/****************************************************************************** | |
* ring.h | |
* | |
* Shared producer-consumer ring macros. | |
* | |
* SPDX-License-Identifier: MIT | |
* | |
* Tim Deegan and Andrew Warfield November 2004. | |
*/ | |
#ifndef __XEN_PUBLIC_IO_RING_H__ | |
#define __XEN_PUBLIC_IO_RING_H__ | |
#include "../xen-compat.h" | |
#if __XEN_INTERFACE_VERSION__ < 0x00030208 | |
#define xen_mb() mb() | |
#define xen_rmb() rmb() | |
#define xen_wmb() wmb() | |
#endif | |
typedef UINT32 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) - (INTN)(_s)->ring + (INTN)(_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 { \ | |
UINT8 smartpoll_active; \ | |
} netif; \ | |
struct { \ | |
UINT8 msg; \ | |
} tapif_user; \ | |
UINT8 pvt_pad[4]; \ | |
} private; \ | |
UINT8 __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; \ | |
UINT32 nr_ents; \ | |
struct __name##_sring *sring; \ | |
}; \ | |
\ | |
/* "Back" end's private variables */ \ | |
struct __name##_back_ring { \ | |
RING_IDX rsp_prod_pvt; \ | |
RING_IDX req_cons; \ | |
UINT32 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)ZeroMem((_s)->private.pvt_pad, sizeof((_s)->private.pvt_pad)); \ | |
(VOID)ZeroMem((_s)->__pad, 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) ({ \ | |
UINT32 req = (_r)->sring->req_prod - (_r)->req_cons; \ | |
UINT32 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)) | |
#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) | |
#endif /* __XEN_PUBLIC_IO_RING_H__ */ | |
/* | |
* Local variables: | |
* mode: C | |
* c-file-style: "BSD" | |
* c-basic-offset: 4 | |
* tab-width: 4 | |
* indent-tabs-mode: nil | |
* End: | |
*/ |