hw/block/dataplane/virtio-blk.c

   1 /*
   2  * Dedicated thread for virtio-blk I/O processing
   3  *
   4  * Copyright 2012 IBM, Corp.
   5  * Copyright 2012 Red Hat, Inc. and/or its affiliates
   6  *
   7  * Authors:
   8  *   Stefan Hajnoczi <stefanha@redhat.com>
   9  *
  10  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  11  * See the COPYING file in the top-level directory.
  12  *
  13  */
  14
  15 #include "trace.h"
  16 #include "qemu/iov.h"
  17 #include "qemu/thread.h"
  18 #include "qemu/error-report.h"
  19 #include "hw/virtio/virtio-access.h"
  20 #include "hw/virtio/dataplane/vring.h"
  21 #include "hw/virtio/dataplane/vring-accessors.h"
  22 #include "sysemu/block-backend.h"
  23 #include "hw/virtio/virtio-blk.h"
  24 #include "virtio-blk.h"
  25 #include "block/aio.h"
  26 #include "hw/virtio/virtio-bus.h"
  27 #include "qom/object_interfaces.h"
  28
  29 struct VirtIOBlockDataPlane {
  30     bool started;
  31     bool starting;
  32     bool stopping;
  33     bool disabled;
  34
  35     VirtIOBlkConf *conf;
  36
  37     VirtIODevice *vdev;
  38     Vring vring;                    /* virtqueue vring */
  39     EventNotifier *guest_notifier;  /* irq */
  40     QEMUBH *bh;                     /* bh for guest notification */
  41
  42     /* Note that these EventNotifiers are assigned by value.  This is
  43      * fine as long as you do not call event_notifier_cleanup on them
  44      * (because you don't own the file descriptor or handle; you just
  45      * use it).
  46      */
  47     IOThread *iothread;
  48     IOThread internal_iothread_obj;
  49     AioContext *ctx;
  50     EventNotifier host_notifier;    /* doorbell */
  51
  52     /* Operation blocker on BDS */
  53     Error *blocker;
  54     void (*saved_complete_request)(struct VirtIOBlockReq *req,
  55                                    unsigned char status);
  56 };
  57
  58 /* Raise an interrupt to signal guest, if necessary */
  59 static void notify_guest(VirtIOBlockDataPlane *s)
  60 {
  61     if (!vring_should_notify(s->vdev, &s->vring)) {
  62         return;
  63     }
  64
  65     event_notifier_set(s->guest_notifier);
  66 }
  67
  68 static void notify_guest_bh(void *opaque)
  69 {
  70     VirtIOBlockDataPlane *s = opaque;
  71
  72     notify_guest(s);
  73 }
  74
  75 static void complete_request_vring(VirtIOBlockReq *req, unsigned char status)
  76 {
  77     VirtIOBlockDataPlane *s = req->dev->dataplane;
  78     stb_p(&req->in->status, status);
  79
  80     vring_push(s->vdev, &req->dev->dataplane->vring, &req->elem, req->in_len);
  81
  82     /* Suppress notification to guest by BH and its scheduled
  83      * flag because requests are completed as a batch after io
  84      * plug & unplug is introduced, and the BH can still be
  85      * executed in dataplane aio context even after it is
  86      * stopped, so needn't worry about notification loss with BH.
