Helper function `bpf_map_peek_elem`

v4.20

Definition

Copyright (c) 2015 The Libbpf Authors. All rights reserved.

Get an element from map without removing it.

Returns

0 on success, or a negative error in case of failure.

static long (* const bpf_map_peek_elem)(void *map, void *value) = (void *) 89;

Usage

Docs could be improved

This part of the docs is incomplete, contributions are very welcome

Program types

This helper call can be used in the following program types:

Map types

This helper call can be used with the following map types:

Example

#include <vmlinux.h>
#include <bpf/bpf_helpers.h>

#define TC_ACT_OK 0

struct {
   __uint(type, BPF_MAP_TYPE_QUEUE);
   __uint(max_entries, 8);
   __uint(value_size, sizeof(__u32));
} ingress SEC(".maps");

SEC("tc")
int tc_ingress(struct __sk_buff *skb)
{
    void* data_end = (void *)(long)skb->data_end;
    void* data = (void *)(long)skb->data;
    u32 value;
    int err;

    struct ethhdr* eth = (struct ethhdr *)data;
    if ((void *)(eth + 1) > data_end)
        return TC_ACT_OK;

    struct iphdr* iph = (struct iphdr *)(eth + 1);
    if ((void *)(iph + 1) > data_end)
        return TC_ACT_OK;  // Check IP header

    err = bpf_map_push_elem(&ingress, &iph->saddr, 0);
    bpf_printk("Pushed something to queue");
    if (err)
        return TC_ACT_OK;

    err = bpf_map_peek_elem(&ingress, &value); 
    bpf_printk("Peeked at something in queue");
    if (err)
        return TC_ACT_OK;

    if(value == iph->saddr)
    {
        err = bpf_map_pop_elem(&ingress, &value);
        bpf_printk("Popped something from queue");
        if (err)
            return TC_ACT_OK;
   }
   return TC_ACT_OK;
}
char _license[] SEC("license") = "GPL";

Helper function bpf_map_peek_elem