[PATCH v2] public: add RING_NR_UNCONSUMED_*() macros to ring.h

[Juergen Gross <jgross@xxxxxxxx>]

Today RING_HAS_UNCONSUMED_*() macros are returning the number of
unconsumed requests or responses instead of a boolean as the name of
the macros would imply.

As this "feature" is already being used, rename the macros to
RING_NR_UNCONSUMED_*() and define the RING_HAS_UNCONSUMED_*() macros
by using the new RING_NR_UNCONSUMED_*() macros. In order to avoid
future misuse let RING_HAS_UNCONSUMED_*() optionally really return a
boolean (can be activated by defining RING_HAS_UNCONSUMED_IS_BOOL).

Note that the known misuses need to be switched to the new
RING_NR_UNCONSUMED_*() macros when using this version of ring.h.

Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>
Cc: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
Cc: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
Cc: Paul Durrant <paul@xxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
I have checked Xen, Mini-OS, qemu, grub2, OVMF and Linux kernel for
misuses of the RING_HAS_UNCONSUMED_*() macros. There is currently only
one instance in the Linux kernel netback driver. The BSDs, UNIKRAFT
and Windows PV drivers should be checked for misuse, too.
V2: make RING_HAS_UNCONSUMED_*() returning a bool optional (Jan Beulich)
---
 xen/include/public/io/ring.h | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
index c486c457e0..a7f492db39 100644
--- a/xen/include/public/io/ring.h
+++ b/xen/include/public/io/ring.h
@@ -208,11 +208,11 @@ typedef struct __name##_back_ring __name##_back_ring_t
     (RING_FREE_REQUESTS(_r) == 0)
 
 /* Test if there are outstanding messages to be processed on a ring. */
-#define RING_HAS_UNCONSUMED_RESPONSES(_r)                               \
+#define RING_NR_UNCONSUMED_RESPONSES(_r)                                \
     ((_r)->sring->rsp_prod - (_r)->rsp_cons)
 
 #ifdef __GNUC__
-#define RING_HAS_UNCONSUMED_REQUESTS(_r) ({                             \
+#define RING_NR_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);                          \
@@ -220,13 +220,25 @@ typedef struct __name##_back_ring __name##_back_ring_t
 })
 #else
 /* Same as above, but without the nice GCC ({ ... }) syntax. */
-#define RING_HAS_UNCONSUMED_REQUESTS(_r)                                \
+#define RING_NR_UNCONSUMED_REQUESTS(_r)                                 \
     ((((_r)->sring->req_prod - (_r)->req_cons) <                        \
       (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ?        \
      ((_r)->sring->req_prod - (_r)->req_cons) :                         \
      (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
 #endif
 
+#ifdef RING_HAS_UNCONSUMED_IS_BOOL
+/*
+ * These variants should only be used in case no caller is abusing them for
+ * obtaining the number of unconsumed responses/requests.
+ */
+#define RING_HAS_UNCONSUMED_RESPONSES(_r) (!!RING_NR_UNCONSUMED_RESPONSES(_r))
+#define RING_HAS_UNCONSUMED_REQUESTS(_r)  (!!RING_NR_UNCONSUMED_REQUESTS(_r))
+#else
+#define RING_HAS_UNCONSUMED_RESPONSES(_r) RING_NR_UNCONSUMED_RESPONSES(_r)
+#define RING_HAS_UNCONSUMED_REQUESTS(_r)  RING_NR_UNCONSUMED_REQUESTS(_r)
+#endif
+
 /* Direct access to individual ring elements, by index. */
 #define RING_GET_REQUEST(_r, _idx)                                      \
     (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
-- 
2.26.2