// SPDX-License-Identifier: BSD-3-Clause
/*
 * Copyright (c) 2009-2012,2016,2023 Microsoft Corp.
 * Copyright (c) 2012 NetApp Inc.
 * Copyright (c) 2012 Citrix Inc.
 * All rights reserved.
 */

#include <errno.h>
#include <fcntl.h>
#include <emmintrin.h>
#include <linux/limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include <unistd.h>
#include "vmbus_bufring.h"

/**
 * Compiler barrier.
 *
 * Guarantees that operation reordering does not occur at compile time
 * for operations directly before and after the barrier.
 */
#define rte_compiler_barrier()          ({ asm volatile ("" : : : "memory"); })

#define VMBUS_RQST_ERROR        0xFFFFFFFFFFFFFFFF
#define ALIGN(val, align)       ((typeof(val))((val) & (~((typeof(val))((align) - 1)))))

void *vmbus_uio_map(int *fd, int size)
{
        void *map;

        map = mmap(NULL, 2 * size, PROT_READ | PROT_WRITE, MAP_SHARED, *fd, 0);
        if (map == MAP_FAILED)
                return NULL;

        return map;
}

/* Increase bufring index by inc with wraparound */
static inline uint32_t vmbus_br_idxinc(uint32_t idx, uint32_t inc, uint32_t sz)
{
        idx += inc;
        if (idx >= sz)
                idx -= sz;

        return idx;
}

void vmbus_br_setup(struct vmbus_br *br, void *buf, unsigned int blen)
{
        br->vbr = buf;
        br->windex = br->vbr->windex;
        br->dsize = blen - sizeof(struct vmbus_bufring);
}

static inline __always_inline void
rte_smp_mb(void)
{
        asm volatile("lock addl $0, -128(%%rsp); " ::: "memory");
}

static inline int
rte_atomic32_cmpset(volatile uint32_t *dst, uint32_t exp, uint32_t src)
{
        uint8_t res;

        asm volatile("lock ; "
                     "cmpxchgl %[src], %[dst];"
                     "sete %[res];"
                     : [res] "=a" (res),     /* output */
                     [dst] "=m" (*dst)
                     : [src] "r" (src),      /* input */
                     "a" (exp),
                     "m" (*dst)
                     : "memory");            /* no-clobber list */
        return res;
}

static inline uint32_t
vmbus_txbr_copyto(const struct vmbus_br *tbr, uint32_t windex,
                  const void *src0, uint32_t cplen)
{
        uint8_t *br_data = tbr->vbr->data;
        uint32_t br_dsize = tbr->dsize;
        const uint8_t *src = src0;

        /* XXX use double mapping like Linux kernel? */
        if (cplen > br_dsize - windex) {
                uint32_t fraglen = br_dsize - windex;

                /* Wrap-around detected */
                memcpy(br_data + windex, src, fraglen);
                memcpy(br_data, src + fraglen, cplen - fraglen);
        } else {
                memcpy(br_data + windex, src, cplen);
        }

        return vmbus_br_idxinc(windex, cplen, br_dsize);
}

/*
 * Write scattered channel packet to TX bufring.
 *
 * The offset of this channel packet is written as a 64bits value
 * immediately after this channel packet.
 *
 * The write goes through three stages:
 *  1. Reserve space in ring buffer for the new data.
 *     Writer atomically moves priv_write_index.
 *  2. Copy the new data into the ring.
 *  3. Update the tail of the ring (visible to host) that indicates
 *     next read location. Writer updates write_index
 */
static int
vmbus_txbr_write(struct vmbus_br *tbr, const struct iovec iov[], int iovlen)
{
        struct vmbus_bufring *vbr = tbr->vbr;
        uint32_t ring_size = tbr->dsize;
        uint32_t old_windex, next_windex, windex, total;
        uint64_t save_windex;
        int i;

        total = 0;
        for (i = 0; i < iovlen; i++)
                total += iov[i].iov_len;
        total += sizeof(save_windex);

        /* Reserve space in ring */
        do {
                uint32_t avail;

                /* Get current free location */
                old_windex = tbr->windex;

                /* Prevent compiler reordering this with calculation */
                rte_compiler_barrier();

                avail = vmbus_br_availwrite(tbr, old_windex);

                /* If not enough space in ring, then tell caller. */
                if (avail <= total)
                        return -EAGAIN;

                next_windex = vmbus_br_idxinc(old_windex, total, ring_size);

                /* Atomic update of next write_index for other threads */
        } while (!rte_atomic32_cmpset(&tbr->windex, old_windex, next_windex));

        /* Space from old..new is now reserved */
        windex = old_windex;
        for (i = 0; i < iovlen; i++)
                windex = vmbus_txbr_copyto(tbr, windex, iov[i].iov_base, iov[i].iov_len);

        /* Set the offset of the current channel packet. */
        save_windex = ((uint64_t)old_windex) << 32;
        windex = vmbus_txbr_copyto(tbr, windex, &save_windex,
                                   sizeof(save_windex));

        /* The region reserved should match region used */
        if (windex != next_windex)
                return -EINVAL;

