linux-kernel - Re: [PATCH bpf] samples/bpf: Fix the error return code of xdp

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Message-ID: <6f35ad34-1334-bdae-da7f-a20f1af34ea5@huawei.com>
Date:   Mon, 5 Jul 2021 15:45:07 +0800
From:   "wanghai (M)" <wanghai38@...wei.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
        <hawk@...nel.org>, <john.fastabend@...il.com>, <andrii@...nel.org>,
        <kafai@...com>, <songliubraving@...com>, <yhs@...com>,
        <kpsingh@...nel.org>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] samples/bpf: Fix the error return code of
 xdp_redirect's main()


在 2021/7/2 18:29, Jesper Dangaard Brouer 写道:
>
> On 16/06/2021 06.25, Wang Hai wrote:
>> Fix to return a negative error code from the error handling
>> case instead of 0, as done elsewhere in this function.
>
> The main() function in C should never return a negative value on Unix 
> POSIX systems.
>
>
> There is a good explaination in exit(3p): `man 3p exit`
>
>    The  value  of  status may be 0, EXIT_SUCCESS, EXIT_FAILURE, or any 
> other value, though only the least significant 8 bits (that is, status 
> & 0377) shall be available to a waiting parent process.
>
> Thus, negative values are often seen as 255 in the $? program exit 
> status variable $?.
>
>
> Also explained in exit(3):
>
>     The C standard specifies two constants, EXIT_SUCCESS=0 and 
> EXIT_FAILURE=1.
>
> I see the 'samples/bpf/xdp_redirect_user.c' in most places just use 0 
> or 1.
>
Got it, thanks for the explanation, I will fix it to return 1, just like 
the other error paths in samples/bpf/xdp_redirect_user.c
>
>> If bpf_map_update_elem() failed, main() should return a negative error.
>>
>> Fixes: 832622e6bd18 ("xdp: sample program for new bpf_redirect helper")
>> Signed-off-by: Wang Hai <wanghai38@...wei.com>
>> ---
>>   samples/bpf/xdp_redirect_user.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/samples/bpf/xdp_redirect_user.c 
>> b/samples/bpf/xdp_redirect_user.c
>> index 41d705c3a1f7..c903f1ccc15e 100644
>> --- a/samples/bpf/xdp_redirect_user.c
>> +++ b/samples/bpf/xdp_redirect_user.c
>> @@ -213,5 +213,5 @@ int main(int argc, char **argv)
>>       poll_stats(2, ifindex_out);
>>     out:
>> -    return 0;
>> +    return ret;
>>   }
>
>
> (Sorry, I didn't complain it time as I see this patch is already applied)
>
> .
>