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

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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), it would be confusing, and I'm not sure how you could extend
> the during_flush machinery.

vhost_scsi_flush() is called under the vs->dev.mutex lock.

> What about making vhost_scsi_flush() wait for all pending requests,
> including those issues during the flush operation?

This will take unbonded time if guest keep sending requests.

> Then you can easily
> support concurrent flushes; just add a waitqueue and wake_up_all at the
> end of the flush operation.

I am not sure why we want concurrent flushes. The flush thing is
already getting complex.

> BTW, adding such a ioctl as part of this patch would probably be a good
> thing to do anyway.
> 
> Paolo

-- 
Asias
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