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

[wuzongyo@mail.ustc.edu.cn]

> 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!

> -Toke


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