        /* Ensure that data is available before updating host index */
        rte_compiler_barrier();

        /* Checkin for our reservation. wait for our turn to update host */
        while (!rte_atomic32_cmpset(&vbr->windex, old_windex, next_windex))
                _mm_pause();

        return 0;
}

int rte_vmbus_chan_send(struct vmbus_br *txbr, uint16_t type, void *data,
                        uint32_t dlen, uint32_t flags)
{
        struct vmbus_chanpkt pkt;
        unsigned int pktlen, pad_pktlen;
        const uint32_t hlen = sizeof(pkt);
        uint64_t pad = 0;
        struct iovec iov[3];
        int error;

        pktlen = hlen + dlen;
        pad_pktlen = ALIGN(pktlen, sizeof(uint64_t));

        pkt.hdr.type = type;
        pkt.hdr.flags = flags;
        pkt.hdr.hlen = hlen >> VMBUS_CHANPKT_SIZE_SHIFT;
        pkt.hdr.tlen = pad_pktlen >> VMBUS_CHANPKT_SIZE_SHIFT;
        pkt.hdr.xactid = VMBUS_RQST_ERROR;

        iov[0].iov_base = &pkt;
        iov[0].iov_len = hlen;
        iov[1].iov_base = data;
        iov[1].iov_len = dlen;
        iov[2].iov_base = &pad;
        iov[2].iov_len = pad_pktlen - pktlen;

        error = vmbus_txbr_write(txbr, iov, 3);

        return error;
}

static inline uint32_t
vmbus_rxbr_copyfrom(const struct vmbus_br *rbr, uint32_t rindex,
                    void *dst0, size_t cplen)
{
        const uint8_t *br_data = rbr->vbr->data;
        uint32_t br_dsize = rbr->dsize;
        uint8_t *dst = dst0;

        if (cplen > br_dsize - rindex) {
                uint32_t fraglen = br_dsize - rindex;

                /* Wrap-around detected. */
                memcpy(dst, br_data + rindex, fraglen);
                memcpy(dst + fraglen, br_data, cplen - fraglen);
        } else {
                memcpy(dst, br_data + rindex, cplen);
        }

        return vmbus_br_idxinc(rindex, cplen, br_dsize);
}

/* Copy data from receive ring but don't change index */
static int
vmbus_rxbr_peek(const struct vmbus_br *rbr, void *data, size_t dlen)
{
        uint32_t avail;

        /*
         * The requested data and the 64bits channel packet
         * offset should be there at least.
         */
        avail = vmbus_br_availread(rbr);
        if (avail < dlen + sizeof(uint64_t))
                return -EAGAIN;

        vmbus_rxbr_copyfrom(rbr, rbr->vbr->rindex, data, dlen);
        return 0;
}

/*
 * Copy data from receive ring and change index
 * NOTE:
 * We assume (dlen + skip) == sizeof(channel packet).
 */
static int
vmbus_rxbr_read(struct vmbus_br *rbr, void *data, size_t dlen, size_t skip)
{
        struct vmbus_bufring *vbr = rbr->vbr;
        uint32_t br_dsize = rbr->dsize;
        uint32_t rindex;

        if (vmbus_br_availread(rbr) < dlen + skip + sizeof(uint64_t))
                return -EAGAIN;

        /* Record where host was when we started read (for debug) */
        rbr->windex = rbr->vbr->windex;

        /*
         * Copy channel packet from RX bufring.
         */
        rindex = vmbus_br_idxinc(rbr->vbr->rindex, skip, br_dsize);
        rindex = vmbus_rxbr_copyfrom(rbr, rindex, data, dlen);

        /*
         * Discard this channel packet's 64bits offset, which is useless to us.
         */
        rindex = vmbus_br_idxinc(rindex, sizeof(uint64_t), br_dsize);

        /* Update the read index _after_ the channel packet is fetched.  */
        rte_compiler_barrier();

        vbr->rindex = rindex;

        return 0;
}

int rte_vmbus_chan_recv_raw(struct vmbus_br *rxbr,
                            void *data, uint32_t *len)
{
        struct vmbus_chanpkt_hdr pkt;
        uint32_t dlen, bufferlen = *len;
        int error;

        error = vmbus_rxbr_peek(rxbr, &pkt, sizeof(pkt));
        if (error)
                return error;

        if (unlikely(pkt.hlen < VMBUS_CHANPKT_HLEN_MIN))
                /* XXX this channel is dead actually. */
                return -EIO;

        if (unlikely(pkt.hlen > pkt.tlen))
                return -EIO;

        /* Length are in quad words */
        dlen = pkt.tlen << VMBUS_CHANPKT_SIZE_SHIFT;
        *len = dlen;

        /* If caller buffer is not large enough */
        if (unlikely(dlen > bufferlen))
                return -ENOBUFS;

        /* Read data and skip packet header */
        error = vmbus_rxbr_read(rxbr, data, dlen, 0);
        if (error)
                return error;

        /* Return the number of bytes read */
        return dlen + sizeof(uint64_t);
}