netdev - Re: [oss-drivers] Re: [PATCH bpf-next] bpf: add BTF ids in procfs for file descriptors to BTF objects

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Date:   Tue, 20 Aug 2019 14:48:30 +0100
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [oss-drivers] Re: [PATCH bpf-next] bpf: add BTF ids in procfs for
 file descriptors to BTF objects

2019-08-20 15:36 UTC+0200 ~ Daniel Borkmann <daniel@...earbox.net>
> On 8/20/19 11:52 AM, Quentin Monnet wrote:
>> Implement the show_fdinfo hook for BTF FDs file operations, and make it
>> print the id and the size of the BTF object. This allows for a quick
>> retrieval of the BTF id from its FD; or it can help understanding what
>> type of object (BTF) the file descriptor points to.
>>
>> Signed-off-by: Quentin Monnet <quentin.monnet@...ronome.com>
>> Reviewed-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
>> ---
>>   kernel/bpf/btf.c | 16 ++++++++++++++++
>>   1 file changed, 16 insertions(+)
>>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index 5fcc7a17eb5a..39e184f1b27c 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -3376,6 +3376,19 @@ void btf_type_seq_show(const struct btf *btf,
>> u32 type_id, void *obj,
>>       btf_type_ops(t)->seq_show(btf, t, type_id, obj, 0, m);
>>   }
>>   +#ifdef CONFIG_PROC_FS
>> +static void bpf_btf_show_fdinfo(struct seq_file *m, struct file *filp)
>> +{
>> +    const struct btf *btf = filp->private_data;
>> +
>> +    seq_printf(m,
>> +           "btf_id:\t%u\n"
>> +           "data_size:\t%u\n",
>> +           btf->id,
>> +           btf->data_size);
> 
> Looks good, exposing btf_id makes sense to me in order to correlate with
> applications.
> Do you have a concrete use case for data_size to expose it this way as
> opposed to fetch
> it via btf_get_info_by_fd()? If not, I'd say lets only add btf_id in there.

No, I don't have one for data_size to be honest. I'll respin with btf_id
only then.

Thanks,
Quentin