    /* 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.h"
    #include "../xen-compat.h"

    /* Some PV I/O interfaces need a compatibility variant. */
    #if __XEN_INTERFACE_VERSION__ < 0x00041300
    #define XENPV_FLEX_ARRAY_DIM  1 /* variable size */
    #else
    #define XENPV_FLEX_ARRAY_DIM  XEN_FLEX_ARRAY_DIM
    #endif

    #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) & 0x00000002U) ? 0x2                     : ((x) & 0x1))
    #define __RD4(x)  (((x) & 0x0000000cU) ? __RD2((x) >> 2) << 2    : __RD2(x))
    #define __RD8(x)  (((x) & 0x000000f0U) ? __RD4((x) >> 4) << 4    : __RD4(x))
    #define __RD16(x) (((x) & 0x0000ff00U) ? __RD8((x) >> 8) << 8    : __RD8(x))
    #define __RD32(x) (((x) & 0xffff0000U) ? __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;                                       \
        union {                                                             \
            struct {                                                        \
                uint8_t smartpoll_active;                                   \
            } netif;                                                        \
            struct {                                                        \
                uint8_t msg;                                                \
            } tapif_user;                                                   \
            uint8_t pvt_pad[4];                                             \
        } pvt;                                                              \
        uint8_t __pad[44];                                                  \
        union __name##_sring_entry ring[XENPV_FLEX_ARRAY_DIM];              \
    };                                                                      \
                                                                            \
    /* "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)->pvt.pvt_pad, 0, sizeof((_s)->pvt.pvt_pad));      \
        (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)

    #ifdef __GNUC__
    #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;                                              \
    })
    #else
    /* Same as above, but without the nice GCC ({ ... }) syntax. */
    #define XEN_RING_NR_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

    #ifdef XEN_RING_HAS_UNCONSUMED_IS_BOOL
    /*
     * These variants should only be used in case no caller is abusing them for
     * obtaining the number of unconsumed responses/requests.
     */
    #define RING_HAS_UNCONSUMED_RESPONSES(_r) \
        (!!XEN_RING_NR_UNCONSUMED_RESPONSES(_r))
    #define RING_HAS_UNCONSUMED_REQUESTS(_r)  \
        (!!XEN_RING_NR_UNCONSUMED_REQUESTS(_r))
    #else
    #define RING_HAS_UNCONSUMED_RESPONSES(_r) XEN_RING_NR_UNCONSUMED_RESPONSES(_r)
    #define RING_HAS_UNCONSUMED_REQUESTS(_r)  XEN_RING_NR_UNCONSUMED_REQUESTS(_r)
    #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))

    /*
     * 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 {                                     \
        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)

    /*
     * 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[XEN_FLEX_ARRAY_DIM];                                      \
    };                                                                            \
    DEFINE_XEN_FLEX_RING(name)

    #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:
     */