[Qemu-devel] [PATCH v3 00/12] Fix transactional snapshot with dataplane and NBD export

[Qemu-devel] [PATCH v3 00/12] Fix transactional snapshot with dataplane and NBD export

[Fam Zheng]

Changes from v2, which covers virtio-scsi as well:

  - Patch 1: Review all bdrv_op_block_all callers.
             Document bdrv_op_blocker_add_notifier.
             Fix blocking in bdrv_op_blocker_notify.
  - Patch 11: Commit message and function comment update.
  - Patch 12: New.

Reported by Paolo.

Unlike the iohandler in main loop, iothreads currently process the event
notifier used by virtio-blk ioeventfd in nested aio_poll. This is dangerous
without proper protection, because guest requests could sneak to block layer
where they mustn't.

For example, a QMP transaction may involve multiple bdrv_drain_all() in
handling the list of AioContext it works on. If an aio_poll in one of the
bdrv_drain_all() happens to process a guest VQ kick, and dispatches the
ioeventfd event to virtio-blk, a new guest write is then submitted, and voila,
the transaction semantics is violated.

This series avoids this problem by disabling virtio-blk handlers during
bdrv_drain_all() and transactions.

- Patches 1~3 add the block layer op blocker change notifier code.
- Patches 4,5 secure virtio-blk dataplane.
- Patch 6 secures nbd export.
- Patch 7~10 protect each transaction type from being voilated by new IO
  generated in nested aio_poll.
- Patch 11 protects bdrv_drain and bdrv_drain_all.
- Patch 12 does the same protection to virtio-scsi dataplane.


Fam Zheng (12):
  block: Add op blocker type "device IO"
  block: Add op blocker notifier list
  block-backend: Add blk_op_blocker_add_notifier
  virtio-blk: Move complete_request to 'ops' structure
  virtio-blk: Don't handle output when there is "device IO" op blocker
  nbd-server: Clear "can_read" when "device io" blocker is set
  blockdev: Block device IO during internal snapshot transaction
  blockdev: Block device IO during external snapshot transaction
  blockdev: Block device IO during drive-backup transaction
  blockdev: Block device IO during blockdev-backup transaction
  block: Block "device IO" during bdrv_drain and bdrv_drain_all
  virtio-scsi-dataplane: Add "device IO" op blocker listener

 block.c                         | 35 ++++++++++++++++
 block/block-backend.c           |  6 +++
 block/io.c                      | 22 +++++++++-
 blockdev.c                      | 49 ++++++++++++++++++----
 blockjob.c                      |  1 +
 hw/block/dataplane/virtio-blk.c | 37 ++++++++++++++---
 hw/block/virtio-blk.c           | 69 +++++++++++++++++++++++++++++--
 hw/scsi/virtio-scsi-dataplane.c | 91 ++++++++++++++++++++++++++++++++---------
 hw/scsi/virtio-scsi.c           |  4 ++
 include/block/block.h           |  9 ++++
 include/block/block_int.h       |  3 ++
 include/hw/virtio/virtio-blk.h  | 17 ++++++--
 include/hw/virtio/virtio-scsi.h |  3 ++
 include/sysemu/block-backend.h  |  2 +
 migration/block.c               |  1 +
 nbd.c                           | 18 ++++++++
 16 files changed, 327 insertions(+), 40 deletions(-)

-- 
2.4.0

[Qemu-devel] [PATCH v3 01/12] block: Add op blocker type "device IO"

[Fam Zheng]

It blocks device IO.

All bdrv_op_block_all/blk_op_block_all callers are taken care of:

- virtio_blk_data_plane_create
- virtio_scsi_hotplug

  Device creation, unblock it.

- bdrv_set_backing_hd

  Backing hd is not used by device, so blocking is OK.

- backup_start

  Blocking target when backup is running, unblock it.

- mirror_complete

  Blocking s->to_replace until mirror_exit, OK.

- block_job_complete

  The block job may be long running. Unblock it.

- init_blk_migration

  The block migration may be long running, Unblock it.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockjob.c                      | 1 +
 hw/block/dataplane/virtio-blk.c | 1 +
 hw/scsi/virtio-scsi.c           | 1 +
 include/block/block.h           | 1 +
 migration/block.c               | 1 +
 5 files changed, 5 insertions(+)

diff --git a/blockjob.c b/blockjob.c
index 2755465..e39bdde 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -51,6 +51,7 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
                BlockJobType_lookup[driver->job_type]);
     bdrv_op_block_all(bs, job->blocker);
     bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
+    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, job->blocker);
 
     job->driver        = driver;
     job->bs            = bs;
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 3db139b..3ecc8bd 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -209,6 +209,7 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_MIRROR, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_STREAM, s->blocker);
     blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_REPLACE, s->blocker);
+    blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
 
     *dataplane = s;
 }
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index e242fef..5e15fa6 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -772,6 +772,7 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
             return;
         }
         blk_op_block_all(sd->conf.blk, s->blocker);
+        blk_op_unblock(sd->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
         aio_context_acquire(s->ctx);
         blk_set_aio_context(sd->conf.blk, s->ctx);
         aio_context_release(s->ctx);
diff --git a/include/block/block.h b/include/block/block.h
index 7d1a717..906fb31 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -159,6 +159,7 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_RESIZE,
     BLOCK_OP_TYPE_STREAM,
     BLOCK_OP_TYPE_REPLACE,
+    BLOCK_OP_TYPE_DEVICE_IO,
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
diff --git a/migration/block.c b/migration/block.c
index ddb59cc..b833bac 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -379,6 +379,7 @@ static void init_blk_migration(QEMUFile *f)
         alloc_aio_bitmap(bmds);
         error_setg(&bmds->blocker, "block device is in use by migration");
         bdrv_op_block_all(bs, bmds->blocker);
+        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, bmds->blocker);
         bdrv_ref(bs);
 
         block_mig_state.total_sector_sum += sectors;
-- 
2.4.0

[Qemu-devel] [PATCH v3 02/12] block: Add op blocker notifier list

[Fam Zheng]

BDS users can register a notifier and get notified about op blocker
changes.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c                   | 35 +++++++++++++++++++++++++++++++++++
 include/block/block.h     |  8 ++++++++
 include/block/block_int.h |  3 +++
 3 files changed, 46 insertions(+)

diff --git a/block.c b/block.c
index 7904098..178e186 100644
--- a/block.c
+++ b/block.c
@@ -3375,6 +3375,19 @@ struct BdrvOpBlocker {
     QLIST_ENTRY(BdrvOpBlocker) list;
 };
 
+/* Add a notifier which will be notified when the first blocker of some type is
+ * added to bs, or when the last blocker is removed. The notifier handler
+ * should receive a BlockOpEvent data.
+ *
+ * Caller must hold bs->aio_context; the notifier handler is also called with
+ * it hold.
+ */
+void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
+                                  Notifier *notifier)
+{
+    notifier_list_add(&bs->op_blocker_notifiers, notifier);
+}
+
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
 {
     BdrvOpBlocker *blocker;
@@ -3391,26 +3404,48 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
     return false;
 }
 
+static void bdrv_op_blocker_notify(BlockDriverState *bs, BlockOpType op,
+                                   Error *reason, bool blocking)
+{
+    BlockOpEvent event = (BlockOpEvent) {
+        op = op,
+        reason = reason,
+        blocking = blocking,
+    };
+
+    notifier_list_notify(&bs->op_blocker_notifiers, &event);
+}
+
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
+    bool blocked;
     BdrvOpBlocker *blocker;
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
 
     blocker = g_new0(BdrvOpBlocker, 1);
     blocker->reason = reason;
+    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
     QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
+    if (!blocked) {
+        bdrv_op_blocker_notify(bs, op, reason, true);
+    }
 }
 
 void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
+    bool blocked;
     BdrvOpBlocker *blocker, *next;
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
+    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
     QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
         if (blocker->reason == reason) {
             QLIST_REMOVE(blocker, list);
             g_free(blocker);
         }
     }
+    if (blocked && QLIST_EMPTY(&bs->op_blockers[op])) {
+        bdrv_op_blocker_notify(bs, op, reason, false);
+    }
 }
 
 void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
diff --git a/include/block/block.h b/include/block/block.h
index 906fb31..3420b2c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -163,6 +163,12 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
+typedef struct {
+    BlockOpType type;
+    Error *reason;
+    bool blocking;
+} BlockOpEvent;
+
 void bdrv_iostatus_enable(BlockDriverState *bs);
 void bdrv_iostatus_reset(BlockDriverState *bs);
 void bdrv_iostatus_disable(BlockDriverState *bs);
@@ -491,6 +497,8 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
 void bdrv_ref(BlockDriverState *bs);
 void bdrv_unref(BlockDriverState *bs);
 
