printf: Remove unused 'bprintf'

[drm/drm-misc.git] / kernel / bpf / ringbuf.c

#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/err.h>
#include <linux/irq_work.h>
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <linux/kmemleak.h>
#include <uapi/linux/btf.h>
#include <linux/btf_ids.h>

#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)

/* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */
#define RINGBUF_PGOFF \
        (offsetof(struct bpf_ringbuf, consumer_pos) >> PAGE_SHIFT)
/* consumer page and producer page */
#define RINGBUF_POS_PAGES 2
#define RINGBUF_NR_META_PAGES (RINGBUF_PGOFF + RINGBUF_POS_PAGES)

#define RINGBUF_MAX_RECORD_SZ (UINT_MAX/4)

struct bpf_ringbuf {
        wait_queue_head_t waitq;
        struct irq_work work;
        u64 mask;
        struct page **pages;
        int nr_pages;
        raw_spinlock_t spinlock ____cacheline_aligned_in_smp;
        /* For user-space producer ring buffers, an atomic_t busy bit is used
         * to synchronize access to the ring buffers in the kernel, rather than
         * the spinlock that is used for kernel-producer ring buffers. This is
         * done because the ring buffer must hold a lock across a BPF program's
         * callback:
         *
         *    __bpf_user_ringbuf_peek() // lock acquired
         * -> program callback_fn()
         * -> __bpf_user_ringbuf_sample_release() // lock released
         *
         * It is unsafe and incorrect to hold an IRQ spinlock across what could
         * be a long execution window, so we instead simply disallow concurrent
         * access to the ring buffer by kernel consumers, and return -EBUSY from
         * __bpf_user_ringbuf_peek() if the busy bit is held by another task.
         */
        atomic_t busy ____cacheline_aligned_in_smp;
        /* Consumer and producer counters are put into separate pages to
         * allow each position to be mapped with different permissions.
         * This prevents a user-space application from modifying the
         * position and ruining in-kernel tracking. The permissions of the
         * pages depend on who is producing samples: user-space or the
         * kernel. Note that the pending counter is placed in the same
         * page as the producer, so that it shares the same cache line.
         *
         * Kernel-producer
         * ---------------
         * The producer position and data pages are mapped as r/o in
         * userspace. For this approach, bits in the header of samples are
         * used to signal to user-space, and to other producers, whether a
         * sample is currently being written.
         *
         * User-space producer
         * -------------------
         * Only the page containing the consumer position is mapped r/o in
         * user-space. User-space producers also use bits of the header to
         * communicate to the kernel, but the kernel must carefully check and
         * validate each sample to ensure that they're correctly formatted, and
         * fully contained within the ring buffer.
         */
        unsigned long consumer_pos __aligned(PAGE_SIZE);
        unsigned long producer_pos __aligned(PAGE_SIZE);
        unsigned long pending_pos;
        char data[] __aligned(PAGE_SIZE);
};

struct bpf_ringbuf_map {
        struct bpf_map map;
        struct bpf_ringbuf *rb;
};

/* 8-byte ring buffer record header structure */
struct bpf_ringbuf_hdr {
        u32 len;
        u32 pg_off;
};

static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
{
        const gfp_t flags = GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL |
                            __GFP_NOWARN | __GFP_ZERO;
        int nr_meta_pages = RINGBUF_NR_META_PAGES;
        int nr_data_pages = data_sz >> PAGE_SHIFT;
        int nr_pages = nr_meta_pages + nr_data_pages;
        struct page **pages, *page;
        struct bpf_ringbuf *rb;
        size_t array_size;
        int i;

