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__ */