  87      */
  88     qemu_bh_schedule(s->bh);
  89 }
  90
  91 static void handle_notify(EventNotifier *e)
  92 {
  93     VirtIOBlockDataPlane *s = container_of(e, VirtIOBlockDataPlane,
  94                                            host_notifier);
  95     VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
  96
  97     event_notifier_test_and_clear(&s->host_notifier);
  98     blk_io_plug(s->conf->conf.blk);
  99     for (;;) {
 100         MultiReqBuffer mrb = {};
 101         int ret;
 102
 103         /* Disable guest->host notifies to avoid unnecessary vmexits */
 104         vring_disable_notification(s->vdev, &s->vring);
 105
 106         for (;;) {
 107             VirtIOBlockReq *req = virtio_blk_alloc_request(vblk);
 108
 109             ret = vring_pop(s->vdev, &s->vring, &req->elem);
 110             if (ret < 0) {
 111                 virtio_blk_free_request(req);
 112                 break; /* no more requests */
 113             }
 114
 115             trace_virtio_blk_data_plane_process_request(s, req->elem.out_num,
 116                                                         req->elem.in_num,
 117                                                         req->elem.index);
 118
 119             virtio_blk_handle_request(req, &mrb);
 120         }
 121
 122         if (mrb.num_reqs) {
 123             virtio_blk_submit_multireq(s->conf->conf.blk, &mrb);
 124         }
 125
 126         if (likely(ret == -EAGAIN)) { /* vring emptied */
 127             /* Re-enable guest->host notifies and stop processing the vring.
 128              * But if the guest has snuck in more descriptors, keep processing.
 129              */
 130             if (vring_enable_notification(s->vdev, &s->vring)) {
 131                 break;
 132             }
 133         } else { /* fatal error */
 134             break;
 135         }
 136     }
 137     blk_io_unplug(s->conf->conf.blk);
 138 }
 139
 140 /* Context: QEMU global mutex held */
 141 void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
 142                                   VirtIOBlockDataPlane **dataplane,
 143                                   Error **errp)
 144 {
 145     VirtIOBlockDataPlane *s;
 146     Error *local_err = NULL;
 147     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
 148     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 149
 150     *dataplane = NULL;
 151
 152     if (!conf->data_plane && !conf->iothread) {
 153         return;
 154     }
 155
 156     /* Don't try if transport does not support notifiers. */
 157     if (!k->set_guest_notifiers || !k->set_host_notifier) {
 158         error_setg(errp,
 159                    "device is incompatible with x-data-plane "
 160                    "(transport does not support notifiers)");
 161         return;
 162     }
 163
 164     /* If dataplane is (re-)enabled while the guest is running there could be
 165      * block jobs that can conflict.
 166      */
 167     if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE,
 168                           &local_err)) {
 169         error_setg(errp, "cannot start dataplane thread: %s",
 170                    error_get_pretty(local_err));
 171         error_free(local_err);
 172         return;
 173     }
 174
 175     s = g_new0(VirtIOBlockDataPlane, 1);
 176     s->vdev = vdev;
 177     s->conf = conf;
 178
 179     if (conf->iothread) {
 180         s->iothread = conf->iothread;
 181         object_ref(OBJECT(s->iothread));
 182     } else {
 183         /* Create per-device IOThread if none specified.  This is for
 184          * x-data-plane option compatibility.  If x-data-plane is removed we
 185          * can drop this.
 186          */
 187         object_initialize(&s->internal_iothread_obj,
 188                           sizeof(s->internal_iothread_obj),
 189                           TYPE_IOTHREAD);
 190         user_creatable_complete(OBJECT(&s->internal_iothread_obj), &error_abort);
 191         s->iothread = &s->internal_iothread_obj;
 192     }
 193     s->ctx = iothread_get_aio_context(s->iothread);
 194     s->bh = aio_bh_new(s->ctx, notify_guest_bh, s);
 195
 196     error_setg(&s->blocker, "block device is in use by data plane");
 197     blk_op_block_all(conf->conf.blk, s->blocker);
 198     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_RESIZE, s->blocker);
 199     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_DRIVE_DEL, s->blocker);
 200     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_BACKUP_SOURCE, s->blocker);
 201     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_CHANGE, s->blocker);
 202     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_COMMIT_SOURCE, s->blocker);
 203     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_COMMIT_TARGET, s->blocker);