        /* Each data page is mapped twice to allow "virtual"
         * continuous read of samples wrapping around the end of ring
         * buffer area:
         * ------------------------------------------------------
         * | meta pages |  real data pages  |  same data pages  |
         * ------------------------------------------------------
         * |            | 1 2 3 4 5 6 7 8 9 | 1 2 3 4 5 6 7 8 9 |
         * ------------------------------------------------------
         * |            | TA             DA | TA             DA |
         * ------------------------------------------------------
         *                               ^^^^^^^
         *                                  |
         * Here, no need to worry about special handling of wrapped-around
         * data due to double-mapped data pages. This works both in kernel and
         * when mmap()'ed in user-space, simplifying both kernel and
         * user-space implementations significantly.
         */
        array_size = (nr_meta_pages + 2 * nr_data_pages) * sizeof(*pages);
        pages = bpf_map_area_alloc(array_size, numa_node);
        if (!pages)
                return NULL;

        for (i = 0; i < nr_pages; i++) {
                page = alloc_pages_node(numa_node, flags, 0);
                if (!page) {
                        nr_pages = i;
                        goto err_free_pages;
                }
                pages[i] = page;
                if (i >= nr_meta_pages)
                        pages[nr_data_pages + i] = page;
        }

        rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
                  VM_MAP | VM_USERMAP, PAGE_KERNEL);
        if (rb) {
                kmemleak_not_leak(pages);
                rb->pages = pages;
                rb->nr_pages = nr_pages;
                return rb;
        }

err_free_pages:
        for (i = 0; i < nr_pages; i++)
                __free_page(pages[i]);
        bpf_map_area_free(pages);
        return NULL;
}

static void bpf_ringbuf_notify(struct irq_work *work)
{
        struct bpf_ringbuf *rb = container_of(work, struct bpf_ringbuf, work);

        wake_up_all(&rb->waitq);
}

/* Maximum size of ring buffer area is limited by 32-bit page offset within
 * record header, counted in pages. Reserve 8 bits for extensibility, and
 * take into account few extra pages for consumer/producer pages and
 * non-mmap()'able parts, the current maximum size would be:
 *
 *     (((1ULL << 24) - RINGBUF_POS_PAGES - RINGBUF_PGOFF) * PAGE_SIZE)
 *
 * This gives 64GB limit, which seems plenty for single ring buffer. Now
 * considering that the maximum value of data_sz is (4GB - 1), there
 * will be no overflow, so just note the size limit in the comments.
 */
static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
{
        struct bpf_ringbuf *rb;

        rb = bpf_ringbuf_area_alloc(data_sz, numa_node);
        if (!rb)
                return NULL;

        raw_spin_lock_init(&rb->spinlock);
        atomic_set(&rb->busy, 0);
        init_waitqueue_head(&rb->waitq);
        init_irq_work(&rb->work, bpf_ringbuf_notify);

        rb->mask = data_sz - 1;
        rb->consumer_pos = 0;
        rb->producer_pos = 0;
        rb->pending_pos = 0;

        return rb;
}

static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
{
        struct bpf_ringbuf_map *rb_map;

        if (attr->map_flags & ~RINGBUF_CREATE_FLAG_MASK)
                return ERR_PTR(-EINVAL);

        if (attr->key_size || attr->value_size ||
            !is_power_of_2(attr->max_entries) ||
            !PAGE_ALIGNED(attr->max_entries))
                return ERR_PTR(-EINVAL);

        rb_map = bpf_map_area_alloc(sizeof(*rb_map), NUMA_NO_NODE);
        if (!rb_map)
                return ERR_PTR(-ENOMEM);

        bpf_map_init_from_attr(&rb_map->map, attr);

        rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node);
        if (!rb_map->rb) {
                bpf_map_area_free(rb_map);
                return ERR_PTR(-ENOMEM);
        }

        return &rb_map->map;
}

static void bpf_ringbuf_free(struct bpf_ringbuf *rb)
{
        /* copy pages pointer and nr_pages to local variable, as we are going
         * to unmap rb itself with vunmap() below
         */
        struct page **pages = rb->pages;
        int i, nr_pages = rb->nr_pages;

        vunmap(rb);
        for (i = 0; i < nr_pages; i++)
                __free_page(pages[i]);
        bpf_map_area_free(pages);
}

static void ringbuf_map_free(struct bpf_map *map)
{
        struct bpf_ringbuf_map *rb_map;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);
        bpf_ringbuf_free(rb_map->rb);
        bpf_map_area_free(rb_map);
}

static void *ringbuf_map_lookup_elem(struct bpf_map *map, void *key)
{
        return ERR_PTR(-ENOTSUPP);
}