+void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
+                                  Notifier *notifier);
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);
 void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index db29b74..29d1c84 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -418,6 +418,9 @@ struct BlockDriverState {
     /* operation blockers */
     QLIST_HEAD(, BdrvOpBlocker) op_blockers[BLOCK_OP_TYPE_MAX];
 
+    /* Callback when one list in op_blockers has "empty" status change. */
+    NotifierList op_blocker_notifiers;
+
     /* long-running background operation */
     BlockJob *job;
 
-- 
2.4.0

[Qemu-devel] [PATCH v3 03/12] block-backend: Add blk_op_blocker_add_notifier

[Fam Zheng]

Forward the call to bdrv_op_blocker_add_notifier.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/block-backend.c          | 6 ++++++
 include/sysemu/block-backend.h | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/block/block-backend.c b/block/block-backend.c
index 93e46f3..16efe60 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -802,6 +802,12 @@ void blk_op_unblock_all(BlockBackend *blk, Error *reason)
     bdrv_op_unblock_all(blk->bs, reason);
 }
 
+void blk_op_blocker_add_notifier(BlockBackend *blk,
+                                 Notifier *notifier)
+{
+    bdrv_op_blocker_add_notifier(blk->bs, notifier);
+}
+
 AioContext *blk_get_aio_context(BlockBackend *blk)
 {
     return bdrv_get_aio_context(blk->bs);
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index b4a4d5e..cde9651 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -136,6 +136,8 @@ int blk_get_flags(BlockBackend *blk);
 int blk_get_max_transfer_length(BlockBackend *blk);
 void blk_set_guest_block_size(BlockBackend *blk, int align);
 void *blk_blockalign(BlockBackend *blk, size_t size);
+void blk_op_blocker_add_notifier(BlockBackend *blk,
+                                 Notifier *notifier);
 bool blk_op_is_blocked(BlockBackend *blk, BlockOpType op, Error **errp);
 void blk_op_unblock(BlockBackend *blk, BlockOpType op, Error *reason);
 void blk_op_block_all(BlockBackend *blk, Error *reason);
-- 
2.4.0

[Qemu-devel] [PATCH v3 04/12] virtio-blk: Move complete_request to 'ops' structure

[Fam Zheng]

Should more ops be added to differentiate code between dataplane and
non-dataplane, the new saved_ops approach will be cleaner than messing
with N pointers.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 13 ++++++++-----
 hw/block/virtio-blk.c           |  8 ++++++--
 include/hw/virtio/virtio-blk.h  |  9 +++++++--
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 3ecc8bd..e287e09 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -51,8 +51,7 @@ struct VirtIOBlockDataPlane {
 
     /* Operation blocker on BDS */
     Error *blocker;
-    void (*saved_complete_request)(struct VirtIOBlockReq *req,
-                                   unsigned char status);
+    const VirtIOBlockOps *saved_ops;
 };
 
 /* Raise an interrupt to signal guest, if necessary */
@@ -88,6 +87,10 @@ static void complete_request_vring(VirtIOBlockReq *req, unsigned char status)
     qemu_bh_schedule(s->bh);
 }
 
+static const VirtIOBlockOps virtio_blk_data_plane_ops = {
+    .complete_request = complete_request_vring,
+};
+
 static void handle_notify(EventNotifier *e)
 {
     VirtIOBlockDataPlane *s = container_of(e, VirtIOBlockDataPlane,
@@ -270,8 +273,8 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
     }
     s->host_notifier = *virtio_queue_get_host_notifier(vq);
 
-    s->saved_complete_request = vblk->complete_request;
-    vblk->complete_request = complete_request_vring;
+    s->saved_ops = vblk->ops;
+    vblk->ops = &virtio_blk_data_plane_ops;
 
     s->starting = false;
     s->started = true;
@@ -314,7 +317,7 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
         return;
     }
     s->stopping = true;
-    vblk->complete_request = s->saved_complete_request;
+    vblk->ops = s->saved_ops;
     trace_virtio_blk_data_plane_stop(s);
 
     aio_context_acquire(s->ctx);
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index e6afe97..f4a9d19 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -59,9 +59,13 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
     virtio_notify(vdev, s->vq);
 }
 
+static const VirtIOBlockOps virtio_blk_ops = (VirtIOBlockOps) {
+    .complete_request = virtio_blk_complete_request,
+};
+
 static void virtio_blk_req_complete(VirtIOBlockReq *req, unsigned char status)
 {
-    req->dev->complete_request(req, status);
+    req->dev->ops->complete_request(req, status);
 }
 
 static int virtio_blk_handle_rw_error(VirtIOBlockReq *req, int error,
@@ -905,7 +909,7 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     s->sector_mask = (s->conf.conf.logical_block_size / BDRV_SECTOR_SIZE) - 1;
 
     s->vq = virtio_add_queue(vdev, 128, virtio_blk_handle_output);
-    s->complete_request = virtio_blk_complete_request;
+    s->ops = &virtio_blk_ops;
     virtio_blk_data_plane_create(vdev, conf, &s->dataplane, &err);
     if (err != NULL) {
         error_propagate(errp, err);
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 6bf5905..28b3436 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -44,6 +44,12 @@ struct VirtIOBlkConf
 struct VirtIOBlockDataPlane;
 
 struct VirtIOBlockReq;
+
+typedef struct {
+    /* Function to push to vq and notify guest */
+    void (*complete_request)(struct VirtIOBlockReq *req, unsigned char status);
+} VirtIOBlockOps;
+
 typedef struct VirtIOBlock {
     VirtIODevice parent_obj;
     BlockBackend *blk;
@@ -54,8 +60,7 @@ typedef struct VirtIOBlock {
     unsigned short sector_mask;
     bool original_wce;
     VMChangeStateEntry *change;
-    /* Function to push to vq and notify guest */
-    void (*complete_request)(struct VirtIOBlockReq *req, unsigned char status);
+    const VirtIOBlockOps *ops;
     Notifier migration_state_notifier;
     struct VirtIOBlockDataPlane *dataplane;
 } VirtIOBlock;
-- 
2.4.0

[Qemu-devel] [PATCH v3 05/12] virtio-blk: Don't handle output when there is "device IO" op blocker

[Fam Zheng]

virtio-blk now listens to op blocker change of the associated block
backend.

Up on setting op blocker on BLOCK_OP_TYPE_DEVICE_IO:

  non-dataplane:
   1) Set VirtIOBlock.paused
   2) In virtio_blk_handle_output, do nothing if VirtIOBlock.paused

  dataplane:
   1) Clear the host event notifier
   2) In handle_notify, do nothing if VirtIOBlock.paused

Up on removing the op blocker:

  non-dataplane:
   1) Clear VirtIOBlock.paused
   2) Schedule a BH on the AioContext of the backend, which calls
   virtio_blk_handle_output, so that the previous unhandled kicks can
   make progress

  dataplane:
   1) Set the host event notifier
   2) Notify the host event notifier so that unhandled events are
   processed

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 25 +++++++++++++++-
 hw/block/virtio-blk.c           | 63 +++++++++++++++++++++++++++++++++++++++--
 include/hw/virtio/virtio-blk.h  |  8 +++++-
 3 files changed, 92 insertions(+), 4 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index e287e09..a5e8e35 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -87,8 +87,28 @@ static void complete_request_vring(VirtIOBlockReq *req, unsigned char status)
     qemu_bh_schedule(s->bh);
 }
 
+static void virtio_blk_data_plane_pause(VirtIOBlock *vblk)
+{
+    VirtIOBlockDataPlane *s = vblk->dataplane;
+
+    event_notifier_test_and_clear(&s->host_notifier);
+    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
+}
+
+static void handle_notify(EventNotifier *e);
+static void virtio_blk_data_plane_resume(VirtIOBlock *vblk)
+{
+    VirtIOBlockDataPlane *s = vblk->dataplane;
+
+    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
+
+    event_notifier_set(&s->host_notifier);
+}
+
 static const VirtIOBlockOps virtio_blk_data_plane_ops = {
-    .complete_request = complete_request_vring,
+    .complete_request           = complete_request_vring,
+    .pause                      = virtio_blk_data_plane_pause,
+    .resume                     = virtio_blk_data_plane_resume,
 };
 
 static void handle_notify(EventNotifier *e)
@@ -98,6 +118,9 @@ static void handle_notify(EventNotifier *e)
     VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
 
     event_notifier_test_and_clear(&s->host_notifier);
+    if (vblk->paused) {
+        return;
+    }
     blk_io_plug(s->conf->conf.blk);
     for (;;) {
         MultiReqBuffer mrb = {};
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index f4a9d19..4bc1b2a 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -59,8 +59,38 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
     virtio_notify(vdev, s->vq);
 }
 
