netdev - Re: [PATCH] libbpf: Don't error out if getsockopt() fails for XDP

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Date:   Fri, 13 Sep 2019 18:53:20 +0000
From:   Yonghong Song <yhs@...com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "maximmi@...lanox.com" <maximmi@...lanox.com>
Subject: Re: [PATCH] libbpf: Don't error out if getsockopt() fails for
 XDP_OPTIONS



On 9/10/19 12:06 AM, Toke Høiland-Jørgensen wrote:
> Yonghong Song <yhs@...com> writes:
> 
>> On 9/9/19 10:46 AM, Toke Høiland-Jørgensen wrote:
>>> The xsk_socket__create() function fails and returns an error if it cannot
>>> get the XDP_OPTIONS through getsockopt(). However, support for XDP_OPTIONS
>>> was not added until kernel 5.3, so this means that creating XSK sockets
>>> always fails on older kernels.
>>>
>>> Since the option is just used to set the zero-copy flag in the xsk struct,
>>> there really is no need to error out if the getsockopt() call fails.
>>>
>>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>>> ---
>>>    tools/lib/bpf/xsk.c | 8 ++------
>>>    1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
>>> index 680e63066cf3..598e487d9ce8 100644
>>> --- a/tools/lib/bpf/xsk.c
>>> +++ b/tools/lib/bpf/xsk.c
>>> @@ -603,12 +603,8 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>>>    
>>>    	optlen = sizeof(opts);
>>>    	err = getsockopt(xsk->fd, SOL_XDP, XDP_OPTIONS, &opts, &optlen);
>>> -	if (err) {
>>> -		err = -errno;
>>> -		goto out_mmap_tx;
>>> -	}
>>> -
>>> -	xsk->zc = opts.flags & XDP_OPTIONS_ZEROCOPY;
>>> +	if (!err)
>>> +		xsk->zc = opts.flags & XDP_OPTIONS_ZEROCOPY;
>>>    
>>>    	if (!(xsk->config.libbpf_flags & XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD)) {
>>>    		err = xsk_setup_xdp_prog(xsk);
>>
>> Since 'zc' is not used by anybody, maybe all codes 'zc' related can be
>> removed? It can be added back back once there is an interface to use
>> 'zc'?
> 
> Fine with me; up to the maintainers what they prefer, I guess? :)

Maxim,

Your originally introduced `'zc' and getting XDP_OPTIONS.
What is your opinion of how to deal with the unused xsk->zc?

> 
> -Toke
>