static long ringbuf_map_update_elem(struct bpf_map *map, void *key, void *value,
                                    u64 flags)
{
        return -ENOTSUPP;
}

static long ringbuf_map_delete_elem(struct bpf_map *map, void *key)
{
        return -ENOTSUPP;
}

static int ringbuf_map_get_next_key(struct bpf_map *map, void *key,
                                    void *next_key)
{
        return -ENOTSUPP;
}

static int ringbuf_map_mmap_kern(struct bpf_map *map, struct vm_area_struct *vma)
{
        struct bpf_ringbuf_map *rb_map;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);

        if (vma->vm_flags & VM_WRITE) {
                /* allow writable mapping for the consumer_pos only */
                if (vma->vm_pgoff != 0 || vma->vm_end - vma->vm_start != PAGE_SIZE)
                        return -EPERM;
        } else {
                vm_flags_clear(vma, VM_MAYWRITE);
        }
        /* remap_vmalloc_range() checks size and offset constraints */
        return remap_vmalloc_range(vma, rb_map->rb,
                                   vma->vm_pgoff + RINGBUF_PGOFF);
}

static int ringbuf_map_mmap_user(struct bpf_map *map, struct vm_area_struct *vma)
{
        struct bpf_ringbuf_map *rb_map;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);

        if (vma->vm_flags & VM_WRITE) {
                if (vma->vm_pgoff == 0)
                        /* Disallow writable mappings to the consumer pointer,
                         * and allow writable mappings to both the producer
                         * position, and the ring buffer data itself.
                         */
                        return -EPERM;
        } else {
                vm_flags_clear(vma, VM_MAYWRITE);
        }
        /* remap_vmalloc_range() checks size and offset constraints */
        return remap_vmalloc_range(vma, rb_map->rb, vma->vm_pgoff + RINGBUF_PGOFF);
}

static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb)
{
        unsigned long cons_pos, prod_pos;

        cons_pos = smp_load_acquire(&rb->consumer_pos);
        prod_pos = smp_load_acquire(&rb->producer_pos);
        return prod_pos - cons_pos;
}

static u32 ringbuf_total_data_sz(const struct bpf_ringbuf *rb)
{
        return rb->mask + 1;
}

static __poll_t ringbuf_map_poll_kern(struct bpf_map *map, struct file *filp,
                                      struct poll_table_struct *pts)
{
        struct bpf_ringbuf_map *rb_map;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);
        poll_wait(filp, &rb_map->rb->waitq, pts);

        if (ringbuf_avail_data_sz(rb_map->rb))
                return EPOLLIN | EPOLLRDNORM;
        return 0;
}

static __poll_t ringbuf_map_poll_user(struct bpf_map *map, struct file *filp,
                                      struct poll_table_struct *pts)
{
        struct bpf_ringbuf_map *rb_map;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);
        poll_wait(filp, &rb_map->rb->waitq, pts);

        if (ringbuf_avail_data_sz(rb_map->rb) < ringbuf_total_data_sz(rb_map->rb))
                return EPOLLOUT | EPOLLWRNORM;
        return 0;
}

static u64 ringbuf_map_mem_usage(const struct bpf_map *map)
{
        struct bpf_ringbuf *rb;
        int nr_data_pages;
        int nr_meta_pages;
        u64 usage = sizeof(struct bpf_ringbuf_map);

        rb = container_of(map, struct bpf_ringbuf_map, map)->rb;
        usage += (u64)rb->nr_pages << PAGE_SHIFT;
        nr_meta_pages = RINGBUF_NR_META_PAGES;
        nr_data_pages = map->max_entries >> PAGE_SHIFT;
        usage += (nr_meta_pages + 2 * nr_data_pages) * sizeof(struct page *);
        return usage;
}

BTF_ID_LIST_SINGLE(ringbuf_map_btf_ids, struct, bpf_ringbuf_map)
const struct bpf_map_ops ringbuf_map_ops = {
        .map_meta_equal = bpf_map_meta_equal,
        .map_alloc = ringbuf_map_alloc,
        .map_free = ringbuf_map_free,
        .map_mmap = ringbuf_map_mmap_kern,
        .map_poll = ringbuf_map_poll_kern,
        .map_lookup_elem = ringbuf_map_lookup_elem,
        .map_update_elem = ringbuf_map_update_elem,
        .map_delete_elem = ringbuf_map_delete_elem,
        .map_get_next_key = ringbuf_map_get_next_key,
        .map_mem_usage = ringbuf_map_mem_usage,
        .map_btf_id = &ringbuf_map_btf_ids[0],
};