+typedef struct {
+    QEMUBH *bh;
+    VirtIOBlock *s;
+} VirtIOBlockResumeData;
+
+static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq);
+static void virtio_blk_resume_bh_cb(void *opaque)
+{
+    VirtIOBlockResumeData *data = opaque;
+    qemu_bh_delete(data->bh);
+    virtio_blk_handle_output(VIRTIO_DEVICE(data->s), data->s->vq);
+}
+
+static void virtio_blk_pause(VirtIOBlock *vblk)
+{
+    /* TODO: stop ioeventfd */
+}
+
+static void virtio_blk_resume(VirtIOBlock *vblk)
+{
+    VirtIOBlockResumeData *data = g_new(VirtIOBlockResumeData, 1);
+    data->bh = aio_bh_new(blk_get_aio_context(vblk->blk),
+            virtio_blk_resume_bh_cb, data);
+    data->s = vblk;
+    data->s->paused = false;
+    qemu_bh_schedule(data->bh);
+}
+
 static const VirtIOBlockOps virtio_blk_ops = (VirtIOBlockOps) {
-    .complete_request = virtio_blk_complete_request,
+    .complete_request           = virtio_blk_complete_request,
+    .pause                      = virtio_blk_pause,
+    .resume                     = virtio_blk_resume,
 };
 
 static void virtio_blk_req_complete(VirtIOBlockReq *req, unsigned char status)
@@ -597,6 +627,9 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     VirtIOBlockReq *req;
     MultiReqBuffer mrb = {};
 
+    if (s->paused) {
+        return;
+    }
     /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
      * dataplane here instead of waiting for .set_status().
      */
@@ -787,7 +820,7 @@ static void virtio_blk_save(QEMUFile *f, void *opaque)
 
     virtio_save(vdev, f);
 }
-    
+
 static void virtio_blk_save_device(VirtIODevice *vdev, QEMUFile *f)
 {
     VirtIOBlock *s = VIRTIO_BLK(vdev);
@@ -875,6 +908,29 @@ static void virtio_blk_migration_state_changed(Notifier *notifier, void *data)
     }
 }
 
+static void virtio_blk_op_blocker_changed(Notifier *notifier, void *opaque)
+{
+    BlockOpEvent *event = opaque;
+    VirtIOBlock *s = container_of(notifier, VirtIOBlock,
+                                  op_blocker_notifier);
+    bool pause;
+
+    if (event->type != BLOCK_OP_TYPE_DEVICE_IO) {
+        return;
+    }
+    pause = event->blocking || blk_op_is_blocked(s->blk,
+                                                    BLOCK_OP_TYPE_DEVICE_IO,
+                                                    NULL);
+    if (pause == s->paused) {
+        return;
+    }
+    if (pause) {
+        s->ops->pause(s);
+    } else {
+        s->ops->resume(s);
+    }
+}
+
 static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -926,6 +982,9 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     blk_set_guest_block_size(s->blk, s->conf.conf.logical_block_size);
 
     blk_iostatus_enable(s->blk);
+
+    s->op_blocker_notifier.notify = virtio_blk_op_blocker_changed;
+    blk_op_blocker_add_notifier(s->blk, &s->op_blocker_notifier);
 }
 
 static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 28b3436..aa15fea 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -42,12 +42,16 @@ struct VirtIOBlkConf
 };
 
 struct VirtIOBlockDataPlane;
-
+struct VirtIOBlock;
 struct VirtIOBlockReq;
 
 typedef struct {
     /* Function to push to vq and notify guest */
     void (*complete_request)(struct VirtIOBlockReq *req, unsigned char status);
+
+    /* Functions to pause/resume request handling */
+    void (*pause)(struct VirtIOBlock *vblk);
+    void (*resume)(struct VirtIOBlock *vblk);
 } VirtIOBlockOps;
 
 typedef struct VirtIOBlock {
@@ -62,6 +66,8 @@ typedef struct VirtIOBlock {
     VMChangeStateEntry *change;
     const VirtIOBlockOps *ops;
     Notifier migration_state_notifier;
+    Notifier op_blocker_notifier;
+    bool paused;
     struct VirtIOBlockDataPlane *dataplane;
 } VirtIOBlock;
 
-- 
2.4.0

[Qemu-devel] [PATCH v3 06/12] nbd-server: Clear "can_read" when "device io" blocker is set

[Fam Zheng]

So that NBD export cannot submit IO during bdrv_drain_all().

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 nbd.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/nbd.c b/nbd.c
index 06b501b..7d9d3e4 100644
--- a/nbd.c
+++ b/nbd.c
@@ -160,6 +160,8 @@ struct NBDExport {
     uint32_t nbdflags;
     QTAILQ_HEAD(, NBDClient) clients;
     QTAILQ_ENTRY(NBDExport) next;
+    Notifier blocker_notifier;
+    bool io_blocked;
 
     AioContext *ctx;
 };
@@ -1053,6 +1055,16 @@ static void blk_aio_detach(void *opaque)
     exp->ctx = NULL;
 }
 
+static void nbd_op_blocker_changed(Notifier *notifier, void *data)
+{
+    BlockOpEvent *event = data;
+    NBDExport *exp = container_of(notifier, NBDExport, blocker_notifier);
+    if (event->type != BLOCK_OP_TYPE_DEVICE_IO) {
+        return;
+    }
+    exp->io_blocked = event->blocking;
+}
+
 NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
                           uint32_t nbdflags, void (*close)(NBDExport *),
                           Error **errp)
@@ -1081,6 +1093,8 @@ NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
      * access since the export could be available before migration handover.
      */
     blk_invalidate_cache(blk, NULL);
+    exp->blocker_notifier.notify = nbd_op_blocker_changed;
+    blk_op_blocker_add_notifier(blk, &exp->blocker_notifier);
     return exp;
 
 fail:
@@ -1132,6 +1146,7 @@ void nbd_export_close(NBDExport *exp)
     nbd_export_set_name(exp, NULL);
     nbd_export_put(exp);
     if (exp->blk) {
+        notifier_remove(&exp->blocker_notifier);
         blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
                                         blk_aio_detach, exp);
         blk_unref(exp->blk);
@@ -1455,6 +1470,9 @@ static void nbd_update_can_read(NBDClient *client)
     bool can_read = client->recv_coroutine ||
                     client->nb_requests < MAX_NBD_REQUESTS;
 
+    if (client->exp && client->exp->io_blocked) {
+        can_read = false;
+    }
     if (can_read != client->can_read) {
         client->can_read = can_read;
         nbd_set_handlers(client);
-- 
2.4.0

[Qemu-devel] [PATCH v3 07/12] blockdev: Block device IO during internal snapshot transaction

[Fam Zheng]

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 5eaf77e..7f763d9 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1262,6 +1262,7 @@ typedef struct InternalSnapshotState {
     BlockDriverState *bs;
     AioContext *aio_context;
     QEMUSnapshotInfo sn;
+    Error *blocker;
 } InternalSnapshotState;
 
 static void internal_snapshot_prepare(BlkTransactionState *common,
@@ -1300,6 +1301,10 @@ static void internal_snapshot_prepare(BlkTransactionState *common,
     state->aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(state->aio_context);
 
+    state->bs = bs;
+    error_setg(&state->blocker, "internal snapshot in progress");
+    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+
     if (!bdrv_is_inserted(bs)) {
         error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
         return;
@@ -1354,9 +1359,6 @@ static void internal_snapshot_prepare(BlkTransactionState *common,
                          name, device);
         return;
     }
-
-    /* 4. succeed, mark a snapshot is created */
-    state->bs = bs;
 }
 
 static void internal_snapshot_abort(BlkTransactionState *common)
@@ -1387,6 +1389,10 @@ static void internal_snapshot_clean(BlkTransactionState *common)
     InternalSnapshotState *state = DO_UPCAST(InternalSnapshotState,
                                              common, common);
 
+    if (state->bs) {
+        bdrv_op_unblock(state->bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+        error_free(state->blocker);
+    }
     if (state->aio_context) {
         aio_context_release(state->aio_context);
     }
-- 
2.4.0

