virtio-scsi-dataplane: Code to run virtio-scsi on iothread

This implements the core part of dataplane feature of virtio-scsi.

A few fields are added in VirtIOSCSICommon to maintain the dataplane
status. These fields are managed by a new source file:
virtio-scsi-dataplane.c.

Most code in this file will run on an iothread, unless otherwise
commented as in a global mutex context, such as those functions to
start, stop and setting the iothread property.

Upon start, we set up guest/host event notifiers, in a same way as
virtio-blk does. The handlers then pop request from vring and call into
virtio-scsi.c functions to process it. So we need to make sure make all
those called functions work with iothread, too.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/Makefile.objs

@@ -8,6 +8,6 @@ common-obj-$(CONFIG_ESP_PCI) += esp-pci.o
 obj-$(CONFIG_PSERIES) += spapr_vscsi.o
 
 ifeq ($(CONFIG_VIRTIO),y)
-obj-y += virtio-scsi.o
+obj-y += virtio-scsi.o virtio-scsi-dataplane.o
 obj-$(CONFIG_VHOST_SCSI) += vhost-scsi.o
 endif

hw/scsi/virtio-scsi-dataplane.c

@@ -0,0 +1,222 @@
+/*
+ * Virtio SCSI dataplane
+ *
+ * Copyright Red Hat, Inc. 2014
+ *
+ * Authors:
+ *   Fam Zheng <famz@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 "hw/virtio/virtio-scsi.h"
+#include "qemu/error-report.h"
+#include <hw/scsi/scsi.h>
+#include <block/scsi.h>
+#include <hw/virtio/virtio-bus.h>
+#include "hw/virtio/virtio-access.h"
+#include "stdio.h"
+
+/* Context: QEMU global mutex held */
+void virtio_scsi_set_iothread(VirtIOSCSI *s, IOThread *iothread)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
+
+    assert(!s->ctx);
+    s->ctx = iothread_get_aio_context(vs->conf.iothread);
+
+    /* Don't try if transport does not support notifiers. */
+    if (!k->set_guest_notifiers || !k->set_host_notifier) {
+        fprintf(stderr, "virtio-scsi: Failed to set iothread "
+                   "(transport does not support notifiers)");
+        exit(1);
+    }
+}
+
+static VirtIOSCSIVring *virtio_scsi_vring_init(VirtIOSCSI *s,
+                                               VirtQueue *vq,
+                                               EventNotifierHandler *handler,
+                                               int n)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    VirtIOSCSIVring *r = g_slice_new(VirtIOSCSIVring);
+
+    /* Set up virtqueue notify */
+    if (k->set_host_notifier(qbus->parent, n, true) != 0) {
+        fprintf(stderr, "virtio-scsi: Failed to set host notifier\n");
+        exit(1);
+    }
+    r->host_notifier = *virtio_queue_get_host_notifier(vq);
+    r->guest_notifier = *virtio_queue_get_guest_notifier(vq);
+    aio_set_event_notifier(s->ctx, &r->host_notifier, handler);
+
+    r->parent = s;
+
+    if (!vring_setup(&r->vring, VIRTIO_DEVICE(s), n)) {
+        fprintf(stderr, "virtio-scsi: VRing setup failed\n");
+        exit(1);
+    }
+    return r;
+}
+
+VirtIOSCSIReq *virtio_scsi_pop_req_vring(VirtIOSCSI *s,
+                                         VirtIOSCSIVring *vring)
+{
+    VirtIOSCSIReq *req = virtio_scsi_init_req(s, NULL);
+    int r;
+
+    req->vring = vring;
+    r = vring_pop((VirtIODevice *)s, &vring->vring, &req->elem);
+    if (r < 0) {
+        virtio_scsi_free_req(req);
+        req = NULL;
+    }
+    return req;
+}
+
+void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req)
+{
+    vring_push(&req->vring->vring, &req->elem,
+               req->qsgl.size + req->resp_iov.size);
+    event_notifier_set(&req->vring->guest_notifier);
+}
+
+static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
+{
+    VirtIOSCSIVring *vring = container_of(notifier,
+                                          VirtIOSCSIVring, host_notifier);
+    VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
+    VirtIOSCSIReq *req;
+
+    event_notifier_test_and_clear(notifier);
+    while ((req = virtio_scsi_pop_req_vring(s, vring))) {
+        virtio_scsi_handle_ctrl_req(s, req);
+    }
+}
+
+static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
+{
+    VirtIOSCSIVring *vring = container_of(notifier,
+                                          VirtIOSCSIVring, host_notifier);
+    VirtIOSCSI *s = vring->parent;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    event_notifier_test_and_clear(notifier);
+
+    if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
+        return;
+    }
+
+    if (s->events_dropped) {
+        virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
+    }
+}
+
+static void virtio_scsi_iothread_handle_cmd(EventNotifier *notifier)
+{
+    VirtIOSCSIVring *vring = container_of(notifier,
+                                          VirtIOSCSIVring, host_notifier);
+    VirtIOSCSI *s = (VirtIOSCSI *)vring->parent;
+    VirtIOSCSIReq *req;
+
+    event_notifier_test_and_clear(notifier);
+    while ((req = virtio_scsi_pop_req_vring(s, vring))) {
+        virtio_scsi_handle_cmd_req(s, req);
+    }
+}
+
+/* Context: QEMU global mutex held */
+void virtio_scsi_dataplane_start(VirtIOSCSI *s)
+{
+    int i;
+    int rc;
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
+
+    if (s->dataplane_started ||
+        s->dataplane_starting ||
+        s->ctx != iothread_get_aio_context(vs->conf.iothread)) {
+        return;
+    }
+
+    s->dataplane_starting = true;
+
+    /* Set up guest notifier (irq) */
+    rc = k->set_guest_notifiers(qbus->parent, vs->conf.num_queues + 2, true);
+    if (rc != 0) {
+        fprintf(stderr, "virtio-scsi: Failed to set guest notifiers, "
+                "ensure -enable-kvm is set\n");
+        exit(1);
+    }
+
+    aio_context_acquire(s->ctx);
+    s->ctrl_vring = virtio_scsi_vring_init(s, vs->ctrl_vq,
+                                           virtio_scsi_iothread_handle_ctrl,
+                                           0);
+    s->event_vring = virtio_scsi_vring_init(s, vs->event_vq,
+                                            virtio_scsi_iothread_handle_event,
+                                            1);
+    s->cmd_vrings = g_malloc0(sizeof(VirtIOSCSIVring) * vs->conf.num_queues);
+    for (i = 0; i < vs->conf.num_queues; i++) {
+        s->cmd_vrings[i] =
+            virtio_scsi_vring_init(s, vs->cmd_vqs[i],
+                                   virtio_scsi_iothread_handle_cmd,
+                                   i + 2);
+    }
+
+    aio_context_release(s->ctx);
+    s->dataplane_starting = false;
+    s->dataplane_started = true;
+}
+
+/* Context: QEMU global mutex held */
+void virtio_scsi_dataplane_stop(VirtIOSCSI *s)
+{
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+    VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
+    int i;
+
+    if (!s->dataplane_started || s->dataplane_stopping) {
+        return;
+    }
+    s->dataplane_stopping = true;
+    assert(s->ctx == iothread_get_aio_context(vs->conf.iothread));
+
+    aio_context_acquire(s->ctx);
+
+    aio_set_event_notifier(s->ctx, &s->ctrl_vring->host_notifier, NULL);
+    aio_set_event_notifier(s->ctx, &s->event_vring->host_notifier, NULL);
+    for (i = 0; i < vs->conf.num_queues; i++) {
+        aio_set_event_notifier(s->ctx, &s->cmd_vrings[i]->host_notifier, NULL);
+    }
+
+    bdrv_drain_all(); /* ensure there are no in-flight requests */
+
+    aio_context_release(s->ctx);
+
+    /* Sync vring state back to virtqueue so that non-dataplane request
+     * processing can continue when we disable the host notifier below.
+     */
+    vring_teardown(&s->ctrl_vring->vring, vdev, 0);
+    vring_teardown(&s->event_vring->vring, vdev, 1);
+    for (i = 0; i < vs->conf.num_queues; i++) {
+        vring_teardown(&s->cmd_vrings[i]->vring, vdev, 2 + i);
+    }
+
+    for (i = 0; i < vs->conf.num_queues + 2; i++) {
+        k->set_host_notifier(qbus->parent, i, false);
+    }
+
+    /* Clean up guest notifier (irq) */
+    k->set_guest_notifiers(qbus->parent, vs->conf.num_queues + 2, false);
+    s->dataplane_stopping = false;
+    s->dataplane_started = false;
+}