BTF_ID_LIST_SINGLE(user_ringbuf_map_btf_ids, struct, bpf_ringbuf_map)
const struct bpf_map_ops user_ringbuf_map_ops = {
        .map_meta_equal = bpf_map_meta_equal,
        .map_alloc = ringbuf_map_alloc,
        .map_free = ringbuf_map_free,
        .map_mmap = ringbuf_map_mmap_user,
        .map_poll = ringbuf_map_poll_user,
        .map_lookup_elem = ringbuf_map_lookup_elem,
        .map_update_elem = ringbuf_map_update_elem,
        .map_delete_elem = ringbuf_map_delete_elem,
        .map_get_next_key = ringbuf_map_get_next_key,
        .map_mem_usage = ringbuf_map_mem_usage,
        .map_btf_id = &user_ringbuf_map_btf_ids[0],
};

/* Given pointer to ring buffer record metadata and struct bpf_ringbuf itself,
 * calculate offset from record metadata to ring buffer in pages, rounded
 * down. This page offset is stored as part of record metadata and allows to
 * restore struct bpf_ringbuf * from record pointer. This page offset is
 * stored at offset 4 of record metadata header.
 */
static size_t bpf_ringbuf_rec_pg_off(struct bpf_ringbuf *rb,
                                     struct bpf_ringbuf_hdr *hdr)
{
        return ((void *)hdr - (void *)rb) >> PAGE_SHIFT;
}

/* Given pointer to ring buffer record header, restore pointer to struct
 * bpf_ringbuf itself by using page offset stored at offset 4
 */
static struct bpf_ringbuf *
bpf_ringbuf_restore_from_rec(struct bpf_ringbuf_hdr *hdr)
{
        unsigned long addr = (unsigned long)(void *)hdr;
        unsigned long off = (unsigned long)hdr->pg_off << PAGE_SHIFT;

        return (void*)((addr & PAGE_MASK) - off);
}

static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
{
        unsigned long cons_pos, prod_pos, new_prod_pos, pend_pos, flags;
        struct bpf_ringbuf_hdr *hdr;
        u32 len, pg_off, tmp_size, hdr_len;

        if (unlikely(size > RINGBUF_MAX_RECORD_SZ))
                return NULL;

        len = round_up(size + BPF_RINGBUF_HDR_SZ, 8);
        if (len > ringbuf_total_data_sz(rb))
                return NULL;

        cons_pos = smp_load_acquire(&rb->consumer_pos);

        if (in_nmi()) {
                if (!raw_spin_trylock_irqsave(&rb->spinlock, flags))
                        return NULL;
        } else {
                raw_spin_lock_irqsave(&rb->spinlock, flags);
        }

        pend_pos = rb->pending_pos;
        prod_pos = rb->producer_pos;
        new_prod_pos = prod_pos + len;

        while (pend_pos < prod_pos) {
                hdr = (void *)rb->data + (pend_pos & rb->mask);
                hdr_len = READ_ONCE(hdr->len);
                if (hdr_len & BPF_RINGBUF_BUSY_BIT)
                        break;
                tmp_size = hdr_len & ~BPF_RINGBUF_DISCARD_BIT;
                tmp_size = round_up(tmp_size + BPF_RINGBUF_HDR_SZ, 8);
                pend_pos += tmp_size;
        }
        rb->pending_pos = pend_pos;

        /* check for out of ringbuf space:
         * - by ensuring producer position doesn't advance more than
         *   (ringbuf_size - 1) ahead
         * - by ensuring oldest not yet committed record until newest
         *   record does not span more than (ringbuf_size - 1)
         */
        if (new_prod_pos - cons_pos > rb->mask ||
            new_prod_pos - pend_pos > rb->mask) {
                raw_spin_unlock_irqrestore(&rb->spinlock, flags);
                return NULL;
        }

        hdr = (void *)rb->data + (prod_pos & rb->mask);
        pg_off = bpf_ringbuf_rec_pg_off(rb, hdr);
        hdr->len = size | BPF_RINGBUF_BUSY_BIT;
        hdr->pg_off = pg_off;