[Qemu-devel] [PATCH v3 08/12] blockdev: Block device IO during external snapshot transaction

[Fam Zheng]

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 7f763d9..923fc90 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1404,6 +1404,7 @@ typedef struct ExternalSnapshotState {
     BlockDriverState *old_bs;
     BlockDriverState *new_bs;
     AioContext *aio_context;
+    Error *blocker;
 } ExternalSnapshotState;
 
 static void external_snapshot_prepare(BlkTransactionState *common,
@@ -1525,6 +1526,9 @@ static void external_snapshot_prepare(BlkTransactionState *common,
     if (ret != 0) {
         error_propagate(errp, local_err);
     }
+
+    error_setg(&state->blocker, "snapshot in progress");
+    bdrv_op_block(state->old_bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
 }
 
 static void external_snapshot_commit(BlkTransactionState *common)
@@ -1541,8 +1545,6 @@ static void external_snapshot_commit(BlkTransactionState *common)
      * don't want to abort all of them if one of them fails the reopen */
     bdrv_reopen(state->new_bs, state->new_bs->open_flags & ~BDRV_O_RDWR,
                 NULL);
-
-    aio_context_release(state->aio_context);
 }
 
 static void external_snapshot_abort(BlkTransactionState *common)
@@ -1552,6 +1554,17 @@ static void external_snapshot_abort(BlkTransactionState *common)
     if (state->new_bs) {
         bdrv_unref(state->new_bs);
     }
+}
+
+static void external_snapshot_clean(BlkTransactionState *common)
+{
+    ExternalSnapshotState *state =
+                             DO_UPCAST(ExternalSnapshotState, common, common);
+
+    if (state->old_bs) {
+        bdrv_op_unblock(state->old_bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+        error_free(state->blocker);
+    }
     if (state->aio_context) {
         aio_context_release(state->aio_context);
     }
@@ -1716,6 +1729,7 @@ static const BdrvActionOps actions[] = {
         .prepare  = external_snapshot_prepare,
         .commit   = external_snapshot_commit,
         .abort = external_snapshot_abort,
+        .clean = external_snapshot_clean,
     },
     [TRANSACTION_ACTION_KIND_DRIVE_BACKUP] = {
         .instance_size = sizeof(DriveBackupState),
-- 
2.4.0

[Qemu-devel] [PATCH v3 09/12] blockdev: Block device IO during drive-backup transaction

[Fam Zheng]

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 923fc90..ae52d27 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1575,6 +1575,7 @@ typedef struct DriveBackupState {
     BlockDriverState *bs;
     AioContext *aio_context;
     BlockJob *job;
+    Error *blocker;
 } DriveBackupState;
 
 static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
@@ -1599,6 +1600,9 @@ static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
     state->aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(state->aio_context);
 
+    state->bs = bs;
+    error_setg(&state->blocker, "drive-backup in progress");
+    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
     qmp_drive_backup(backup->device, backup->target,
                      backup->has_format, backup->format,
                      backup->sync,
@@ -1613,7 +1617,6 @@ static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
         return;
     }
 
-    state->bs = bs;
     state->job = state->bs->job;
 }
 
@@ -1632,6 +1635,10 @@ static void drive_backup_clean(BlkTransactionState *common)
 {
     DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
 
+    if (state->bs) {
+        bdrv_op_unblock(state->bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+        error_free(state->blocker);
+    }
     if (state->aio_context) {
         aio_context_release(state->aio_context);
     }
-- 
2.4.0

[Qemu-devel] [PATCH v3 10/12] blockdev: Block device IO during blockdev-backup transaction

[Fam Zheng]

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 blockdev.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index ae52d27..bd28183 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1649,6 +1649,7 @@ typedef struct BlockdevBackupState {
     BlockDriverState *bs;
     BlockJob *job;
     AioContext *aio_context;
+    Error *blocker;
 } BlockdevBackupState;
 
 static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
@@ -1685,6 +1686,10 @@ static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
     }
     aio_context_acquire(state->aio_context);
 
+    state->bs = bs;
+    error_setg(&state->blocker, "blockdev-backup in progress");
+    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+
     qmp_blockdev_backup(backup->device, backup->target,
                         backup->sync,
                         backup->has_speed, backup->speed,
@@ -1696,7 +1701,6 @@ static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
         return;
     }
 
-    state->bs = bs;
     state->job = state->bs->job;
 }
 
@@ -1715,6 +1719,10 @@ static void blockdev_backup_clean(BlkTransactionState *common)
 {
     BlockdevBackupState *state = DO_UPCAST(BlockdevBackupState, common, common);
 
+    if (state->bs) {
+        bdrv_op_unblock(state->bs, BLOCK_OP_TYPE_DEVICE_IO, state->blocker);
+        error_free(state->blocker);
+    }
     if (state->aio_context) {
         aio_context_release(state->aio_context);
     }
-- 
2.4.0

[Qemu-devel] [PATCH v3 11/12] block: Block "device IO" during bdrv_drain and bdrv_drain_all

[Fam Zheng]

We don't want new requests from guest, so block the operation around the
nested poll.

It also avoids looping forever when iothread is submitting a lot of requests.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/io.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/block/io.c b/block/io.c
index 1ce62c4..b23a83f 100644
--- a/block/io.c
+++ b/block/io.c
@@ -286,12 +286,21 @@ static bool bdrv_drain_one(BlockDriverState *bs)
  *
  * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
  * AioContext.
+ *
+ * Devices are paused to avoid looping forever because otherwise they could
+ * keep submitting more requests.
  */
 void bdrv_drain(BlockDriverState *bs)
 {
+    Error *blocker = NULL;
+
+    error_setg(&blocker, "bdrv_drain in progress");
+    bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
     while (bdrv_drain_one(bs)) {
         /* Keep iterating */
     }
+    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
+    error_free(blocker);
 }
 
 /*
@@ -303,14 +312,20 @@ void bdrv_drain(BlockDriverState *bs)
  * Note that completion of an asynchronous I/O operation can trigger any
  * number of other I/O operations on other devices---for example a coroutine
  * can be arbitrarily complex and a constant flow of I/O can come until the
- * coroutine is complete.  Because of this, it is not possible to have a
- * function to drain a single device's I/O queue.
+ * coroutine is complete.  Because of this, we must call bdrv_drain_one in a
+ * loop.
+ *
+ * We explicitly pause block jobs and devices to prevent them from submitting
+ * more requests.
  */
 void bdrv_drain_all(void)
 {
     /* Always run first iteration so any pending completion BHs run */
     bool busy = true;
     BlockDriverState *bs = NULL;
+    Error *blocker = NULL;
+
+    error_setg(&blocker, "bdrv_drain_all in progress");
 
     while ((bs = bdrv_next(bs))) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
@@ -319,6 +334,7 @@ void bdrv_drain_all(void)
         if (bs->job) {
             block_job_pause(bs->job);
         }
+        bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
         aio_context_release(aio_context);
     }
 
@@ -343,8 +359,10 @@ void bdrv_drain_all(void)
         if (bs->job) {
             block_job_resume(bs->job);
         }
+        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
         aio_context_release(aio_context);
     }
+    error_free(blocker);
 }
 
 /**
-- 
2.4.0

[Qemu-devel] [PATCH v3 12/12] virtio-scsi-dataplane: Add "device IO" op blocker listener

[Fam Zheng]

When a disk is attached to scsi-bus, virtio_scsi_hotplug will take care
of protecting the block device with op blockers. Currently we haven't
enabled block jobs (like what's done in virtio_blk_data_plane_create),
but it is necessary to honor "device IO" op blocker first before we do.
This is useful to make sure that guest IO requests are paused during qmp
transactions (such as multi-disk snapshot or backup).

A counter is added to the virtio-scsi device, which keeps track of
currently blocked disks. If it goes from 0 to 1, the ioeventfds are
disabled; when it goes back to 0, they are re-enabled.