include/hw/virtio/virtio-scsi.h

@@ -182,6 +182,18 @@ typedef struct VirtIOSCSI {
     SCSIBus bus;
     int resetting;
     bool events_dropped;
+
+    /* Fields for dataplane below */
+    AioContext *ctx; /* one iothread per virtio-scsi-pci for now */
+
+    /* Vring is used instead of vq in dataplane code, because of the underlying
+     * memory layer thread safety */
+    VirtIOSCSIVring *ctrl_vring;
+    VirtIOSCSIVring *event_vring;
+    VirtIOSCSIVring **cmd_vrings;
+    bool dataplane_started;
+    bool dataplane_starting;
+    bool dataplane_stopping;
 } VirtIOSCSI;
 
 typedef struct VirtIOSCSIReq {
@@ -248,4 +260,11 @@ void virtio_scsi_free_req(VirtIOSCSIReq *req);
 void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice *dev,
                             uint32_t event, uint32_t reason);
 
+void virtio_scsi_set_iothread(VirtIOSCSI *s, IOThread *iothread);
+void virtio_scsi_dataplane_start(VirtIOSCSI *s);
+void virtio_scsi_dataplane_stop(VirtIOSCSI *s);
+void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req);
+VirtIOSCSIReq *virtio_scsi_pop_req_vring(VirtIOSCSI *s,
+                                         VirtIOSCSIVring *vring);
+
 #endif /* _QEMU_VIRTIO_SCSI_H */