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ring.h
/* 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 (uint8_t, uint16_t, 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 ring; * XEN_FRONT_RING_INIT(&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; \ uint8_t __pad[48]; \ union __name##_sring_entry ring[]; \ }; \ \ /* "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; \ }; \ \ /* * 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)->__pad, 0, sizeof((_s)->__pad)); \ } while(0) #define FRONT_RING_ATTACH(_r, _s, _i, __size) do { \ (_r)->req_prod_pvt = (_i); \ (_r)->rsp_cons = (_i); \ (_r)->nr_ents = __RING_SIZE(_s, __size); \ (_r)->sring = (_s); \ } while (0) #define FRONT_RING_INIT(_r, _s, __size) FRONT_RING_ATTACH(_r, _s, 0, __size) #define XEN_FRONT_RING_INIT(r, s, size) do { \ SHARED_RING_INIT(s); \ FRONT_RING_INIT(r, s, size); \ } while (0) #define BACK_RING_ATTACH(_r, _s, _i, __size) do { \ (_r)->rsp_prod_pvt = (_i); \ (_r)->req_cons = (_i); \ (_r)->nr_ents = __RING_SIZE(_s, __size); \ (_r)->sring = (_s); \ } while (0) #define BACK_RING_INIT(_r, _s, __size) BACK_RING_ATTACH(_r, _s, 0, __size) /* 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 XEN_RING_NR_UNCONSUMED_RESPONSES(_r) \ ((_r)->sring->rsp_prod - (_r)->rsp_cons) #define XEN_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); \ req < rsp ? req : rsp; \ }) #define RING_HAS_UNCONSUMED_RESPONSES(_r) \ (!!XEN_RING_NR_UNCONSUMED_RESPONSES(_r)) #define RING_HAS_UNCONSUMED_REQUESTS(_r) \ (!!XEN_RING_NR_UNCONSUMED_REQUESTS(_r)) /* 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)) /* * Get a local copy of a request/response. * * Use this in preference to RING_GET_{REQUEST,RESPONSE}() 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 dest is a struct which consists of only bitfields. */ #define RING_COPY_(type, r, idx, dest) do { \ /* Use volatile to force the copy into dest. */ \ *(dest) = *(volatile typeof(dest))RING_GET_##type(r, idx); \ } while (0) #define RING_COPY_REQUEST(r, idx, req) RING_COPY_(REQUEST, r, idx, req) #define RING_COPY_RESPONSE(r, idx, rsp) RING_COPY_(RESPONSE, r, idx, 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)) /* Ill-behaved backend determination: Can there be this many responses? */ #define RING_RESPONSE_PROD_OVERFLOW(_r, _prod) \ (((_prod) - (_r)->rsp_cons) > RING_SIZE(_r)) #define RING_PUSH_REQUESTS(_r) do { \ virt_wmb(); /* back sees requests /before/ updated producer index */\ (_r)->sring->req_prod = (_r)->req_prod_pvt; \ } while (0) #define RING_PUSH_RESPONSES(_r) do { \ virt_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; \ virt_wmb(); /* back sees requests /before/ updated producer index */\ (_r)->sring->req_prod = __new; \ virt_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; \ virt_wmb(); /* front sees resps /before/ updated producer index */ \ (_r)->sring->rsp_prod = __new; \ virt_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; \ virt_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; \ virt_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; \ \ uint8_t pad1[56]; \ \ RING_IDX out_cons, out_prod; \ \ uint8_t pad2[56]; \ \ RING_IDX ring_order; \ grant_ref_t ref[]; \ }; \ DEFINE_XEN_FLEX_RING(name) #endif /* __XEN_PUBLIC_IO_RING_H__ */
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