Also in device initialization, push the enabling of ioeventfds to before
return, so the virtio_scsi_clear_aio is not needed there. Rename it,
pair with an enabling variant, fix one coding style issue, then use it
in the device pause points.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/scsi/virtio-scsi-dataplane.c | 91 ++++++++++++++++++++++++++++++++---------
 hw/scsi/virtio-scsi.c           |  3 ++
 include/hw/virtio/virtio-scsi.h |  3 ++
 3 files changed, 77 insertions(+), 20 deletions(-)

diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index 5575648..18fdf69 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -40,7 +40,6 @@ void virtio_scsi_set_iothread(VirtIOSCSI *s, IOThread *iothread)
 
 static VirtIOSCSIVring *virtio_scsi_vring_init(VirtIOSCSI *s,
                                                VirtQueue *vq,
-                                               EventNotifierHandler *handler,
                                                int n)
 {
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
@@ -60,7 +59,6 @@ static VirtIOSCSIVring *virtio_scsi_vring_init(VirtIOSCSI *s,
     r = g_slice_new(VirtIOSCSIVring);
     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;
 
@@ -71,7 +69,6 @@ static VirtIOSCSIVring *virtio_scsi_vring_init(VirtIOSCSI *s,
     return r;
 
 fail_vring:
-    aio_set_event_notifier(s->ctx, &r->host_notifier, NULL);
     k->set_host_notifier(qbus->parent, n, false);
     g_slice_free(VirtIOSCSIVring, r);
     return NULL;
@@ -104,6 +101,9 @@ void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req)
     }
 }
 
+static void virtio_scsi_start_ioeventfd(VirtIOSCSI *s);
+static void virtio_scsi_stop_ioeventfd(VirtIOSCSI *s);
+
 static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
 {
     VirtIOSCSIVring *vring = container_of(notifier,
@@ -111,6 +111,10 @@ static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
     VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
     VirtIOSCSIReq *req;
 
+    if (s->pause_counter) {
+        virtio_scsi_stop_ioeventfd(s);
+        return;
+    }
     event_notifier_test_and_clear(notifier);
     while ((req = virtio_scsi_pop_req_vring(s, vring))) {
         virtio_scsi_handle_ctrl_req(s, req);
@@ -124,6 +128,10 @@ static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
     VirtIOSCSI *s = vring->parent;
     VirtIODevice *vdev = VIRTIO_DEVICE(s);
 
+    if (s->pause_counter) {
+        virtio_scsi_stop_ioeventfd(s);
+        return;
+    }
     event_notifier_test_and_clear(notifier);
 
     if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
@@ -143,6 +151,10 @@ static void virtio_scsi_iothread_handle_cmd(EventNotifier *notifier)
     VirtIOSCSIReq *req, *next;
     QTAILQ_HEAD(, VirtIOSCSIReq) reqs = QTAILQ_HEAD_INITIALIZER(reqs);
 
+    if (s->pause_counter) {
+        virtio_scsi_stop_ioeventfd(s);
+        return;
+    }
     event_notifier_test_and_clear(notifier);
     while ((req = virtio_scsi_pop_req_vring(s, vring))) {
         if (virtio_scsi_handle_cmd_req_prepare(s, req)) {
@@ -155,8 +167,56 @@ static void virtio_scsi_iothread_handle_cmd(EventNotifier *notifier)
     }
 }
 
+void virtio_scsi_dataplane_blocker_notify(Notifier *notifier,
+                                          void *data)
+{
+    VirtIOSCSI *s = container_of(notifier, VirtIOSCSI, blocker_notifier);
+    BlockOpEvent *event = data;
+
+    if (event->type != BLOCK_OP_TYPE_DEVICE_IO) {
+        return;
+    }
+    if (event->blocking) {
+        s->pause_counter++;
+        if (s->pause_counter == 1) {
+            virtio_scsi_stop_ioeventfd(s);
+        }
+    } else {
+        s->pause_counter--;
+        if (s->pause_counter == 0) {
+            virtio_scsi_start_ioeventfd(s);
+        }
+    }
+    assert(s->pause_counter >= 0);
+}
+
 /* assumes s->ctx held */
-static void virtio_scsi_clear_aio(VirtIOSCSI *s)
+static void virtio_scsi_start_ioeventfd(VirtIOSCSI *s)
+{
+    VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
+    int i;
+
+    if (!s->dataplane_started || s->dataplane_stopping) {
+        return;
+    }
+    if (s->ctrl_vring) {
+        aio_set_event_notifier(s->ctx, &s->ctrl_vring->host_notifier,
+                               virtio_scsi_iothread_handle_ctrl);
+    }
+    if (s->event_vring) {
+        aio_set_event_notifier(s->ctx, &s->event_vring->host_notifier,
+                               virtio_scsi_iothread_handle_event);
+    }
+    if (s->cmd_vrings) {
+        for (i = 0; i < vs->conf.num_queues && s->cmd_vrings[i]; i++) {
+            aio_set_event_notifier(s->ctx, &s->cmd_vrings[i]->host_notifier,
+                                   virtio_scsi_iothread_handle_cmd);
+        }
+    }
+}
+
+/* assumes s->ctx held */
+static void virtio_scsi_stop_ioeventfd(VirtIOSCSI *s)
 {
     VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
     int i;
@@ -169,7 +229,8 @@ static void virtio_scsi_clear_aio(VirtIOSCSI *s)
     }
     if (s->cmd_vrings) {
         for (i = 0; i < vs->conf.num_queues && s->cmd_vrings[i]; i++) {
-            aio_set_event_notifier(s->ctx, &s->cmd_vrings[i]->host_notifier, NULL);
+            aio_set_event_notifier(s->ctx, &s->cmd_vrings[i]->host_notifier,
+                                   NULL);
         }
     }
 }
@@ -229,24 +290,18 @@ void virtio_scsi_dataplane_start(VirtIOSCSI *s)
     }
 
     aio_context_acquire(s->ctx);
-    s->ctrl_vring = virtio_scsi_vring_init(s, vs->ctrl_vq,
-                                           virtio_scsi_iothread_handle_ctrl,
-                                           0);
+    s->ctrl_vring = virtio_scsi_vring_init(s, vs->ctrl_vq, 0);
     if (!s->ctrl_vring) {
         goto fail_vrings;
     }
-    s->event_vring = virtio_scsi_vring_init(s, vs->event_vq,
-                                            virtio_scsi_iothread_handle_event,
-                                            1);
+    s->event_vring = virtio_scsi_vring_init(s, vs->event_vq, 1);
     if (!s->event_vring) {
         goto fail_vrings;
     }
     s->cmd_vrings = g_new(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);
+            virtio_scsi_vring_init(s, vs->cmd_vqs[i], i + 2);
         if (!s->cmd_vrings[i]) {
             goto fail_vrings;
         }
@@ -254,11 +309,11 @@ void virtio_scsi_dataplane_start(VirtIOSCSI *s)
 
     s->dataplane_starting = false;
     s->dataplane_started = true;
+    virtio_scsi_start_ioeventfd(s);
     aio_context_release(s->ctx);
     return;
 
 fail_vrings:
-    virtio_scsi_clear_aio(s);
     aio_context_release(s->ctx);
     virtio_scsi_vring_teardown(s);
     for (i = 0; i < vs->conf.num_queues + 2; i++) {
@@ -290,11 +345,7 @@ void virtio_scsi_dataplane_stop(VirtIOSCSI *s)
 
     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);
-    }
+    virtio_scsi_stop_ioeventfd(s);
 
     blk_drain_all(); /* ensure there are no in-flight requests */
 
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 5e15fa6..16c253f 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -775,6 +775,8 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
         blk_op_unblock(sd->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
         aio_context_acquire(s->ctx);
         blk_set_aio_context(sd->conf.blk, s->ctx);
+        s->blocker_notifier.notify = virtio_scsi_dataplane_blocker_notify;
+        blk_op_blocker_add_notifier(sd->conf.blk, &s->blocker_notifier);
         aio_context_release(s->ctx);
     }
 
@@ -799,6 +801,7 @@ static void virtio_scsi_hotunplug(HotplugHandler *hotplug_dev, DeviceState *dev,
     }
 
     if (s->ctx) {
+        notifier_remove(&s->blocker_notifier);
         blk_op_unblock_all(sd->conf.blk, s->blocker);
     }
     qdev_simple_device_unplug_cb(hotplug_dev, dev, errp);
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index b42e7f1..f8591fd 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -97,6 +97,8 @@ typedef struct VirtIOSCSI {
     bool dataplane_disabled;
     bool dataplane_fenced;
     Error *blocker;
+    Notifier blocker_notifier;
+    int pause_counter;
     Notifier migration_state_notifier;
     uint32_t host_features;
 } VirtIOSCSI;
@@ -170,6 +172,7 @@ 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_blocker_notify(Notifier *notifier, void *data);
 void virtio_scsi_dataplane_start(VirtIOSCSI *s);
 void virtio_scsi_dataplane_stop(VirtIOSCSI *s);
 void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req);
-- 
2.4.0

Re: [Qemu-devel] [PATCH v3 01/12] block: Add op blocker type "device IO"

[Wen Congyang]

On 05/15/2015 02:04 PM, Fam Zheng wrote:
> It blocks device IO.