 204     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_EJECT, s->blocker);
 205     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_EXTERNAL_SNAPSHOT, s->blocker);
 206     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_INTERNAL_SNAPSHOT, s->blocker);
 207     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_INTERNAL_SNAPSHOT_DELETE,
 208                    s->blocker);
 209     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_MIRROR, s->blocker);
 210     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_STREAM, s->blocker);
 211     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_REPLACE, s->blocker);
 212
 213     *dataplane = s;
 214 }
 215
 216 /* Context: QEMU global mutex held */
 217 void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
 218 {
 219     if (!s) {
 220         return;
 221     }
 222
 223     virtio_blk_data_plane_stop(s);
 224     blk_op_unblock_all(s->conf->conf.blk, s->blocker);
 225     error_free(s->blocker);
 226     qemu_bh_delete(s->bh);
 227     object_unref(OBJECT(s->iothread));
 228     g_free(s);
 229 }
 230
 231 /* Context: QEMU global mutex held */
 232 void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
 233 {
 234     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
 235     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 236     VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
 237     VirtQueue *vq;
 238     int r;
 239
 240     if (s->started || s->disabled) {
 241         return;
 242     }
 243
 244     if (s->starting) {
 245         return;
 246     }
 247
 248     s->starting = true;
 249
 250     vq = virtio_get_queue(s->vdev, 0);
 251     if (!vring_setup(&s->vring, s->vdev, 0)) {
 252         goto fail_vring;
 253     }
 254
 255     /* Set up guest notifier (irq) */
 256     r = k->set_guest_notifiers(qbus->parent, 1, true);
 257     if (r != 0) {
 258         fprintf(stderr, "virtio-blk failed to set guest notifier (%d), "
 259                 "ensure -enable-kvm is set\n", r);
 260         goto fail_guest_notifiers;
 261     }
 262     s->guest_notifier = virtio_queue_get_guest_notifier(vq);
 263
 264     /* Set up virtqueue notify */
 265     r = k->set_host_notifier(qbus->parent, 0, true);
 266     if (r != 0) {
 267         fprintf(stderr, "virtio-blk failed to set host notifier (%d)\n", r);
 268         goto fail_host_notifier;
 269     }
 270     s->host_notifier = *virtio_queue_get_host_notifier(vq);
 271
 272     s->saved_complete_request = vblk->complete_request;
 273     vblk->complete_request = complete_request_vring;
 274
 275     s->starting = false;
 276     s->started = true;
 277     trace_virtio_blk_data_plane_start(s);
 278
 279     blk_set_aio_context(s->conf->conf.blk, s->ctx);
 280
 281     /* Kick right away to begin processing requests already in vring */
 282     event_notifier_set(virtio_queue_get_host_notifier(vq));
 283
 284     /* Get this show started by hooking up our callbacks */
 285     aio_context_acquire(s->ctx);
 286     aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
 287     aio_context_release(s->ctx);
 288     return;
 289
 290   fail_host_notifier:
 291     k->set_guest_notifiers(qbus->parent, 1, false);
 292   fail_guest_notifiers:
 293     vring_teardown(&s->vring, s->vdev, 0);
 294     s->disabled = true;
 295   fail_vring:
 296     s->starting = false;
 297 }
 298
 299 /* Context: QEMU global mutex held */
 300 void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
 301 {
 302     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
 303     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 304     VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
 305
 306
 307     /* Better luck next time. */
 308     if (s->disabled) {
 309         s->disabled = false;
 310         return;
 311     }
 312     if (!s->started || s->stopping) {
 313         return;
 314     }
 315     s->stopping = true;
 316     vblk->complete_request = s->saved_complete_request;
 317     trace_virtio_blk_data_plane_stop(s);
 318
 319     aio_context_acquire(s->ctx);
 320
 321     /* Stop notifications for new requests from guest */
 322     aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
 323
 324     /* Drain and switch bs back to the QEMU main loop */
 325     blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
 326
 327     aio_context_release(s->ctx);
 328
 329     /* Sync vring state back to virtqueue so that non-dataplane request
 330      * processing can continue when we disable the host notifier below.
 331      */
 332     vring_teardown(&s->vring, s->vdev, 0);
 333
 334     k->set_host_notifier(qbus->parent, 0, false);
 335
 336     /* Clean up guest notifier (irq) */
 337     k->set_guest_notifiers(qbus->parent, 1, false);
 338
 339     s->started = false;
 340     s->stopping = false;
 341 }