ref: b7ee84c65da44dfed3d8ceca424da511b0c1412f
dir: /sys/src/9/xen/xen-public/io/ring.h/
/****************************************************************************** * ring.h * * Shared producer-consumer ring macros. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to * deal in the Software without restriction, including without limitation the * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or * sell copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER * DEALINGS IN THE SOFTWARE. * * 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 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 { \ uint8_t smartpoll_active; \ } netif; \ struct { \ uint8_t msg; \ } tapif_user; \ uint8_t pvt_pad[4]; \ } private; \ uint8_t __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)->private.pvt_pad, 0, sizeof((_s)->private.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)) #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: */