Re: [PATCH V3 11/11] vhost: allow userspace to create workers

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On Tue, Oct 26, 2021 at 11:49:37AM -0500, michael.christie@xxxxxxxxxx wrote:
> On 10/26/21 12:37 AM, Jason Wang wrote:
> > Do we need VHOST_VRING_FREE_WORKER? And I wonder if using dedicated ioctls are better:
> > 
> > VHOST_VRING_NEW/FREE_WORKER
> > VHOST_VRING_ATTACH_WORKER
> 
> 
> We didn't need a free worker, because the kernel handles it for userspace. I
> tried to make it easy for userspace because in some cases it may not be able
> to do syscalls like close on the device. For example if qemu crashes or for
> vhost-scsi we don't do an explicit close during VM shutdown.
> 
> So we start off with the default worker thread that's used by all vqs like we do
> today. Userspace can then override it by creating a new worker. That also unbinds/
> detaches the existing worker and does a put on the workers refcount. We also do a
> put on the worker when we stop using it during device shutdown/closure/release.
> When the worker's refcount goes to zero the kernel deletes it.

Please document the worker (p)id lifetime for the ioctl. Otherwise
userspace doesn't know whether a previously created worker is still
alive.

SSTefan

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