RE: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs

From: KY Srinivasan
Date: Mon Mar 21 2016 - 19:43:10 EST




> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
> Sent: Monday, March 21, 2016 1:29 AM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
> jasowang@xxxxxxxxxx
> Subject: Re: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs
>
> "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> writes:
>
> > Implement copy-free read APIs.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> > ---
> > drivers/hv/ring_buffer.c | 55
> ++++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/hyperv.h | 6 +++++
> > 2 files changed, 61 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> > index c2c2b2e..c80e1f3 100644
> > --- a/drivers/hv/ring_buffer.c
> > +++ b/drivers/hv/ring_buffer.c
> > @@ -444,3 +444,58 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info
> *inring_info,
> >
> > return ret;
> > }
> > +
> > +/*
> > + * In-place read functions.
> > + */
> > +bool get_next_pkt_raw(struct vmbus_channel *channel,
> > + struct vmpacket_descriptor **desc)
>
> I suggest we make these functions return pointers and use
> ERR_PTR()/IS_ERR() when we need to return an error.

Either we get a pointer to a descriptor or not; there is no other
error here. I will change the signature accordingly.

>
> > +{
> > + struct hv_ring_buffer_info *ring_info = &channel->inbound;
> > + u32 read_loc = ring_info->ring_buffer->read_index;
> > + void *ring_buffer = hv_get_ring_buffer(ring_info);
> > + struct vmpacket_descriptor *cur_desc;
> > + u32 packetlen;
> > + u32 dsize = ring_info->ring_datasize;
> > + u32 bytes_avail_toread = hv_get_bytes_to_read(ring_info);
> > +
> > + if (bytes_avail_toread < sizeof(struct vmpacket_descriptor))
> > + return false;
> > +
> > + if ((read_loc + sizeof(*desc)) > dsize)
> > + return false;
> > +
> > + cur_desc = ring_buffer + read_loc;
> > + packetlen = cur_desc->len8 << 3;
> > +
> > + if ((read_loc + packetlen + 8) > (dsize - 1))
>
> Could you please add a define for this '8'?

Sure.

K. Y