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

[éç <aware.why@xxxxxxxxx>]

On Mon, Apr 8, 2013 at 9:32 PM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:

On Mon, Apr 08, 2013 at 04:10:49PM +0800, éç wrote:
> Hi,
> Â Â there is a macro in io/ring.h as follows:
>
> 211#define RING_HAS_UNCONSUMED_REQUESTS(_r) ({
> \ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â |
> 212 Â Âunsigned int req = (_r)->sring->req_prod - (_r)->req_cons;
> Â\
> 213 Â Âunsigned int rsp = RING_SIZE(_r) -
> Â\
> 214 Â Â Â Â((_r)->req_cons - (_r)->rsp_prod_pvt);
> Â\
> 215 Â Âreq < rsp ? req : rsp;
> Â\
> 216})
>
> Anyone could explain this?

Which part are you unclear about?

I might be easier if you deconstruct the macro and write out
inthe code. That should give you an idea of what it does.
<hint: Figure out first what RING_SIZE comes out to>

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Â

Why does the macro for response is :Â

207#define RING_HAS_UNCONSUMED_RESPONSES(_r) Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â \

208 Â Â((_r)->sring->rsp_prod - (_r)->rsp_cons)

why not the macro for request written like this:

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

  ((_r)->sring->req_prod - (_r)->req_cons)

The RING_SIZE means the maximum number for the shared ring to accommodate the req/resp message struct, is that?

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