPlane, 1);
     s->vdev = vdev;
     s->conf = conf;
 
     if (conf->iothread) {
         s->iothread = conf->iothread;
         object_ref(OBJECT(s->iothread));
         s->ctx = iothread_get_aio_context(s->iothread);
     } else {
         s->ctx = qemu_get_aio_context();
     }
     s->bh = aio_bh_new(s->ctx, notify_guest_bh, s);
     s->batch_notify_vqs = bitmap_new(conf->num_queues);
 
     *dataplane = s;
 
     return true;
 }
 
 /* Context: QEMU global mutex held */
 void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
 {
     VirtIOBlock *vblk;
 
     if (!s) {
         return;
     }
 
     vblk = VIRTIO_BLK(s->vdev);
     assert(!vblk->dataplane_started);
     g_free(s->batch_notify_vqs);
     qemu_bh_delete(s->bh);
     if (s->iothread) {
         object_unref(OBJECT(s->iothread));
     }
     g_free(s);
 }
 
 /* Context: QEMU global mutex held */
 int virtio_blk_data_plane_start(VirtIODevice *vdev)
 {
     VirtIOBlock *vblk = VIRTIO_BLK(vdev);
     VirtIOBlockDataPlane *s = vblk->dataplane;
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vblk)));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
     AioContext *old_context;
     unsigned i;
     unsigned nvqs = s->conf->num_queues;
     Error *local_err = NULL;
     int r;
 
     if (vblk->dataplane_started || s->starting) {
         return 0;
     }
 
     s->starting = true;
 
     if (!virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
         s->batch_notifications = true;
     } else {
         s->batch_notifications = false;
     }
 
     /* Set up guest notifier (irq) */
     r = k->set_guest_notifiers(qbus->parent, nvqs, true);
     if (r != 0) {
         error_report("virtio-blk failed to set guest notifier (%d), "
                      "ensure -accel kvm is set.", r);
         goto fail_guest_notifiers;
     }
 
     /*
      * Batch all the host notifiers in a single transaction to avoid
      * quadratic time complexity in address_space_update_ioeventfds().
      */
     memory_region_transaction_begin();
 
     /* Set up virtqueue notify */
     for (i = 0; i < nvqs; i++) {
         r = virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, true);
         if (r != 0) {
             int j = i;
 
             fprintf(stderr, "virtio-blk failed to set host notifier (%d)\n", r);
             while (i--) {
                 virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
             }
 
             /*
              * The transaction expects the ioeventfds to be open when it
              * commits. Do it now, before the cleanup loop.
              */
             memory_region_transaction_commit();
 
             while (j--) {
                 virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), j);
             }
             goto fail_host_notifiers;
         }
     }
 
     memory_region_transaction_commit();
 
     /*
      * These fields are visible to the IOThread so we rely on implicit barriers
      * in aio_context_acquire() on the write side and aio_notify_accept() on
      * the read side.
      */
     s->starting = false;
     vblk->dataplane_started = true;
     trace_virtio_blk_data_plane_start(s);
 
     old_context = blk_get_aio_context(s->conf->conf.blk);
     aio_context_acquire(old_context);
     r = blk_set_aio_context(s->conf->conf.blk, s->ctx, &local_err);
     aio_context_release(old_context);
     if (r < 0) {
         error_report_err(local_err);
         goto fail_aio_context;
     }
 
     /* Process queued requests before the ones in vring */
     virtio_blk_process_queued_requests(vblk, false);
 
     /* Kick right away to begin processing requests already in vring */
     for (i = 0; i < nvqs; i++) {
         VirtQueue *vq = virtio_get_queue(s->vdev, i);
 
         event_notifier_set(virtio_queue_get_host_notifier(vq));
     }
 
     /* Get this show started by hooking up our callbacks */
     aio_context_acquire(s->ctx);
     for (i = 0; i < nvqs; i++) {
         VirtQueue *vq = virtio_get_queue(s->vdev, i);
 
         virtio_queue_aio_attach_host_notifier(vq, s->ctx);
     }
     aio_context_release(s->ctx);
     return 0;
 
   fail_aio_context:
     memory_region_transaction_begin();
 
     for (i = 0; i < nvqs; i++) {
         virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
     }
 
     memory_region_transaction_commit();
 
     for (i = 0; i < nvqs; i++) {
         virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
     }
   fail_host_notifiers:
     k->set_guest_notifiers(qbus->parent, nvqs, false);
   fail_guest_notifiers:
     /*
      * If we failed to set up the guest notifiers queued requests will be
      * processed on the main context.
      */
     virtio_blk_process_queued_requests(vblk, false);
     vblk->dataplane_disabled = true;
     s->starting = false;
     vblk->dataplane_started = true;
     return -ENOSYS;
 }
 
 /* Stop notifications for new requests from guest.
  *
  * Context: BH in IOThread
  */
 static void virtio_blk_data_plane_stop_bh(void *opaque)
 {
     VirtIOBlockDataPlane *s = opaque;
     unsigned i;
 
     for (i = 0; i < s->conf->num_queues; i++) {
         VirtQueue *vq = virtio_get_queue(s->vdev, i);
 
         virtio_queue_aio_detach_host_notifier(vq, s->ctx);
     }
 }
 
 /* Context: QEMU global mutex held */
 void virtio_blk_data_plane_stop(VirtIODevice *vdev)
 {
     VirtIOBlock *vblk = VIRTIO_BLK(vdev);
     VirtIOBlockDataPlane *s = vblk->dataplane;
     BusState *qbus = qdev_get_parent_bus(DEVICE(vblk));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
     unsigned i;
     unsigned nvqs = s->conf->num_queues;
 
     if (!vblk->dataplane_started || s->stopping) {
         return;
     }
 
     /* Better luck next time. */
     if (vblk->dataplane_disabled) {
         vblk->dataplane_disabled = false;
         vblk->dataplane_started = false;
         return;
     }
     s->stopping = true;
     trace_virtio_blk_data_plane_stop(s);
 
     aio_context_acquire(s->ctx);
     aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
 
     /* Drain and try to switch bs back to the QEMU main loop. If other users
      * keep the BlockBackend in the iothread, that's ok */
     blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context(), NULL);
 
     aio_context_release(s->ctx);
 
     /*
      * Batch all the host notifiers in a single transaction to avoid
      * quadratic time complexity in address_space_update_ioeventfds().
      */
     memory_region_transaction_begin();
 
     for (i = 0; i < nvqs; i++) {
         virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
     }
 
     /*
      * The transaction expects the ioeventfds to be open when it
      * commits. Do it now, before the cleanup loop.
      */
     memory_region_transaction_commit();
 
     for (i = 0; i < nvqs; i++) {
         virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
     }
 
     qemu_bh_cancel(s->bh);
     notify_guest_bh(s); /* final chance to notify guest */
 
     /* Clean up guest notifier (irq) */
     k->set_guest_notifiers(qbus->parent, nvqs, false);
 
     vblk->dataplane_started = false;
     s->stopping = false;
 }