I am reading mirror codes recently, and have a question:
When block job mirror is finished, the source and target is synced. But we
call bdrv_swap() later(in bh context). Can the guest write something to
the source before the bh is scheduled? If the answer is yes, I think
we should use this to block the guest's disk I/O.

Thanks
Wen Congyang

> 
> All bdrv_op_block_all/blk_op_block_all callers are taken care of:
> 
> - virtio_blk_data_plane_create
> - virtio_scsi_hotplug
> 
>   Device creation, unblock it.
> 
> - bdrv_set_backing_hd
> 
>   Backing hd is not used by device, so blocking is OK.
> 
> - backup_start
> 
>   Blocking target when backup is running, unblock it.
> 
> - mirror_complete
> 
>   Blocking s->to_replace until mirror_exit, OK.
> 
> - block_job_complete
> 
>   The block job may be long running. Unblock it.
> 
> - init_blk_migration
> 
>   The block migration may be long running, Unblock it.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  blockjob.c                      | 1 +
>  hw/block/dataplane/virtio-blk.c | 1 +
>  hw/scsi/virtio-scsi.c           | 1 +
>  include/block/block.h           | 1 +
>  migration/block.c               | 1 +
>  5 files changed, 5 insertions(+)
> 
> diff --git a/blockjob.c b/blockjob.c
> index 2755465..e39bdde 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -51,6 +51,7 @@ void *block_job_create(const BlockJobDriver *driver, BlockDriverState *bs,
>                 BlockJobType_lookup[driver->job_type]);
>      bdrv_op_block_all(bs, job->blocker);
>      bdrv_op_unblock(bs, BLOCK_OP_TYPE_DATAPLANE, job->blocker);
> +    bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, job->blocker);
>  
>      job->driver        = driver;
>      job->bs            = bs;
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 3db139b..3ecc8bd 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -209,6 +209,7 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_MIRROR, s->blocker);
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_STREAM, s->blocker);
>      blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_REPLACE, s->blocker);
> +    blk_op_unblock(conf->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
>  
>      *dataplane = s;
>  }
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index e242fef..5e15fa6 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -772,6 +772,7 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
>              return;
>          }
>          blk_op_block_all(sd->conf.blk, s->blocker);
> +        blk_op_unblock(sd->conf.blk, BLOCK_OP_TYPE_DEVICE_IO, s->blocker);
>          aio_context_acquire(s->ctx);
>          blk_set_aio_context(sd->conf.blk, s->ctx);
>          aio_context_release(s->ctx);
> diff --git a/include/block/block.h b/include/block/block.h
> index 7d1a717..906fb31 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -159,6 +159,7 @@ typedef enum BlockOpType {
>      BLOCK_OP_TYPE_RESIZE,
>      BLOCK_OP_TYPE_STREAM,
>      BLOCK_OP_TYPE_REPLACE,
> +    BLOCK_OP_TYPE_DEVICE_IO,
>      BLOCK_OP_TYPE_MAX,
>  } BlockOpType;
>  
> diff --git a/migration/block.c b/migration/block.c
> index ddb59cc..b833bac 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -379,6 +379,7 @@ static void init_blk_migration(QEMUFile *f)
>          alloc_aio_bitmap(bmds);
>          error_setg(&bmds->blocker, "block device is in use by migration");
>          bdrv_op_block_all(bs, bmds->blocker);
> +        bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, bmds->blocker);
>          bdrv_ref(bs);
>  
>          block_mig_state.total_sector_sum += sectors;
> 

Re: [Qemu-devel] [PATCH v3 12/12] virtio-scsi-dataplane: Add "device IO" op blocker listener

[Paolo Bonzini]

On 15/05/2015 08:04, Fam Zheng wrote:
> @@ -111,6 +111,10 @@ static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
>      VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
>      VirtIOSCSIReq *req;
>  
> +    if (s->pause_counter) {
> +        virtio_scsi_stop_ioeventfd(s);
> +        return;
> +    }
>      event_notifier_test_and_clear(notifier);
>      while ((req = virtio_scsi_pop_req_vring(s, vring))) {
>          virtio_scsi_handle_ctrl_req(s, req);
> @@ -124,6 +128,10 @@ static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
>      VirtIOSCSI *s = vring->parent;
>      VirtIODevice *vdev = VIRTIO_DEVICE(s);
>  
> +    if (s->pause_counter) {
> +        virtio_scsi_stop_ioeventfd(s);
> +        return;
> +    }
>      event_notifier_test_and_clear(notifier);
>  
>      if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {

Why are these needed?

Paolo

Re: [Qemu-devel] [PATCH v3 12/12] virtio-scsi-dataplane: Add "device IO" op blocker listener

[Fam Zheng]

On Fri, 05/15 08:50, Paolo Bonzini wrote:
> 
> 
> On 15/05/2015 08:04, Fam Zheng wrote:
> > @@ -111,6 +111,10 @@ static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
> >      VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
> >      VirtIOSCSIReq *req;
> >  
> > +    if (s->pause_counter) {
> > +        virtio_scsi_stop_ioeventfd(s);
> > +        return;
> > +    }
> >      event_notifier_test_and_clear(notifier);
> >      while ((req = virtio_scsi_pop_req_vring(s, vring))) {
> >          virtio_scsi_handle_ctrl_req(s, req);
> > @@ -124,6 +128,10 @@ static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
> >      VirtIOSCSI *s = vring->parent;
> >      VirtIODevice *vdev = VIRTIO_DEVICE(s);
> >  
> > +    if (s->pause_counter) {
> > +        virtio_scsi_stop_ioeventfd(s);
> > +        return;
> > +    }
> >      event_notifier_test_and_clear(notifier);
> >  
> >      if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
> 
> Why are these needed?

Not strictly. I think it's something like an "assert(!s->pause_counter)" but
said gently.

Fam

Re: [Qemu-devel] [PATCH v3 01/12] block: Add op blocker type "device IO"

[Fam Zheng]

On Fri, 05/15 14:22, Wen Congyang wrote:
> On 05/15/2015 02:04 PM, Fam Zheng wrote:
> > It blocks device IO.
> 
> I am reading mirror codes recently, and have a question:
> When block job mirror is finished, the source and target is synced. But we
> call bdrv_swap() later(in bh context). Can the guest write something to
> the source before the bh is scheduled? If the answer is yes, I think
> we should use this to block the guest's disk I/O.

I think you're right. After mirror_run returns, anything can happen on this aio
context, including guest writing.

Fam

Re: [Qemu-devel] [PATCH v3 12/12] virtio-scsi-dataplane: Add "device IO" op blocker listener

[Paolo Bonzini]

On 15/05/2015 09:03, Fam Zheng wrote:
> On Fri, 05/15 08:50, Paolo Bonzini wrote:
>>
>>
>> On 15/05/2015 08:04, Fam Zheng wrote:
>>> @@ -111,6 +111,10 @@ static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
>>>      VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
>>>      VirtIOSCSIReq *req;
>>>  
>>> +    if (s->pause_counter) {
>>> +        virtio_scsi_stop_ioeventfd(s);
>>> +        return;
>>> +    }
>>>      event_notifier_test_and_clear(notifier);
>>>      while ((req = virtio_scsi_pop_req_vring(s, vring))) {
>>>          virtio_scsi_handle_ctrl_req(s, req);
>>> @@ -124,6 +128,10 @@ static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
>>>      VirtIOSCSI *s = vring->parent;
>>>      VirtIODevice *vdev = VIRTIO_DEVICE(s);
>>>  
>>> +    if (s->pause_counter) {
>>> +        virtio_scsi_stop_ioeventfd(s);
>>> +        return;
>>> +    }
>>>      event_notifier_test_and_clear(notifier);
>>>  
>>>      if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
>>
>> Why are these needed?
> 
> Not strictly. I think it's something like an "assert(!s->pause_counter)" but
> said gently.

