[09/13] hw/xen: do not set is_external=true on evtchn fds

Commit Message

Stefan Hajnoczi April 3, 2023, 6:30 p.m. UTC

is_external=true suspends fd handlers between aio_disable_external() and
aio_enable_external(). The block layer's drain operation uses this
mechanism to prevent new I/O from sneaking in between
bdrv_drained_begin() and bdrv_drained_end().

The xen-block device actually works fine with is_external=false because
BlockBackend requests are already queued between bdrv_drained_begin()
and bdrv_drained_end(). Since the Xen ring size is finite, request
queuing will stop once the ring is full and memory usage is bounded.
After bdrv_drained_end() the BlockBackend requests will resume and
xen-block's processing will continue.

This is part of ongoing work to remove the aio_disable_external() API.

Signed-off-by: Stefan Hajnoczi <[e-mail]>
---
 hw/xen/xen-bus.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Patch

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index c59850b1de..c4fd26abe1 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -842,11 +842,11 @@  void xen_device_set_event_channel_context(XenDevice *xendev,
     }
 
     if (channel->ctx)
-        aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), true,
+        aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), false,
                            NULL, NULL, NULL, NULL, NULL);
 
     channel->ctx = ctx;
-    aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), true,
+    aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), false,
                        xen_device_event, NULL, xen_device_poll, NULL, channel);
 }
 
@@ -920,7 +920,7 @@  void xen_device_unbind_event_channel(XenDevice *xendev,
 
     QLIST_REMOVE(channel, list);
 
-    aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), true,
+    aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), false,
                        NULL, NULL, NULL, NULL, NULL);
 
     if (qemu_xen_evtchn_unbind(channel->xeh, channel->local_port) < 0) {