843e19887f64dde75055cf8842fc4db2171eff45johnlev/******************************************************************************
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Shared producer-consumer ring macros.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Permission is hereby granted, free of charge, to any person obtaining a copy
843e19887f64dde75055cf8842fc4db2171eff45johnlev * of this software and associated documentation files (the "Software"), to
843e19887f64dde75055cf8842fc4db2171eff45johnlev * deal in the Software without restriction, including without limitation the
843e19887f64dde75055cf8842fc4db2171eff45johnlev * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
843e19887f64dde75055cf8842fc4db2171eff45johnlev * sell copies of the Software, and to permit persons to whom the Software is
843e19887f64dde75055cf8842fc4db2171eff45johnlev * furnished to do so, subject to the following conditions:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * The above copyright notice and this permission notice shall be included in
843e19887f64dde75055cf8842fc4db2171eff45johnlev * all copies or substantial portions of the Software.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
843e19887f64dde75055cf8842fc4db2171eff45johnlev * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
843e19887f64dde75055cf8842fc4db2171eff45johnlev * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
843e19887f64dde75055cf8842fc4db2171eff45johnlev * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
843e19887f64dde75055cf8842fc4db2171eff45johnlev * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
843e19887f64dde75055cf8842fc4db2171eff45johnlev * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
843e19887f64dde75055cf8842fc4db2171eff45johnlev * DEALINGS IN THE SOFTWARE.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Tim Deegan and Andrew Warfield November 2004.
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Round a 32-bit unsigned constant down to the nearest power of two. */
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define __RD2(_x) (((_x) & 0x00000002) ? 0x2 : ((_x) & 0x1))
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define __RD4(_x) (((_x) & 0x0000000c) ? __RD2((_x)>>2)<<2 : __RD2(_x))
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define __RD8(_x) (((_x) & 0x000000f0) ? __RD4((_x)>>4)<<4 : __RD4(_x))
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define __RD16(_x) (((_x) & 0x0000ff00) ? __RD8((_x)>>8)<<8 : __RD8(_x))
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define __RD32(_x) (((_x) & 0xffff0000) ? __RD16((_x)>>16)<<16 : __RD16(_x))
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Calculate size of a shared ring, given the total available space for the
843e19887f64dde75055cf8842fc4db2171eff45johnlev * ring and indexes (_sz), and the name tag of the request/response structure.
876de206688d9fe008ad80c116a23a56701579d1Richard Lowe * A ring contains as many entries as will fit, rounded down to the nearest
843e19887f64dde75055cf8842fc4db2171eff45johnlev * power of two (so we can mask with (size-1) to loop around).
876de206688d9fe008ad80c116a23a56701579d1Richard Lowe (__RD32(((_sz) - offsetof(struct _s##_sring, ring)) / \
876de206688d9fe008ad80c116a23a56701579d1Richard Lowe * The same for passing in an actual pointer instead of a name tag.
843e19887f64dde75055cf8842fc4db2171eff45johnlev (__RD32(((_sz) - (long)(_s)->ring + (long)(_s)) / sizeof((_s)->ring[0])))
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Macros to make the correct C datatypes for a new kind of ring.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * To make a new ring datatype, you need to have two message structures,
843e19887f64dde75055cf8842fc4db2171eff45johnlev * let's say request_t, and response_t already defined.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * In a header where you want the ring datatype declared, you then do:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * DEFINE_RING_TYPES(mytag, request_t, response_t);
843e19887f64dde75055cf8842fc4db2171eff45johnlev * These expand out to give you a set of types, as you can see below.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * The most important of these are:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * mytag_sring_t - The shared ring.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * mytag_front_ring_t - The 'front' half of the ring.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * mytag_back_ring_t - The 'back' half of the ring.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * To initialize a ring in your code you need to know the location and size
843e19887f64dde75055cf8842fc4db2171eff45johnlev * of the shared memory area (PAGE_SIZE, for instance). To initialise
843e19887f64dde75055cf8842fc4db2171eff45johnlev * the front half:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * mytag_front_ring_t front_ring;
843e19887f64dde75055cf8842fc4db2171eff45johnlev * SHARED_RING_INIT((mytag_sring_t *)shared_page);
843e19887f64dde75055cf8842fc4db2171eff45johnlev * FRONT_RING_INIT(&front_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Initializing the back follows similarly (note that only the front
843e19887f64dde75055cf8842fc4db2171eff45johnlev * initializes the shared ring):
843e19887f64dde75055cf8842fc4db2171eff45johnlev * mytag_back_ring_t back_ring;
843e19887f64dde75055cf8842fc4db2171eff45johnlev * BACK_RING_INIT(&back_ring, (mytag_sring_t *)shared_page, PAGE_SIZE);
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define DEFINE_RING_TYPES(__name, __req_t, __rsp_t) \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Shared ring entry */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Shared ring page */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev union __name##_sring_entry ring[1]; /* variable-length */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* "Front" end's private variables */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev unsigned int nr_ents; \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* "Back" end's private variables */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev unsigned int nr_ents; \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Syntactic sugar */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlevtypedef struct __name##_front_ring __name##_front_ring_t; \
843e19887f64dde75055cf8842fc4db2171eff45johnlevtypedef struct __name##_back_ring __name##_back_ring_t
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Macros for manipulating rings.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * FRONT_RING_whatever works on the "front end" of a ring: here
843e19887f64dde75055cf8842fc4db2171eff45johnlev * requests are pushed on to the ring and responses taken off it.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * BACK_RING_whatever works on the "back end" of a ring: here
843e19887f64dde75055cf8842fc4db2171eff45johnlev * requests are taken off the ring and responses put on.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * N.B. these macros do NO INTERLOCKS OR FLOW CONTROL.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * This is OK in 1-for-1 request-response situations where the
843e19887f64dde75055cf8842fc4db2171eff45johnlev * requestor (front end) never has more than RING_SIZE()-1
843e19887f64dde75055cf8842fc4db2171eff45johnlev * outstanding requests.
