On Fri, Sep 5, 2025 at 8:22 AM Stanislav Fomichev <stfomic...@gmail.com> wrote:
>
> On 09/04, Mina Almasry wrote:
> > On Thu, Sep 4, 2025 at 11:27 AM Stanislav Fomichev <s...@fomichev.me> wrote:
> > >
> > > devmem test fails on NIPA. Most likely we get skb(s) with readable
> > > frags (why?)
> >
> > I would expect if we get readable frags that the frags land in the
> > host buffer we provide ncdevmem and we actually hit this error:
> >
> > ```
> > 1 if (!is_devmem) {
> > 0 pr_err("flow steering error");
> > 1 goto err_close_client;
> > 2 }
> > ```
> >
> > which as it says, should be root caused in a flow steering error. I
> > don't know what would cause an EFAULT off the top of my head.
>
> Yea, I don't understand what happens :-( I'm thinking of doing the
> following as well:
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 40b774b4f587..0c18a8c7965f 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2820,7 +2820,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct
> msghdr *msg, size_t len,
> used);
> if (err <= 0) {
> if (!copied)
> - copied = -EFAULT;
> + copied = err;
>
> break;
> }
>
> Should give us more info for the devmem case... LMK if you don't like
> it. If I don't hear from you in a couple of days, I'll send it out..
Hmm, the other code paths overwrite the error to EFAULT; I don't know
if that's significant in some way. But seems fine to me, I don't see
why not do this, other than maybe potentional confusion with recvmsg
returning an error not documented here:
https://linux.die.net/man/2/recvmsg
But that seems a minor point.
--
Thanks,
Mina
