Re: Re: [Question] Failed to load ebpf program with BTF-defined map

["Toke Høiland-Jørgensen" <toke@kernel.org>]

wuzongyo@mail.ustc.edu.cn writes:

>> wuzongyo@mail.ustc.edu.cn writes:
>> 
>> > Hi,
>> >
>> > I wrote a simple tc-bpf program like that:
>> >
>> >     #include <linux/bpf.h>
>> >     #include <linux/pkt_cls.h>
>> >     #include <linx/types.h>
>> >     #include <bpf/bpf_helpers.h>
>> >
>> >     struct {
>> >         __uint(type, BPF_MAP_TYPE_HASH);
>> >         __uint(max_entries, 1);
>> >         __type(key, int);
>> >         __type(value, int);
>> >     } hmap SEC(".maps");
>> >
>> >     SEC("classifier")
>> >     int _classifier(struct __sk_buff *skb)
>> >     {
>> >         int key = 0;
>> >         int *val;
>> >
>> >         val = bpf_map_lookup_elem(&hmap, &key);
>> >         if (!val)
>> >             return TC_ACT_OK;
>> >         return TC_ACT_OK;
>> >     }
>> >
>> >     char __license[] SEC("license") = "GPL";
>> >
>> > Then I tried to use tc to load the program:
>> >     
>> >     tc qdisc add dev eth0 clsact
>> >     tc filter add dev eth0 egress bpf da obj test_bpf.o
>> >
>> > But the program loading failed with error messages:
>> >     Prog section 'classifier' rejected: Permission denied (13)!
>> >     - Type:          3
>> >     - Instructions:  9 (0 over limit
>> >     - License:       GPL
>> >
>> >     Verifier analysis:
>> >
>> >     Error fetching program/map!
>> >     Unable to load program
>> >
>> > I tried to replace the map definition with the following code and the program is loaded successfully!
>> >
>> >     struct bpf_map_def SEC("maps") hmap = {
>> >         .type = BPF_MAP_TYPE_HASH,
>> >         .key_size = sizeof(int),
>> >         .value_size = sizeof(int),
>> >         .max_entries = 1,
>> >     };
>> >
>> > With bpftrace, I can find that the errno -EACCES is returned by function do_check(). But I am still confused what's wrong with it.
>> >
>> > Linux Version: 5.17.0-rc3+ with CONFIG_DEBUG_INFO_BTF=y
>> > TC Version: 5.14.0
>> >
>> > Any suggestion will be appreciated!
>> 
>> If the latter works but the former doesn't, my guess would be that
>> iproute2 is compiled without libbpf support (in which case it would not
>> support BTF-defined maps either). If it does have libbpf support, that
>> (and the version of libbpf used) will be included in the output of `tc
>> -v`.
>> 
>> You could recompile iproute2 with enable libbpf support enabled, or as
>> Andrii suggests you can write your own loader using libbpf...
>> 
>
> It works with recompiled-iproute2. Thanks very much!

Great! You're welcome! :)

-Toke