// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
/*
 * Ring buffer operations.
 *
 * Copyright (C) 2020 Facebook, Inc.
 */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <linux/err.h>
#include <linux/bpf.h>
#include <asm/barrier.h>
#include <sys/mman.h>
#include <sys/epoll.h>

#include "libbpf.h"
#include "libbpf_internal.h"
#include "bpf.h"

struct ring {
        ring_buffer_sample_fn sample_cb;
        void *ctx;
        void *data;
        unsigned long *consumer_pos;
        unsigned long *producer_pos;
        unsigned long mask;
        int map_fd;
};

struct ring_buffer {
        struct epoll_event *events;
        struct ring *rings;
        size_t page_size;
        int epoll_fd;
        int ring_cnt;
};

static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)
{
        if (r->consumer_pos) {
                munmap(r->consumer_pos, rb->page_size);
                r->consumer_pos = NULL;
        }
        if (r->producer_pos) {
                munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
                r->producer_pos = NULL;
        }
}

/* Add extra RINGBUF maps to this ring buffer manager */
int ring_buffer__add(struct ring_buffer *rb, int map_fd,
                     ring_buffer_sample_fn sample_cb, void *ctx)
{
        struct bpf_map_info info;
        __u32 len = sizeof(info);
        struct epoll_event *e;
        struct ring *r;
        void *tmp;
        int err;

        memset(&info, 0, sizeof(info));

        err = bpf_obj_get_info_by_fd(map_fd, &info, &len);
        if (err) {
                err = -errno;
                pr_warn("ringbuf: failed to get map info for fd=%d: %d\n",
                        map_fd, err);
                return err;
        }

        if (info.type != BPF_MAP_TYPE_RINGBUF) {
                pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
                        map_fd);
                return -EINVAL;
        }

        tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings));
        if (!tmp)
                return -ENOMEM;
        rb->rings = tmp;

        tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
        if (!tmp)
                return -ENOMEM;
        rb->events = tmp;

        r = &rb->rings[rb->ring_cnt];
        memset(r, 0, sizeof(*r));

        r->map_fd = map_fd;
        r->sample_cb = sample_cb;
        r->ctx = ctx;
        r->mask = info.max_entries - 1;

        /* Map writable consumer page */
        tmp = mmap(NULL, rb->page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
                   map_fd, 0);
        if (tmp == MAP_FAILED) {
                err = -errno;
                pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
                        map_fd, err);
                return err;
        }
        r->consumer_pos = tmp;

        /* Map read-only producer page and data pages. We map twice as big
         * data size to allow simple reading of samples that wrap around the
         * end of a ring buffer. See kernel implementation for details.
         * */
        tmp = mmap(NULL, rb->page_size + 2 * info.max_entries, PROT_READ,
                   MAP_SHARED, map_fd, rb->page_size);
        if (tmp == MAP_FAILED) {
                err = -errno;
                ringbuf_unmap_ring(rb, r);
                pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
                        map_fd, err);
                return err;
        }
        r->producer_pos = tmp;
        r->data = tmp + rb->page_size;

        e = &rb->events[rb->ring_cnt];
        memset(e, 0, sizeof(*e));

        e->events = EPOLLIN;
        e->data.fd = rb->ring_cnt;
        if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
                err = -errno;
                ringbuf_unmap_ring(rb, r);
                pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
                        map_fd, err);
                return err;
        }

        rb->ring_cnt++;
        return 0;
}

void ring_buffer__free(struct ring_buffer *rb)
{
        int i;

        if (!rb)
                return;

        for (i = 0; i < rb->ring_cnt; ++i)
                ringbuf_unmap_ring(rb, &rb->rings[i]);
        if (rb->epoll_fd >= 0)
                close(rb->epoll_fd);

        free(rb->events);
        free(rb->rings);
        free(rb);
}

struct ring_buffer *
ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx,
                 const struct ring_buffer_opts *opts)
{
        struct ring_buffer *rb;
        int err;

        if (!OPTS_VALID(opts, ring_buffer_opts))
                return NULL;

        rb = calloc(1, sizeof(*rb));
        if (!rb)
                return NULL;

        rb->page_size = getpagesize();

        rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
        if (rb->epoll_fd < 0) {
                err = -errno;
                pr_warn("ringbuf: failed to create epoll instance: %d\n", err);
                goto err_out;
        }

        err = ring_buffer__add(rb, map_fd, sample_cb, ctx);
        if (err)
                goto err_out;

        return rb;

err_out:
        ring_buffer__free(rb);
        return NULL;
}

static inline int roundup_len(__u32 len)
{
        /* clear out top 2 bits (discard and busy, if set) */
        len <<= 2;
        len >>= 2;
        /* add length prefix */
        len += BPF_RINGBUF_HDR_SZ;
        /* round up to 8 byte alignment */
        return (len + 7) / 8 * 8;
}

static int64_t ringbuf_process_ring(struct ring* r)
{
        int *len_ptr, len, err;
        /* 64-bit to avoid overflow in case of extreme application behavior */
        int64_t cnt = 0;
        unsigned long cons_pos, prod_pos;
        bool got_new_data;
        void *sample;

        cons_pos = smp_load_acquire(r->consumer_pos);
        do {
                got_new_data = false;
                prod_pos = smp_load_acquire(r->producer_pos);
                while (cons_pos < prod_pos) {
                        len_ptr = r->data + (cons_pos & r->mask);
                        len = smp_load_acquire(len_ptr);

                        /* sample not committed yet, bail out for now */
                        if (len & BPF_RINGBUF_BUSY_BIT)
                                goto done;

                        got_new_data = true;
                        cons_pos += roundup_len(len);

                        if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
                                sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
                                err = r->sample_cb(r->ctx, sample, len);
                                if (err < 0) {
                                        /* update consumer pos and bail out */
                                        smp_store_release(r->consumer_pos,
                                                          cons_pos);
                                        return err;
                                }
                                cnt++;
                        }

                        smp_store_release(r->consumer_pos, cons_pos);
                }
        } while (got_new_data);
done:
        return cnt;
}

/* Consume available ring buffer(s) data without event polling.
 * Returns number of records consumed across all registered ring buffers (or
 * INT_MAX, whichever is less), or negative number if any of the callbacks
 * return error.
 */
int ring_buffer__consume(struct ring_buffer *rb)
{
        int64_t err, res = 0;
        int i;

        for (i = 0; i < rb->ring_cnt; i++) {
                struct ring *ring = &rb->rings[i];

                err = ringbuf_process_ring(ring);
                if (err < 0)
                        return err;
                res += err;
        }
        if (res > INT_MAX)
                return INT_MAX;
        return res;
}

/* Poll for available data and consume records, if any are available.
 * Returns number of records consumed (or INT_MAX, whichever is less), or
 * negative number, if any of the registered callbacks returned error.
 */
int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
{
        int i, cnt;
        int64_t err, res = 0;

        cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
        if (cnt < 0)
                return -errno;

        for (i = 0; i < cnt; i++) {
                __u32 ring_id = rb->events[i].data.fd;
                struct ring *ring = &rb->rings[ring_id];

                err = ringbuf_process_ring(ring);
                if (err < 0)
                        return err;
                res += err;
        }
        if (res > INT_MAX)
                return INT_MAX;
        return res;
}

/* Get an fd that can be used to sleep until data is available in the ring(s) */
int ring_buffer__epoll_fd(const struct ring_buffer *rb)
{
        return rb->epoll_fd;
}