During the review of the dataplane code, the EventPoll API morphed itself
(not concidentially) into something very very similar to an AioContext.
Thus, it is trivial to convert virtio-blk-dataplane to use AioContext,
and a first baby step towards letting dataplane talk directly to the
QEMU block layer.
The only interesting note is the value-copy of EventNotifiers. At least
in my opinion this is part of the EventNotifier API and is even portable
to Windows. Of course, in this case you should not close the notifier's
underlying file descriptors or handle with event_notifier_cleanup.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
When dataplane is stopping, the s->vdev->binding->set_host_notifier(...,
false) call can invoke the virtqueue handler if an ioeventfd
notification is pending. This causes hw/virtio-blk.c to invoke
virtio_blk_data_plane_start() before virtio_blk_data_plane_stop()
returns!
The result is that we try to restart dataplane while trying to stop it
and the following assertion is raised:
msix_set_mask_notifier: Assertion `!dev->msix_mask_notifier' failed.
Although the code was intended to prevent this scenario, the s->started
boolean isn't enough. Add s->stopping so that we can postpone clearing
s->started until we've completely stopped dataplane.
This way, virtqueue handler calls during virtio_blk_data_plane_stop()
are ignored. When dataplane is legitimately started again later we
already self-kick ourselves to resume processing.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
virtio_pci_set_guest_notifiers() now takes an additional argument to
specify the number of virtqueues to assign a guest notifier for. This
causes a build breakage for CONFIG_VIRTIO_BLK_DATA_PLANE builds:
/home/mdroth/w/qemu2.git/hw/dataplane/virtio-blk.c: In function
‘virtio_blk_data_plane_start’:
/home/mdroth/w/qemu2.git/hw/dataplane/virtio-blk.c:451:47: error: too
few arguments to function ‘s->vdev->binding->set_guest_notifiers’
/home/mdroth/w/qemu2.git/hw/dataplane/virtio-blk.c: In function
‘virtio_blk_data_plane_stop’:
/home/mdroth/w/qemu2.git/hw/dataplane/virtio-blk.c:511:5: error: too few
arguments to function ‘s->vdev->binding->set_guest_notifiers’
make[1]: *** [hw/dataplane/virtio-blk.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [subdir-x86_64-softmmu] Error 2
Fix this by passing 1 as the number of virtqueues to assign notifiers
for.
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
O_DIRECT on Linux has alignment requirements on I/O buffers and
misaligned requests result in -EINVAL. The Linux virtio_blk guest
driver usually submits aligned requests so I forgot to handle misaligned
requests.
It turns out that virtio-win guest drivers submit misaligned requests.
Handle them using a bounce buffer that meets alignment requirements.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Extract code for read/write command processing into do_rdwr_cmd(). This
brings together pieces that are spread across process_request().
The real motivation is to set the stage for handling misaligned
requests, which the next patch tackles.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
virtio-blk-data-plane is a subset implementation of virtio-blk. It only
handles read, write, and flush requests. It does this using a dedicated
thread that executes an epoll(2)-based event loop and processes I/O
using Linux AIO.
This approach performs very well but can be used for raw image files
only. The number of IOPS achieved has been reported to be several times
higher than the existing virtio-blk implementation.
Eventually it should be possible to unify virtio-blk-data-plane with the
main body of QEMU code once the block layer and hardware emulation is
able to run outside the global mutex.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