        /* pairs with consumer's smp_load_acquire() */
        smp_store_release(&rb->producer_pos, new_prod_pos);

        raw_spin_unlock_irqrestore(&rb->spinlock, flags);

        return (void *)hdr + BPF_RINGBUF_HDR_SZ;
}

BPF_CALL_3(bpf_ringbuf_reserve, struct bpf_map *, map, u64, size, u64, flags)
{
        struct bpf_ringbuf_map *rb_map;

        if (unlikely(flags))
                return 0;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);
        return (unsigned long)__bpf_ringbuf_reserve(rb_map->rb, size);
}

const struct bpf_func_proto bpf_ringbuf_reserve_proto = {
        .func           = bpf_ringbuf_reserve,
        .ret_type       = RET_PTR_TO_RINGBUF_MEM_OR_NULL,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_CONST_ALLOC_SIZE_OR_ZERO,
        .arg3_type      = ARG_ANYTHING,
};

static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard)
{
        unsigned long rec_pos, cons_pos;
        struct bpf_ringbuf_hdr *hdr;
        struct bpf_ringbuf *rb;
        u32 new_len;

        hdr = sample - BPF_RINGBUF_HDR_SZ;
        rb = bpf_ringbuf_restore_from_rec(hdr);
        new_len = hdr->len ^ BPF_RINGBUF_BUSY_BIT;
        if (discard)
                new_len |= BPF_RINGBUF_DISCARD_BIT;

        /* update record header with correct final size prefix */
        xchg(&hdr->len, new_len);

        /* if consumer caught up and is waiting for our record, notify about
         * new data availability
         */
        rec_pos = (void *)hdr - (void *)rb->data;
        cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask;

        if (flags & BPF_RB_FORCE_WAKEUP)
                irq_work_queue(&rb->work);
        else if (cons_pos == rec_pos && !(flags & BPF_RB_NO_WAKEUP))
                irq_work_queue(&rb->work);
}

BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
{
        bpf_ringbuf_commit(sample, flags, false /* discard */);
        return 0;
}

const struct bpf_func_proto bpf_ringbuf_submit_proto = {
        .func           = bpf_ringbuf_submit,
        .ret_type       = RET_VOID,
        .arg1_type      = ARG_PTR_TO_RINGBUF_MEM | OBJ_RELEASE,
        .arg2_type      = ARG_ANYTHING,
};

BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags)
{
        bpf_ringbuf_commit(sample, flags, true /* discard */);
        return 0;
}

const struct bpf_func_proto bpf_ringbuf_discard_proto = {
        .func           = bpf_ringbuf_discard,
        .ret_type       = RET_VOID,
        .arg1_type      = ARG_PTR_TO_RINGBUF_MEM | OBJ_RELEASE,
        .arg2_type      = ARG_ANYTHING,
};

BPF_CALL_4(bpf_ringbuf_output, struct bpf_map *, map, void *, data, u64, size,
           u64, flags)
{
        struct bpf_ringbuf_map *rb_map;
        void *rec;

        if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
                return -EINVAL;

        rb_map = container_of(map, struct bpf_ringbuf_map, map);
        rec = __bpf_ringbuf_reserve(rb_map->rb, size);
        if (!rec)
                return -EAGAIN;

        memcpy(rec, data, size);
        bpf_ringbuf_commit(rec, flags, false /* discard */);
        return 0;
}

const struct bpf_func_proto bpf_ringbuf_output_proto = {
        .func           = bpf_ringbuf_output,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_MEM | MEM_RDONLY,
        .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
        .arg4_type      = ARG_ANYTHING,
};

BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags)
{
        struct bpf_ringbuf *rb;

        rb = container_of(map, struct bpf_ringbuf_map, map)->rb;

        switch (flags) {
        case BPF_RB_AVAIL_DATA:
                return ringbuf_avail_data_sz(rb);
        case BPF_RB_RING_SIZE:
                return ringbuf_total_data_sz(rb);
        case BPF_RB_CONS_POS:
                return smp_load_acquire(&rb->consumer_pos);
        case BPF_RB_PROD_POS:
                return smp_load_acquire(&rb->producer_pos);
        default:
                return 0;
        }
}

const struct bpf_func_proto bpf_ringbuf_query_proto = {
        .func           = bpf_ringbuf_query,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_ANYTHING,
};

BPF_CALL_4(bpf_ringbuf_reserve_dynptr, struct bpf_map *, map, u32, size, u64, flags,
           struct bpf_dynptr_kern *, ptr)
{
        struct bpf_ringbuf_map *rb_map;
        void *sample;
        int err;

        if (unlikely(flags)) {
                bpf_dynptr_set_null(ptr);
                return -EINVAL;
        }

        err = bpf_dynptr_check_size(size);
        if (err) {
                bpf_dynptr_set_null(ptr);
                return err;
        }

        rb_map = container_of(map, struct bpf_ringbuf_map, map);

        sample = __bpf_ringbuf_reserve(rb_map->rb, size);
        if (!sample) {
                bpf_dynptr_set_null(ptr);
                return -EINVAL;
        }

        bpf_dynptr_init(ptr, sample, BPF_DYNPTR_TYPE_RINGBUF, 0, size);

        return 0;
}

const struct bpf_func_proto bpf_ringbuf_reserve_dynptr_proto = {
        .func           = bpf_ringbuf_reserve_dynptr,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_ANYTHING,
        .arg3_type      = ARG_ANYTHING,
        .arg4_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | MEM_UNINIT | MEM_WRITE,
};

BPF_CALL_2(bpf_ringbuf_submit_dynptr, struct bpf_dynptr_kern *, ptr, u64, flags)
{
        if (!ptr->data)
                return 0;

        bpf_ringbuf_commit(ptr->data, flags, false /* discard */);

        bpf_dynptr_set_null(ptr);

        return 0;
}

const struct bpf_func_proto bpf_ringbuf_submit_dynptr_proto = {
        .func           = bpf_ringbuf_submit_dynptr,
        .ret_type       = RET_VOID,
        .arg1_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
        .arg2_type      = ARG_ANYTHING,
};

BPF_CALL_2(bpf_ringbuf_discard_dynptr, struct bpf_dynptr_kern *, ptr, u64, flags)
{
        if (!ptr->data)
                return 0;

        bpf_ringbuf_commit(ptr->data, flags, true /* discard */);

        bpf_dynptr_set_null(ptr);

        return 0;
}

const struct bpf_func_proto bpf_ringbuf_discard_dynptr_proto = {
        .func           = bpf_ringbuf_discard_dynptr,
        .ret_type       = RET_VOID,
        .arg1_type      = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
        .arg2_type      = ARG_ANYTHING,
};

static int __bpf_user_ringbuf_peek(struct bpf_ringbuf *rb, void **sample, u32 *size)
{
        int err;
        u32 hdr_len, sample_len, total_len, flags, *hdr;
        u64 cons_pos, prod_pos;

        /* Synchronizes with smp_store_release() in user-space producer. */
        prod_pos = smp_load_acquire(&rb->producer_pos);
        if (prod_pos % 8)
                return -EINVAL;

        /* Synchronizes with smp_store_release() in __bpf_user_ringbuf_sample_release() */
        cons_pos = smp_load_acquire(&rb->consumer_pos);
        if (cons_pos >= prod_pos)
                return -ENODATA;

        hdr = (u32 *)((uintptr_t)rb->data + (uintptr_t)(cons_pos & rb->mask));
        /* Synchronizes with smp_store_release() in user-space producer. */
        hdr_len = smp_load_acquire(hdr);
        flags = hdr_len & (BPF_RINGBUF_BUSY_BIT | BPF_RINGBUF_DISCARD_BIT);
        sample_len = hdr_len & ~flags;
        total_len = round_up(sample_len + BPF_RINGBUF_HDR_SZ, 8);

