Re: [PATCH 1/2] tcm_vhost: Wait for pending requests in vhost_scsi_flush()

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/03/2013 12:53, Michael S. Tsirkin ha scritto:
> On Mon, Mar 11, 2013 at 12:36:37PM +0100, Paolo Bonzini wrote:
>> Il 11/03/2013 06:09, Asias He ha scritto:
>>> This patch makes vhost_scsi_flush() wait for all the pending requests
>>> issued before the flush operation to be finished.
>>
>> There is no protection against issuing concurrent flush operations.  If
>> we later would like to make the flush a ioctl (for example for migration
>> purposes),
> 
> For migration I think we need to stop vhost, flush isn't useful
> if we keep submitting requests afterwards.

This ioctl would run when the vm is stopped.

Paolo

>> it would be confusing, and I'm not sure how you could extend
>> the during_flush machinery.
>>
>> What about making vhost_scsi_flush() wait for all pending requests,
>> including those issues during the flush operation?  Then you can easily
>> support concurrent flushes; just add a waitqueue and wake_up_all at the
>> end of the flush operation.
>>
>> BTW, adding such a ioctl as part of this patch would probably be a good
>> thing to do anyway.
> 
> Please keep it separate, it's painful enough that we have a driver
> with to established userspace, I don't want to add ioctls
> until it's used by some upstream.
>