Re: [PATCH v2] virtio-rng: return available data with O_NONBLOCK

[Martin Wilck <mwilck@suse.com>]

On Tue, 2020-08-11 at 07:26 -0400, Michael S. Tsirkin wrote:
> On Wed, Jul 15, 2020 at 03:32:55PM +0200, mwilck@suse.com wrote:
> >  drivers/char/hw_random/virtio-rng.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/char/hw_random/virtio-rng.c
> > b/drivers/char/hw_random/virtio-rng.c
> > index 79a6e47b5fbc..984713b35892 100644
> > --- a/drivers/char/hw_random/virtio-rng.c
> > +++ b/drivers/char/hw_random/virtio-rng.c
> > @@ -59,6 +59,20 @@ static int virtio_read(struct hwrng *rng, void
> > *buf, size_t size, bool wait)
> >  	if (vi->hwrng_removed)
> >  		return -ENODEV;
> >  
> > +	/*
> > +	 * If the previous call was non-blocking, we may have got some
> > +	 * randomness already.
> > +	 */
> > +	if (vi->busy && completion_done(&vi->have_data)) {
> > +		unsigned int len;
> > +
> > +		vi->busy = false;
> > +		len = vi->data_avail > size ? size : vi->data_avail;
> > +		vi->data_avail -= len;
> 
> I wonder what purpose does this line serve: busy is false
> which basically means data_avail is invalid, right?
> A following non blocking call will not enter here.

Well, I thought this is just how reading data normally works. But
you're right, the remainder will not be used. I can remove the line, or
reset data_avail to 0 at this point. What do you prefer?

Regards,
Martin