Why be gentle? :)

Paolo

Re: [Qemu-devel] [PATCH v3 12/12] virtio-scsi-dataplane: Add "device IO" op blocker listener

[Fam Zheng]

On Fri, 05/15 09:26, Paolo Bonzini wrote:
> 
> 
> On 15/05/2015 09:03, Fam Zheng wrote:
> > On Fri, 05/15 08:50, Paolo Bonzini wrote:
> >>
> >>
> >> On 15/05/2015 08:04, Fam Zheng wrote:
> >>> @@ -111,6 +111,10 @@ static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
> >>>      VirtIOSCSI *s = VIRTIO_SCSI(vring->parent);
> >>>      VirtIOSCSIReq *req;
> >>>  
> >>> +    if (s->pause_counter) {
> >>> +        virtio_scsi_stop_ioeventfd(s);
> >>> +        return;
> >>> +    }
> >>>      event_notifier_test_and_clear(notifier);
> >>>      while ((req = virtio_scsi_pop_req_vring(s, vring))) {
> >>>          virtio_scsi_handle_ctrl_req(s, req);
> >>> @@ -124,6 +128,10 @@ static void virtio_scsi_iothread_handle_event(EventNotifier *notifier)
> >>>      VirtIOSCSI *s = vring->parent;
> >>>      VirtIODevice *vdev = VIRTIO_DEVICE(s);
> >>>  
> >>> +    if (s->pause_counter) {
> >>> +        virtio_scsi_stop_ioeventfd(s);
> >>> +        return;
> >>> +    }
> >>>      event_notifier_test_and_clear(notifier);
> >>>  
> >>>      if (!(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) {
> >>
> >> Why are these needed?
> > 
> > Not strictly. I think it's something like an "assert(!s->pause_counter)" but
> > said gently.
> 
> Why be gentle? :)

I guess because I want to be a gentleman.. :)

But since being gentle to these two won't make me a fortune to become a
gentlemen, let's just assert!

Fam

Re: [Qemu-devel] [PATCH v3 02/12] block: Add op blocker notifier list

[Max Reitz]

On 15.05.2015 08:04, Fam Zheng wrote:
> BDS users can register a notifier and get notified about op blocker
> changes.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   block.c                   | 35 +++++++++++++++++++++++++++++++++++
>   include/block/block.h     |  8 ++++++++
>   include/block/block_int.h |  3 +++
>   3 files changed, 46 insertions(+)
>
> diff --git a/block.c b/block.c
> index 7904098..178e186 100644
> --- a/block.c
> +++ b/block.c
> @@ -3375,6 +3375,19 @@ struct BdrvOpBlocker {
>       QLIST_ENTRY(BdrvOpBlocker) list;
>   };
>   
> +/* Add a notifier which will be notified when the first blocker of some type is
> + * added to bs, or when the last blocker is removed. The notifier handler
> + * should receive a BlockOpEvent data.
> + *
> + * Caller must hold bs->aio_context; the notifier handler is also called with
> + * it hold.

*held (I think)

With that fixed:

Reviewed-by: Max Reitz <mreitz@redhat.com>

(Although I'm missing a place where the notifiers are freed (on 
bdrv_delete()/bdrv_close()), but maybe that's done in a different patch)

> + */
> +void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
> +                                  Notifier *notifier)
> +{
> +    notifier_list_add(&bs->op_blocker_notifiers, notifier);
> +}
> +
>   bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
>   {
>       BdrvOpBlocker *blocker;
> @@ -3391,26 +3404,48 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
>       return false;
>   }
>   
> +static void bdrv_op_blocker_notify(BlockDriverState *bs, BlockOpType op,
> +                                   Error *reason, bool blocking)
> +{
> +    BlockOpEvent event = (BlockOpEvent) {
> +        op = op,
> +        reason = reason,
> +        blocking = blocking,
> +    };
> +
> +    notifier_list_notify(&bs->op_blocker_notifiers, &event);
> +}
> +
>   void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
>   {
> +    bool blocked;
>       BdrvOpBlocker *blocker;
>       assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
>   
>       blocker = g_new0(BdrvOpBlocker, 1);
>       blocker->reason = reason;
> +    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
>       QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
> +    if (!blocked) {
> +        bdrv_op_blocker_notify(bs, op, reason, true);
> +    }
>   }
>   
>   void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
>   {
> +    bool blocked;
>       BdrvOpBlocker *blocker, *next;
>       assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> +    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
>       QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
>           if (blocker->reason == reason) {
>               QLIST_REMOVE(blocker, list);
>               g_free(blocker);
>           }
>       }
> +    if (blocked && QLIST_EMPTY(&bs->op_blockers[op])) {
> +        bdrv_op_blocker_notify(bs, op, reason, false);
> +    }
>   }
>   
>   void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
> diff --git a/include/block/block.h b/include/block/block.h
> index 906fb31..3420b2c 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -163,6 +163,12 @@ typedef enum BlockOpType {
>       BLOCK_OP_TYPE_MAX,
>   } BlockOpType;
>   
> +typedef struct {
> +    BlockOpType type;
> +    Error *reason;
> +    bool blocking;
> +} BlockOpEvent;
> +
>   void bdrv_iostatus_enable(BlockDriverState *bs);
>   void bdrv_iostatus_reset(BlockDriverState *bs);
>   void bdrv_iostatus_disable(BlockDriverState *bs);
> @@ -491,6 +497,8 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
>   void bdrv_ref(BlockDriverState *bs);
>   void bdrv_unref(BlockDriverState *bs);
>   
> +void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
> +                                  Notifier *notifier);
>   bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
>   void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);
>   void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index db29b74..29d1c84 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -418,6 +418,9 @@ struct BlockDriverState {
>       /* operation blockers */
>       QLIST_HEAD(, BdrvOpBlocker) op_blockers[BLOCK_OP_TYPE_MAX];
>   
> +    /* Callback when one list in op_blockers has "empty" status change. */
> +    NotifierList op_blocker_notifiers;
> +
>       /* long-running background operation */
>       BlockJob *job;
>   

Re: [Qemu-devel] [PATCH v3 03/12] block-backend: Add blk_op_blocker_add_notifier

[Max Reitz]

On 15.05.2015 08:04, Fam Zheng wrote:
> Forward the call to bdrv_op_blocker_add_notifier.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   block/block-backend.c          | 6 ++++++
>   include/sysemu/block-backend.h | 2 ++
>   2 files changed, 8 insertions(+)

Reviewed-by: Max Reitz <mreitz@redhat.com>

Re: [Qemu-devel] [PATCH v3 04/12] virtio-blk: Move complete_request to 'ops' structure

[Max Reitz]

On 15.05.2015 08:04, Fam Zheng wrote:
> Should more ops be added to differentiate code between dataplane and
> non-dataplane, the new saved_ops approach will be cleaner than messing
> with N pointers.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   hw/block/dataplane/virtio-blk.c | 13 ++++++++-----
>   hw/block/virtio-blk.c           |  8 ++++++--
>   include/hw/virtio/virtio-blk.h  |  9 +++++++--
>   3 files changed, 21 insertions(+), 9 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>

Re: [Qemu-devel] [PATCH v3 05/12] virtio-blk: Don't handle output when there is "device IO" op blocker

[Max Reitz]

