Re: [Xen-devel] [Problem] about src/xen/include/public/io/ring.h

[éç <aware.why@xxxxxxxxx>]

On Thu, Apr 11, 2013 at 9:20 PM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:

On Thu, Apr 11, 2013 at 03:46:25PM +0800, éç wrote:
> ÂI means, in ring.h,
> The macro for unconsumed response is :
> Â207#define RING_HAS_UNCONSUMED_RESPONSES(_r)
> \
> Â208 Â Â((_r)->sring->rsp_prod - (_r)->rsp_cons)
>

> *Should the macro for unconsumed request be written like this:*

> Â#define RING_HAS_UNCONSUMED_REQUESTS(_r) Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â \
> Â Â Â((_r)->sring->req_prod - (_r)->req_cons)
>

Please don't top post.

It is close to that in the code:

#define RING_HAS_UNCONSUMED_REQUESTS(_r) Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â\
  ({                                 Â\

    unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;   Â\

    unsigned int rsp = RING_SIZE(_r) -               Â\

             Â((_r)->req_cons - (_r)->rsp_prod_pvt);    \

    req < rsp ? req : rsp;                     Â\

  })

Can you figure out why it has the check against resp_cons and rsp_prod_pvt ?

Assume X = (_r)->req_cons - (_r)->rsp_prod_pvt and Y = number of free ring buffers for responder(backend driver), they are equal in amount, is that?

Then rsp = RING_SIZE(r) - (X - Y), ÂI can't figure out this and the return value `Âreq < rsp ? req : rsp` ?

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