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/* SPDX-License-Identifier: MIT
*
* ring.h
*
* Shared producer-consumer ring macros.
*
* Tim Deegan and Andrew Warfield November 2004.
*/
#ifndef __XEN_PUBLIC_IO_RING_H__
#define __XEN_PUBLIC_IO_RING_H__
/*
* When #include'ing this header, you need to provide the following
* declaration upfront:
* - standard integers types (u8, u16, etc)
* They are provided by stdint.h of the standard headers.
*
* In addition, if you intend to use the FLEX macros, you also need to
* provide the following, before invoking the FLEX macros:
* - size_t
* - memcpy
* - grant_ref_t
* These declarations are provided by string.h of the standard headers,
* and grant_table.h from the Xen public headers.
*/
#include <xen/interface/grant_table.h>
typedef unsigned int RING_IDX;
/* Round a 32-bit unsigned constant down to the nearest power of two. */
#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x) >> 2) << 2 : __RD2(_x))
#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x) >> 4) << 4 : __RD4(_x))
#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x) >> 8) << 8 : __RD8(_x))
#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x) >> 16) << 16 : __RD16(_x))
/*
* Calculate size of a shared ring, given the total available space for the
* ring and indexes (_sz), and the name tag of the request/response structure.
* A ring contains as many entries as will fit, rounded down to the nearest
* power of two (so we can mask with (size-1) to loop around).
*/
#define __CONST_RING_SIZE(_s, _sz) \
(__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
sizeof(((struct _s##_sring *)0)->ring[0])))
/*
* The same for passing in an actual pointer instead of a name tag.
*/
#define __RING_SIZE(_s, _sz) \
(__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
/*
* Macros to make the correct C datatypes for a new kind of ring.
*
* To make a new ring datatype, you need to have two message structures,
* let's say request_t, and response_t already defined.
*
* In a header where you want the ring datatype declared, you then do:
*
* DEFINE_RING_TYPES(mytag, request_t, response_t);
*
* These expand out to give you a set of types, as you can see below.
* The most important of these are:
*
* mytag_sring_t - The shared ring.
* mytag_front_ring_t - The 'front' half of the ring.
* mytag_back_ring_t - The 'back' half of the ring.
*
* To initialize a ring in your code you need to know the location and size
* of the shared memory area (PAGE_SIZE, for instance). To initialise
* the front half:
*
* mytag_front_ring_t front_ring;
* SHARED_RING_INIT((mytag_sring_t *)shared_page);
* FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
*
* Initializing the back follows similarly (note that only the front
* initializes the shared ring):
*
* mytag_back_ring_t back_ring;
* BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
*/
#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
\
/* Shared ring entry */ \
union __name##_sring_entry { \
__req_t req; \
__rsp_t rsp; \
}; \
\
/* Shared ring page */ \
struct __name##_sring { \
RING_IDX req_prod, req_event; \
RING_IDX rsp_prod, rsp_event; \
union { \
struct { \
u8 smartpoll_active; \
} netif; \
struct { \
u8 msg; \
} tapif_user; \
u8 pvt_pad[4]; \
} pvt; \
u8 __pad[44]; \
union __name##_sring_entry ring[1]; /* variable-length */ \
}; \
\
/* "Front" end's private variables */ \
struct __name##_front_ring { \
RING_IDX req_prod_pvt; \
RING_IDX rsp_cons; \
unsigned int nr_ents; \
struct __name##_sring *sring; \
}; \
\
/* "Back" end's private variables */ \
struct __name##_back_ring { \
RING_IDX rsp_prod_pvt; \
RING_IDX req_cons; \
unsigned int nr_ents; \
struct __name##_sring *sring; \
}; \
\
/* Syntactic sugar */ \
typedef struct __name##_sring __name##_sring_t; \
typedef struct __name##_front_ring __name##_front_ring_t; \
typedef struct __name##_back_ring __name##_back_ring_t
/*
* Macros for manipulating rings.
*
* FRONT_RING_whatever works on the "front end" of a ring: here
* requests are pushed on to the ring and responses taken off it.
*
* BACK_RING_whatever works on the "back end" of a ring: here
* requests are taken off the ring and responses put on.
*
* N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
* This is OK in 1-for-1 request-response situations where the
* requestor (front end) never has more than RING_SIZE()-1
* outstanding requests.
