[PATCH v2 RFC 0/3] virtio: add new notify() callback to virtio_driver

[Heinz Graalfs <graalfs@linux.vnet.ibm.com>]

Hi, here is an updated patch-set with changes as suggested by Michael Tsirkin.

When an active virtio block device is hot-unplugged from a KVM guest, running
affected guest user applications are not aware of any errors that occur due
to the lost device. This patch-set adds code to avoid further request queueing
when a lost block device is detected, resulting in appropriate error info.

On System z there exists no handshake mechanism between host and guest
when a device is hot-unplugged. The device is removed and no further I/O
is possible.

When an online channel device disappears on System z the kernel's CIO layer
informs the driver (virtio_ccw) about the lost device.

It's just the block device drivers that care to provide a notify
callback.

Here are some more error details:

For a particular block device virtio's request function virtblk_request()
is called by the block layer to queue requests to be handled by the host.
In case of a lost device requests can still be queued, but an appropriate
subsequent host kick usually fails. This leads to situations where no error
feedback is shown.

In order to prevent request queueing for lost devices appropriate settings
in the block layer should be made. Exploiting System z's CIO notify handler
callback, and adding a corresponding new virtio_driver notify() handler to
'inform' the block layer, solve this task.


v1->v2 changes:
 - add include of linux/notifier.h (I also added it to the 3rd patch)
 - get queue lock in order to be able to use safe queue_flag_set() functions
   in virtblk_notify() handler


Patch 1 adds an optional notify() callback to virtio_driver.

Patch 2 adds a new notify() callback for the virtio_blk driver. When called
for a lost device settings are made to prevent future request queueing.

Patch 3 modifies the CIO notify handler in virtio_ccw's transport layer to pass
on the lost device info to virtio's backend driver virtio_blk.

Heinz Graalfs (3):
  virtio: add notify() callback to virtio_driver
  virtio_blk: add virtblk_notify() as virtio_driver's notify() callback
  virtio_ccw: invoke virtio_driver's notify() on CIO_GONE notification

 drivers/block/virtio_blk.c    | 17 +++++++++++++++++
 drivers/s390/kvm/virtio_ccw.c | 15 +++++++++++++--
 drivers/virtio/virtio.c       |  9 +++++++++
 include/linux/virtio.h        | 10 ++++++++++
 4 files changed, 49 insertions(+), 2 deletions(-)

-- 
1.8.3.1