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

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Date:	Mon, 21 Mar 2016 23:42:48 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs



> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Monday, March 21, 2016 1:29 AM
> To: KY Srinivasan <kys@...rosoft.com>
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com
> Subject: Re: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs
> 
> "K. Y. Srinivasan" <kys@...rosoft.com> writes:
> 
> > Implement copy-free read APIs.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > ---
> >  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