*/
/* Initialising empty rings */
#define SHARED_RING_INIT(_s) do { \
(_s)->req_prod = (_s)->rsp_prod = 0; \
(_s)->req_event = (_s)->rsp_event = 1; \
(void)memset((_s)->pvt.pvt_pad, 0, sizeof((_s)->pvt.pvt_pad)); \
(void)memset((_s)->__pad, 0, sizeof((_s)->__pad)); \
} while (0)
#define FRONT_RING_INIT(_r, _s, __size) do { \
(_r)->req_prod_pvt = 0; \
(_r)->rsp_cons = 0; \
(_r)->nr_ents = __RING_SIZE(_s, __size); \
(_r)->sring = (_s); \
} while (0)
#define BACK_RING_INIT(_r, _s, __size) do { \
(_r)->rsp_prod_pvt = 0; \
(_r)->req_cons = 0; \
(_r)->nr_ents = __RING_SIZE(_s, __size); \
(_r)->sring = (_s); \
} while (0)
/* How big is this ring? */
#define RING_SIZE(_r) \
((_r)->nr_ents)
/* Number of free requests (for use on front side only). */
#define RING_FREE_REQUESTS(_r) \
(RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
/* Test if there is an empty slot available on the front ring.
* (This is only meaningful from the front. )
*/
#define RING_FULL(_r) \
(RING_FREE_REQUESTS(_r) == 0)
/* Test if there are outstanding messages to be processed on a ring. */
#define RING_HAS_UNCONSUMED_RESPONSES(_r) \
((_r)->sring->rsp_prod - (_r)->rsp_cons)
#ifdef __GNUC__
#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; \
})
#else
/* Same as above, but without the nice GCC ({ ... }) syntax. */
#define RING_HAS_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
/* Direct access to individual ring elements, by index. */
#define RING_GET_REQUEST(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
/*
* Get a local copy of a request.
*
* Use this in preference to RING_GET_REQUEST() so all processing is
* done on a local copy that cannot be modified by the other end.
*
* Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this
* to be ineffective where _req is a struct which consists of only bitfields.
*/
#define RING_COPY_REQUEST(_r, _idx, _req) do { \
/* Use volatile to force the copy into _req. */ \
*(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \
} while (0)
#define RING_GET_RESPONSE(_r, _idx) \
(&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
/* Loop termination condition: Would the specified index overflow the ring? */
#define RING_REQUEST_CONS_OVERFLOW(_r, _cons) \
(((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
/* Ill-behaved frontend determination: Can there be this many requests? */
#define RING_REQUEST_PROD_OVERFLOW(_r, _prod) \
(((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
#define RING_PUSH_REQUESTS(_r) do { \
xen_wmb(); /* back sees requests /before/ updated producer index */ \
(_r)->sring->req_prod = (_r)->req_prod_pvt; \
} while (0)
#define RING_PUSH_RESPONSES(_r) do { \
xen_wmb(); /* front sees resps /before/ updated producer index */ \
(_r)->sring->rsp_prod = (_r)->rsp_prod_pvt; \
} while (0)
/*
* Notification hold-off (req_event and rsp_event):
*
* When queueing requests or responses on a shared ring, it may not always be
* necessary to notify the remote end. For example, if requests are in flight
* in a backend, the front may be able to queue further requests without
* notifying the back (if the back checks for new requests when it queues
* responses).
*
* When enqueuing requests or responses:
*
* Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
* is a boolean return value. True indicates that the receiver requires an
* asynchronous notification.
*
* After dequeuing requests or responses (before sleeping the connection):
*
* Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
* The second argument is a boolean return value. True indicates that there
* are pending messages on the ring (i.e., the connection should not be put
* to sleep).
*
* These macros will set the req_event/rsp_event field to trigger a
* notification on the very next message that is enqueued. If you want to
* create batches of work (i.e., only receive a notification after several
* messages have been enqueued) then you will need to create a customised
* version of the FINAL_CHECK macro in your own code, which sets the event
* field appropriately.
*/
#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
RING_IDX __old = (_r)->sring->req_prod; \
RING_IDX __new = (_r)->req_prod_pvt; \
xen_wmb(); /* back sees requests /before/ updated producer index */ \
(_r)->sring->req_prod = __new; \
xen_mb(); /* back sees new requests /before/ we check req_event */ \
(_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
(RING_IDX)(__new - __old)); \
} while (0)
#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
RING_IDX __old = (_r)->sring->rsp_prod; \
RING_IDX __new = (_r)->rsp_prod_pvt; \
xen_wmb(); /* front sees resps /before/ updated producer index */ \
(_r)->sring->rsp_prod = __new; \
xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
(_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
(RING_IDX)(__new - __old)); \
} while (0)
#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
if (_work_to_do) \
break; \
(_r)->sring->req_event = (_r)->req_cons + 1; \
xen_mb(); \
(_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r); \
} while (0)
#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
if (_work_to_do) \
break; \
(_r)->sring->rsp_event = (_r)->rsp_cons + 1; \
xen_mb(); \
(_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
} while (0)
/*
* DEFINE_XEN_FLEX_RING_AND_INTF defines two monodirectional rings and
* functions to check if there is data on the ring, and to read and
* write to them.
