From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zoltan Kiss <zoltan.kiss@citrix.com>
Subject: RING_HAS_UNCONSUMED_REQUESTS oddness
Date: Thu, 6 Mar 2014 15:47:08 +0000
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To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>
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Hi,

I was wondering for a while why this macro looks like this:

#define RING_HAS_UNCONSUMED_REQUESTS(_r)				\
    ({									\
	unsigned int req = (_r)->sring->req_prod - (_r)->req_cons;	\
	unsigned int rsp = RING_SIZE(_r) -				\
			   ((_r)->req_cons - (_r)->rsp_prod_pvt);	\
	req < rsp ? req : rsp;						\
    })

I would expect to check prod - cons, like RING_HAS_UNCONSUMED_RESPONSES does:

#define RING_HAS_UNCONSUMED_RESPONSES(_r)				\
    ((_r)->sring->rsp_prod - (_r)->rsp_cons)

By my understanding, there is no way rsp could be smaller than req, so
there is no point having this. Am I missing something?

Regards,

Zoli