        /* The sample must fit within the region advertised by the producer position. */
        if (total_len > prod_pos - cons_pos)
                return -EINVAL;

        /* The sample must fit within the data region of the ring buffer. */
        if (total_len > ringbuf_total_data_sz(rb))
                return -E2BIG;

        /* The sample must fit into a struct bpf_dynptr. */
        err = bpf_dynptr_check_size(sample_len);
        if (err)
                return -E2BIG;

        if (flags & BPF_RINGBUF_DISCARD_BIT) {
                /* If the discard bit is set, the sample should be skipped.
                 *
                 * Update the consumer pos, and return -EAGAIN so the caller
                 * knows to skip this sample and try to read the next one.
                 */
                smp_store_release(&rb->consumer_pos, cons_pos + total_len);
                return -EAGAIN;
        }

        if (flags & BPF_RINGBUF_BUSY_BIT)
                return -ENODATA;

        *sample = (void *)((uintptr_t)rb->data +
                           (uintptr_t)((cons_pos + BPF_RINGBUF_HDR_SZ) & rb->mask));
        *size = sample_len;
        return 0;
}

static void __bpf_user_ringbuf_sample_release(struct bpf_ringbuf *rb, size_t size, u64 flags)
{
        u64 consumer_pos;
        u32 rounded_size = round_up(size + BPF_RINGBUF_HDR_SZ, 8);

        /* Using smp_load_acquire() is unnecessary here, as the busy-bit
         * prevents another task from writing to consumer_pos after it was read
         * by this task with smp_load_acquire() in __bpf_user_ringbuf_peek().
         */
        consumer_pos = rb->consumer_pos;
         /* Synchronizes with smp_load_acquire() in user-space producer. */
        smp_store_release(&rb->consumer_pos, consumer_pos + rounded_size);
}

BPF_CALL_4(bpf_user_ringbuf_drain, struct bpf_map *, map,
           void *, callback_fn, void *, callback_ctx, u64, flags)
{
        struct bpf_ringbuf *rb;
        long samples, discarded_samples = 0, ret = 0;
        bpf_callback_t callback = (bpf_callback_t)callback_fn;
        u64 wakeup_flags = BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP;
        int busy = 0;

        if (unlikely(flags & ~wakeup_flags))
                return -EINVAL;

        rb = container_of(map, struct bpf_ringbuf_map, map)->rb;

        /* If another consumer is already consuming a sample, wait for them to finish. */
        if (!atomic_try_cmpxchg(&rb->busy, &busy, 1))
                return -EBUSY;

        for (samples = 0; samples < BPF_MAX_USER_RINGBUF_SAMPLES && ret == 0; samples++) {
                int err;
                u32 size;
                void *sample;
                struct bpf_dynptr_kern dynptr;

                err = __bpf_user_ringbuf_peek(rb, &sample, &size);
                if (err) {
                        if (err == -ENODATA) {
                                break;
                        } else if (err == -EAGAIN) {
                                discarded_samples++;
                                continue;
                        } else {
                                ret = err;
                                goto schedule_work_return;
                        }
                }

                bpf_dynptr_init(&dynptr, sample, BPF_DYNPTR_TYPE_LOCAL, 0, size);
                ret = callback((uintptr_t)&dynptr, (uintptr_t)callback_ctx, 0, 0, 0);
                __bpf_user_ringbuf_sample_release(rb, size, flags);
        }
        ret = samples - discarded_samples;

schedule_work_return:
        /* Prevent the clearing of the busy-bit from being reordered before the
         * storing of any rb consumer or producer positions.
         */
        atomic_set_release(&rb->busy, 0);

        if (flags & BPF_RB_FORCE_WAKEUP)
                irq_work_queue(&rb->work);
        else if (!(flags & BPF_RB_NO_WAKEUP) && samples > 0)
                irq_work_queue(&rb->work);
        return ret;
}

const struct bpf_func_proto bpf_user_ringbuf_drain_proto = {
        .func           = bpf_user_ringbuf_drain,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_FUNC,
        .arg3_type      = ARG_PTR_TO_STACK_OR_NULL,
        .arg4_type      = ARG_ANYTHING,
};