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From:   Magnus Karlsson <magnus.karlsson@gmail.com>
Date:   Wed, 2 Jun 2021 10:53:54 +0200
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Subject: Re: [PATCH net-next] xsk: Return -EINVAL instead of -EBUSY after
 xsk_get_pool_from_qid() fails
To:     =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= <toke@redhat.com>
Cc:     Wang Hai <wanghai38@huawei.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@intel.com>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Wed, Jun 2, 2021 at 10:38 AM Toke H=C3=B8iland-J=C3=B8rgensen <toke@redh=
at.com> wrote:
>
> Magnus Karlsson <magnus.karlsson@gmail.com> writes:
>
> > On Wed, Jun 2, 2021 at 6:02 AM Wang Hai <wanghai38@huawei.com> wrote:
> >>
> >> xsk_get_pool_from_qid() fails not because the device's queues are busy=
,
> >> but because the queue_id exceeds the current number of queues.
> >> So when it fails, it is better to return -EINVAL instead of -EBUSY.
> >>
> >> Signed-off-by: Wang Hai <wanghai38@huawei.com>
> >> ---
> >>  net/xdp/xsk_buff_pool.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> >> index 8de01aaac4a0..30ece117117a 100644
> >> --- a/net/xdp/xsk_buff_pool.c
> >> +++ b/net/xdp/xsk_buff_pool.c
> >> @@ -135,7 +135,7 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
> >>                 return -EINVAL;
> >>
> >>         if (xsk_get_pool_from_qid(netdev, queue_id))
> >> -               return -EBUSY;
> >> +               return -EINVAL;
> >
> > I guess your intent here is to return -EINVAL only when the queue_id
> > is larger than the number of active queues. But this patch also
> > changes the return code when the queue id is already in use and in
> > that case we should continue to return -EBUSY. As this function is
> > used by a number of drivers, the easiest way to accomplish this is to
> > introduce a test for queue_id out of bounds before this if-statement
> > and return -EINVAL there.
>
> Isn't the return code ABI by now, though?

You are probably right and in that case this should not change at all.
It has been returning this for quite a while too as it is nothing new.
But I leave the final decision to other people on the list.

> -Toke
>