Ebpf map question

Ebpf map question

[Marco]

Hi

Assuming to have this struct:

struct hash_elem {
    int cnt;
    };

and kernel space program want read cnt value:

struct hash_elem *val = bpf_map_lookup_elem(&hash_map, &key);

    if (val)
   {

# time fraction

    bpf_printk("My value %d", val->cnt);
    }

What happens if the hash_map is a pinned map and in the same time
space of 'time fraction" a user program deletes the element of the
key?
What happen at val pointer?


Thanks.

Marco

Re: Ebpf map question

[Toke Høiland-Jørgensen]

Marco <ctxspi@gmail.com> writes:

> Hi
>
> Assuming to have this struct:
>
> struct hash_elem {
>     int cnt;
>     };
>
> and kernel space program want read cnt value:
>
> struct hash_elem *val = bpf_map_lookup_elem(&hash_map, &key);
>
>     if (val)
>    {
>
> # time fraction
>
>     bpf_printk("My value %d", val->cnt);
>     }
>
> What happens if the hash_map is a pinned map and in the same time
> space of 'time fraction" a user program deletes the element of the
> key?
> What happen at val pointer?

The val pointer is RCU-protected so it will stick around until the end
of your BPF program's execution. However, it's up to your own code to
protect against concurrent *updates* of the value...

-Toke