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xen-block: implement BlockDevOps->drained_begin()

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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 <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-12-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-05-16 15:02:29 -04:00 • committed by Kevin Wolf
parent ab61335025
commit f6eac904f6
4 changed files with 59 additions and 16 deletions
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7
hw/xen/xen-bus.c
View file

@ -846,8 +846,11 @@ void xen_device_set_event_channel_context(XenDevice *xendev,
NULL, NULL, NULL, NULL, NULL);
channel->ctx = ctx;
aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh), true,
xen_device_event, NULL, xen_device_poll, NULL, channel);
if (ctx) {
aio_set_fd_handler(channel->ctx, qemu_xen_evtchn_fd(channel->xeh),
true, xen_device_event, NULL, xen_device_poll, NULL,
channel);
}
}
XenEventChannel *xen_device_bind_event_channel(XenDevice *xendev,