*
* DEFINE_XEN_FLEX_RING is similar to DEFINE_XEN_FLEX_RING_AND_INTF, but
* does not define the indexes page. As different protocols can have
* extensions to the basic format, this macro allow them to define their
* own struct.
*
* XEN_FLEX_RING_SIZE
* Convenience macro to calculate the size of one of the two rings
* from the overall order.
*
* $NAME_mask
* Function to apply the size mask to an index, to reduce the index
* within the range [0-size].
*
* $NAME_read_packet
* Function to read data from the ring. The amount of data to read is
* specified by the "size" argument.
*
* $NAME_write_packet
* Function to write data to the ring. The amount of data to write is
* specified by the "size" argument.
*
* $NAME_get_ring_ptr
* Convenience function that returns a pointer to read/write to the
* ring at the right location.
*
* $NAME_data_intf
* Indexes page, shared between frontend and backend. It also
* contains the array of grant refs.
*
* $NAME_queued
* Function to calculate how many bytes are currently on the ring,
* ready to be read. It can also be used to calculate how much free
* space is currently on the ring (XEN_FLEX_RING_SIZE() -
* $NAME_queued()).
*/
#ifndef XEN_PAGE_SHIFT
/* The PAGE_SIZE for ring protocols and hypercall interfaces is always
* 4K, regardless of the architecture, and page granularity chosen by
* operating systems.
*/
#define XEN_PAGE_SHIFT 12
#endif
#define XEN_FLEX_RING_SIZE(order) \
(1UL << ((order) + XEN_PAGE_SHIFT - 1))
#define DEFINE_XEN_FLEX_RING(name) \
static inline RING_IDX name##_mask(RING_IDX idx, RING_IDX ring_size) \
{ \
return idx & (ring_size - 1); \
} \
\
static inline unsigned char *name##_get_ring_ptr(unsigned char *buf, \
RING_IDX idx, \
RING_IDX ring_size) \
{ \
return buf + name##_mask(idx, ring_size); \
} \
\
static inline void name##_read_packet(void *opaque, \
const unsigned char *buf, \
size_t size, \
RING_IDX masked_prod, \
RING_IDX *masked_cons, \
RING_IDX ring_size) \
{ \
if (*masked_cons < masked_prod || \
size <= ring_size - *masked_cons) { \
memcpy(opaque, buf + *masked_cons, size); \
} else { \
memcpy(opaque, buf + *masked_cons, ring_size - *masked_cons); \
memcpy((unsigned char *)opaque + ring_size - *masked_cons, buf, \
size - (ring_size - *masked_cons)); \
} \
*masked_cons = name##_mask(*masked_cons + size, ring_size); \
} \
\
static inline void name##_write_packet(unsigned char *buf, \
const void *opaque, \
size_t size, \
RING_IDX *masked_prod, \
RING_IDX masked_cons, \
RING_IDX ring_size) \
{ \
if (*masked_prod < masked_cons || \
size <= ring_size - *masked_prod) { \
memcpy(buf + *masked_prod, opaque, size); \
} else { \
memcpy(buf + *masked_prod, opaque, ring_size - *masked_prod); \
memcpy(buf, (unsigned char *)opaque + (ring_size - *masked_prod), \
size - (ring_size - *masked_prod)); \
} \
*masked_prod = name##_mask(*masked_prod + size, ring_size); \
} \
\
static inline RING_IDX name##_queued(RING_IDX prod, \
RING_IDX cons, \
RING_IDX ring_size) \
{ \
RING_IDX size; \
\
if (prod == cons) \
return 0; \
\
prod = name##_mask(prod, ring_size); \
cons = name##_mask(cons, ring_size); \
\
if (prod == cons) \
return ring_size; \
\
if (prod > cons) \
size = prod - cons; \
else \
size = ring_size - (cons - prod); \
return size; \
} \
\
struct name##_data { \
unsigned char *in; /* half of the allocation */ \
unsigned char *out; /* half of the allocation */ \
}
#define DEFINE_XEN_FLEX_RING_AND_INTF(name) \
struct name##_data_intf { \
RING_IDX in_cons, in_prod; \
\
u8 pad1[56]; \
\
RING_IDX out_cons, out_prod; \
\
u8 pad2[56]; \
\
RING_IDX ring_order; \
grant_ref_t ref[]; \
}; \
DEFINE_XEN_FLEX_RING(name)
#endif /* __XEN_PUBLIC_IO_RING_H__ */
/*
* Local variables:
* mode: C
* c-file-style: "BSD"
* c-basic-offset: 4
* tab-width: 8
* indent-tabs-mode: nil
* End:
*/
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