On 15.05.2015 08:04, Fam Zheng wrote:
> virtio-blk now listens to op blocker change of the associated block
> backend.
>
> Up on setting op blocker on BLOCK_OP_TYPE_DEVICE_IO:
>
>    non-dataplane:
>     1) Set VirtIOBlock.paused
>     2) In virtio_blk_handle_output, do nothing if VirtIOBlock.paused
>
>    dataplane:
>     1) Clear the host event notifier
>     2) In handle_notify, do nothing if VirtIOBlock.paused
>
> Up on removing the op blocker:
>
>    non-dataplane:
>     1) Clear VirtIOBlock.paused
>     2) Schedule a BH on the AioContext of the backend, which calls
>     virtio_blk_handle_output, so that the previous unhandled kicks can
>     make progress
>
>    dataplane:
>     1) Set the host event notifier
>     2) Notify the host event notifier so that unhandled events are
>     processed
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   hw/block/dataplane/virtio-blk.c | 25 +++++++++++++++-
>   hw/block/virtio-blk.c           | 63 +++++++++++++++++++++++++++++++++++++++--
>   include/hw/virtio/virtio-blk.h  |  8 +++++-
>   3 files changed, 92 insertions(+), 4 deletions(-)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index e287e09..a5e8e35 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -87,8 +87,28 @@ static void complete_request_vring(VirtIOBlockReq *req, unsigned char status)
>       qemu_bh_schedule(s->bh);
>   }
>   
> +static void virtio_blk_data_plane_pause(VirtIOBlock *vblk)
> +{
> +    VirtIOBlockDataPlane *s = vblk->dataplane;
> +
> +    event_notifier_test_and_clear(&s->host_notifier);
> +    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
> +}
> +
> +static void handle_notify(EventNotifier *e);
> +static void virtio_blk_data_plane_resume(VirtIOBlock *vblk)
> +{
> +    VirtIOBlockDataPlane *s = vblk->dataplane;
> +
> +    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
> +
> +    event_notifier_set(&s->host_notifier);
> +}
> +
>   static const VirtIOBlockOps virtio_blk_data_plane_ops = {
> -    .complete_request = complete_request_vring,
> +    .complete_request           = complete_request_vring,
> +    .pause                      = virtio_blk_data_plane_pause,
> +    .resume                     = virtio_blk_data_plane_resume,
>   };
>   
>   static void handle_notify(EventNotifier *e)
> @@ -98,6 +118,9 @@ static void handle_notify(EventNotifier *e)
>       VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
>   
>       event_notifier_test_and_clear(&s->host_notifier);
> +    if (vblk->paused) {
> +        return;
> +    }
>       blk_io_plug(s->conf->conf.blk);
>       for (;;) {
>           MultiReqBuffer mrb = {};
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index f4a9d19..4bc1b2a 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -59,8 +59,38 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
>       virtio_notify(vdev, s->vq);
>   }
>   
> +typedef struct {
> +    QEMUBH *bh;
> +    VirtIOBlock *s;
> +} VirtIOBlockResumeData;
> +
> +static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq);
> +static void virtio_blk_resume_bh_cb(void *opaque)
> +{
> +    VirtIOBlockResumeData *data = opaque;
> +    qemu_bh_delete(data->bh);
> +    virtio_blk_handle_output(VIRTIO_DEVICE(data->s), data->s->vq);
> +}
> +
> +static void virtio_blk_pause(VirtIOBlock *vblk)
> +{
> +    /* TODO: stop ioeventfd */
> +}
> +
> +static void virtio_blk_resume(VirtIOBlock *vblk)
> +{
> +    VirtIOBlockResumeData *data = g_new(VirtIOBlockResumeData, 1);
> +    data->bh = aio_bh_new(blk_get_aio_context(vblk->blk),
> +            virtio_blk_resume_bh_cb, data);
> +    data->s = vblk;
> +    data->s->paused = false;
> +    qemu_bh_schedule(data->bh);
> +}
> +
>   static const VirtIOBlockOps virtio_blk_ops = (VirtIOBlockOps) {
> -    .complete_request = virtio_blk_complete_request,
> +    .complete_request           = virtio_blk_complete_request,
> +    .pause                      = virtio_blk_pause,
> +    .resume                     = virtio_blk_resume,
>   };
>   
>   static void virtio_blk_req_complete(VirtIOBlockReq *req, unsigned char status)
> @@ -597,6 +627,9 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>       VirtIOBlockReq *req;
>       MultiReqBuffer mrb = {};
>   
> +    if (s->paused) {
> +        return;
> +    }
>       /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
>        * dataplane here instead of waiting for .set_status().
>        */
> @@ -787,7 +820,7 @@ static void virtio_blk_save(QEMUFile *f, void *opaque)
>   
>       virtio_save(vdev, f);
>   }
> -
> +
>   static void virtio_blk_save_device(VirtIODevice *vdev, QEMUFile *f)
>   {
>       VirtIOBlock *s = VIRTIO_BLK(vdev);
> @@ -875,6 +908,29 @@ static void virtio_blk_migration_state_changed(Notifier *notifier, void *data)
>       }
>   }
>   
> +static void virtio_blk_op_blocker_changed(Notifier *notifier, void *opaque)
> +{
> +    BlockOpEvent *event = opaque;
> +    VirtIOBlock *s = container_of(notifier, VirtIOBlock,
> +                                  op_blocker_notifier);
> +    bool pause;
> +
> +    if (event->type != BLOCK_OP_TYPE_DEVICE_IO) {
> +        return;
> +    }
> +    pause = event->blocking || blk_op_is_blocked(s->blk,
> +                                                    BLOCK_OP_TYPE_DEVICE_IO,
> +                                                    NULL);

Indentation is off if you intended to indent based on the opening 
parenthesis.

Different question: Since event->type == BLOCK_OP_TYPE_DEVICE_IO, when 
will event->blocking ever be not equal to blk_op_is_blocked()?

> +    if (pause == s->paused) {
> +        return;
> +    }
> +    if (pause) {
> +        s->ops->pause(s);
> +    } else {
> +        s->ops->resume(s);
> +    }
> +}
> +
>   static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
>   {
>       VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> @@ -926,6 +982,9 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
>       blk_set_guest_block_size(s->blk, s->conf.conf.logical_block_size);
>   
>       blk_iostatus_enable(s->blk);
> +
> +    s->op_blocker_notifier.notify = virtio_blk_op_blocker_changed;
> +    blk_op_blocker_add_notifier(s->blk, &s->op_blocker_notifier);

This is indeed a way to make sure the notifier is not leaked. *cough* I 
don't know why I never think of that...

Apart from the event->blocking question above, looks good to me 
(although that's a pretty weak statement, considering I don't know the 
virtio code that well...).

Max

>   }
>   
>   static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
> diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> index 28b3436..aa15fea 100644
> --- a/include/hw/virtio/virtio-blk.h
> +++ b/include/hw/virtio/virtio-blk.h
> @@ -42,12 +42,16 @@ struct VirtIOBlkConf
>   };
>   
>   struct VirtIOBlockDataPlane;
> -
> +struct VirtIOBlock;
>   struct VirtIOBlockReq;
>   
>   typedef struct {
>       /* Function to push to vq and notify guest */
>       void (*complete_request)(struct VirtIOBlockReq *req, unsigned char status);
> +
> +    /* Functions to pause/resume request handling */
> +    void (*pause)(struct VirtIOBlock *vblk);
> +    void (*resume)(struct VirtIOBlock *vblk);
>   } VirtIOBlockOps;
>   
>   typedef struct VirtIOBlock {
> @@ -62,6 +66,8 @@ typedef struct VirtIOBlock {
>       VMChangeStateEntry *change;
>       const VirtIOBlockOps *ops;
>       Notifier migration_state_notifier;
> +    Notifier op_blocker_notifier;
> +    bool paused;
>       struct VirtIOBlockDataPlane *dataplane;
>   } VirtIOBlock;
>   

Re: [Qemu-devel] [PATCH v3 06/12] nbd-server: Clear "can_read" when "device io" blocker is set

[Max Reitz]

On 15.05.2015 08:04, Fam Zheng wrote:
> So that NBD export cannot submit IO during bdrv_drain_all().
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   nbd.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)

But can_read is not cleared until nbd_update_can_read() is called, which 
is only in nbd_request_get(), nbd_request_put(), and 
nbd_co_receive_request(), which are all called from nbd_trip() - so the 
one request which clears can_read will most probably be itself processed.

Maybe we should call nbd_update_can_read() in nbd_op_blocker_changed(), 
for all clients of the export? Or just once somewhere at the beginning 
of processing a request, and if io_blocked is set, just yield...

Max

Re: [Qemu-devel] [PATCH v3 06/12] nbd-server: Clear "can_read" when "device io" blocker is set

[Fam Zheng]

On Mon, 05/18 20:35, Max Reitz wrote:
> On 15.05.2015 08:04, Fam Zheng wrote:
> >So that NBD export cannot submit IO during bdrv_drain_all().
> >
> >Signed-off-by: Fam Zheng <famz@redhat.com>
> >---
> >  nbd.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> 
> But can_read is not cleared until nbd_update_can_read() is called, which is
> only in nbd_request_get(), nbd_request_put(), and nbd_co_receive_request(),
> which are all called from nbd_trip() - so the one request which clears
> can_read will most probably be itself processed.
> 
> Maybe we should call nbd_update_can_read() in nbd_op_blocker_changed(), for
> all clients of the export? Or just once somewhere at the beginning of
> processing a request, and if io_blocked is set, just yield...

I think you're right. I'll fix that.

Fam

Re: [Qemu-devel] [PATCH v3 05/12] virtio-blk: Don't handle output when there is "device IO" op blocker

[Fam Zheng]

On Mon, 05/18 20:19, Max Reitz wrote:
> On 15.05.2015 08:04, Fam Zheng wrote:
> 
> Indentation is off if you intended to indent based on the opening
> parenthesis.

Will fix.

> 
> Different question: Since event->type == BLOCK_OP_TYPE_DEVICE_IO, when will
> event->blocking ever be not equal to blk_op_is_blocked()?

It's unnecessary.

Fam