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Initialising empty rings */
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Initialize to existing shared indexes -- for recovery */
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* How big is this ring? */
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Number of free requests (for use on front side only). */
843e19887f64dde75055cf8842fc4db2171eff45johnlev (RING_SIZE(_r) - ((_r)->req_prod_pvt - (_r)->rsp_cons))
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Test if there is an empty slot available on the front ring.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * (This is only meaningful from the front. )
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Test if there are outstanding messages to be processed on a ring. */
843e19887f64dde75055cf8842fc4db2171eff45johnlev unsigned int req = (_r)->sring->req_prod - (_r)->req_cons; \
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Same as above, but without the nice GCC ({ ... }) syntax. */
843e19887f64dde75055cf8842fc4db2171eff45johnlev (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt))) ? \
843e19887f64dde75055cf8842fc4db2171eff45johnlev (RING_SIZE(_r) - ((_r)->req_cons - (_r)->rsp_prod_pvt)))
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Direct access to individual ring elements, by index. */
843e19887f64dde75055cf8842fc4db2171eff45johnlev (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req))
843e19887f64dde75055cf8842fc4db2171eff45johnlev (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp))
843e19887f64dde75055cf8842fc4db2171eff45johnlev/* Loop termination condition: Would the specified index overflow the ring? */
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_wmb(); /* back sees requests /before/ updated producer index */ \
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_wmb(); /* front sees resps /before/ updated producer index */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Notification hold-off (req_event and rsp_event):
843e19887f64dde75055cf8842fc4db2171eff45johnlev * When queueing requests or responses on a shared ring, it may not always be
843e19887f64dde75055cf8842fc4db2171eff45johnlev * necessary to notify the remote end. For example, if requests are in flight
843e19887f64dde75055cf8842fc4db2171eff45johnlev * in a backend, the front may be able to queue further requests without
843e19887f64dde75055cf8842fc4db2171eff45johnlev * notifying the back (if the back checks for new requests when it queues
843e19887f64dde75055cf8842fc4db2171eff45johnlev * responses).
843e19887f64dde75055cf8842fc4db2171eff45johnlev * When enqueuing requests or responses:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Use RING_PUSH_{REQUESTS,RESPONSES}_AND_CHECK_NOTIFY(). The second argument
843e19887f64dde75055cf8842fc4db2171eff45johnlev * is a boolean return value. True indicates that the receiver requires an
843e19887f64dde75055cf8842fc4db2171eff45johnlev * asynchronous notification.
843e19887f64dde75055cf8842fc4db2171eff45johnlev * After dequeuing requests or responses (before sleeping the connection):
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Use RING_FINAL_CHECK_FOR_REQUESTS() or RING_FINAL_CHECK_FOR_RESPONSES().
843e19887f64dde75055cf8842fc4db2171eff45johnlev * The second argument is a boolean return value. True indicates that there
843e19887f64dde75055cf8842fc4db2171eff45johnlev * are pending messages on the ring (i.e., the connection should not be put
843e19887f64dde75055cf8842fc4db2171eff45johnlev * to sleep).
843e19887f64dde75055cf8842fc4db2171eff45johnlev * These macros will set the req_event/rsp_event field to trigger a
843e19887f64dde75055cf8842fc4db2171eff45johnlev * notification on the very next message that is enqueued. If you want to
843e19887f64dde75055cf8842fc4db2171eff45johnlev * create batches of work (i.e., only receive a notification after several
843e19887f64dde75055cf8842fc4db2171eff45johnlev * messages have been enqueued) then you will need to create a customised
843e19887f64dde75055cf8842fc4db2171eff45johnlev * version of the FINAL_CHECK macro in your own code, which sets the event
843e19887f64dde75055cf8842fc4db2171eff45johnlev * field appropriately.
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do { \
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_wmb(); /* back sees requests /before/ updated producer index */ \
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_mb(); /* back sees new requests /before/ we check req_event */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) < \
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do { \
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_wmb(); /* front sees resps /before/ updated producer index */ \
349b53dd4e695e3d833b5380540385145b2d3ae8Stuart Maybee xen_mb(); /* front sees new resps /before/ we check rsp_event */ \
843e19887f64dde75055cf8842fc4db2171eff45johnlev (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) < \
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define RING_FINAL_CHECK_FOR_REQUESTS(_r, _work_to_do) do { \
843e19887f64dde75055cf8842fc4db2171eff45johnlev if (_work_to_do) break; \
843e19887f64dde75055cf8842fc4db2171eff45johnlev#define RING_FINAL_CHECK_FOR_RESPONSES(_r, _work_to_do) do { \
843e19887f64dde75055cf8842fc4db2171eff45johnlev (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
843e19887f64dde75055cf8842fc4db2171eff45johnlev if (_work_to_do) break; \
843e19887f64dde75055cf8842fc4db2171eff45johnlev (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r); \
843e19887f64dde75055cf8842fc4db2171eff45johnlev#endif /* __XEN_PUBLIC_IO_RING_H__ */
843e19887f64dde75055cf8842fc4db2171eff45johnlev * Local variables:
843e19887f64dde75055cf8842fc4db2171eff45johnlev * c-set-style: "BSD"
843e19887f64dde75055cf8842fc4db2171eff45johnlev * c-basic-offset: 4
843e19887f64dde75055cf8842fc4db2171eff45johnlev * tab-width: 4
843e19887f64dde75055cf8842fc4db2171eff45johnlev * indent-tabs-mode: nil