Detach event channels during drained sections to stop I/O submission
from the ring. xen-block is no longer reliant on aio_disable_external()
after this patch. This will allow us to remove the
aio_disable_external() API once all other code that relies on it is
converted.
Extend xen_device_set_event_channel_context() to allow ctx=NULL. The
event channel still exists but the event loop does not monitor the file
descriptor. Event channel processing can resume by calling
xen_device_set_event_channel_context() with a non-NULL ctx.
Factor out xen_device_set_event_channel_context() calls in
hw/block/dataplane/xen-block.c into attach/detach helper functions.
Incidentally, these don't require the AioContext lock because
aio_set_fd_handler() is thread-safe.
It's safer to register BlockDevOps after the dataplane instance has been
created. The BlockDevOps .drained_begin/end() callbacks depend on the
dataplane instance, so move the blk_set_dev_ops() call after
xen_block_dataplane_create().
Signed-off-by: Stefan Hajnoczi
---
hw/block/dataplane/xen-block.h | 2 ++
hw/block/dataplane/xen-block.c | 42 +-
hw/block/xen-block.c | 24 ---
hw/xen/xen-bus.c | 7 --
4 files changed, 59 insertions(+), 16 deletions(-)
diff --git a/hw/block/dataplane/xen-block.h b/hw/block/dataplane/xen-block.h
index 76dcd51c3d..7b8e9df09f 100644
--- a/hw/block/dataplane/xen-block.h
+++ b/hw/block/dataplane/xen-block.h
@@ -26,5 +26,7 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
unsigned int protocol,
Error **errp);
void xen_block_dataplane_stop(XenBlockDataPlane *dataplane);
+void xen_block_dataplane_attach(XenBlockDataPlane *dataplane);
+void xen_block_dataplane_detach(XenBlockDataPlane *dataplane);
#endif /* HW_BLOCK_DATAPLANE_XEN_BLOCK_H */
diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index d8bc39d359..2597f38805 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -664,6 +664,30 @@ void xen_block_dataplane_destroy(XenBlockDataPlane
*dataplane)
g_free(dataplane);
}
+void xen_block_dataplane_detach(XenBlockDataPlane *dataplane)
+{
+if (!dataplane || !dataplane->event_channel) {
+return;
+}
+
+/* Only reason for failure is a NULL channel */
+xen_device_set_event_channel_context(dataplane->xendev,
+ dataplane->event_channel,
+ NULL, _abort);
+}
+
+void xen_block_dataplane_attach(XenBlockDataPlane *dataplane)
+{
+if (!dataplane || !dataplane->event_channel) {
+return;
+}
+
+/* Only reason for failure is a NULL channel */
+xen_device_set_event_channel_context(dataplane->xendev,
+ dataplane->event_channel,
+ dataplane->ctx, _abort);
+}
+
void xen_block_dataplane_stop(XenBlockDataPlane *dataplane)
{
XenDevice *xendev;
@@ -674,13 +698,11 @@ void xen_block_dataplane_stop(XenBlockDataPlane
*dataplane)
xendev = dataplane->xendev;
-aio_context_acquire(dataplane->ctx);
-if (dataplane->event_channel) {
-/* Only reason for failure is a NULL channel */
-xen_device_set_event_channel_context(xendev, dataplane->event_channel,
- qemu_get_aio_context(),
- _abort);
+if (!blk_in_drain(dataplane->blk)) {
+xen_block_dataplane_detach(dataplane);
}
+
+aio_context_acquire(dataplane->ctx);
/* Xen doesn't have multiple users for nodes, so this can't fail */
blk_set_aio_context(dataplane->blk, qemu_get_aio_context(), _abort);
aio_context_release(dataplane->ctx);
@@ -819,11 +841,9 @@ void xen_block_dataplane_start(XenBlockDataPlane
*dataplane,
blk_set_aio_context(dataplane->blk, dataplane->ctx, NULL);
aio_context_release(old_context);
-/* Only reason for failure is a NULL channel */
-aio_context_acquire(dataplane->ctx);
-xen_device_set_event_channel_context(xendev, dataplane->event_channel,
- dataplane->ctx, _abort);
-aio_context_release(dataplane->ctx);
+if (!blk_in_drain(dataplane->blk)) {
+xen_block_dataplane_attach(dataplane);
+}
return;
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index f5a744589d..f099914831 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -189,8 +189,26 @@ static void xen_block_resize_cb(void *opaque)
xen_device_backend_printf(xendev, "state", "%u", state);
}
+/* Suspend request handling */
+static void xen_block_drained_begin(void *opaque)
+{
+XenBlockDevice *blockdev = opaque;
+
+xen_block_dataplane_detach(blockdev->dataplane);
+}
+
+/* Resume request handling */
+static void xen_block_drained_end(void *opaque)
