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SubjectRe: Exporting obscene amounts of data in rtnl_link_ops->fill_info()
On Wed, Aug 19, 2015 at 5:47 PM, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Hi guys,
>
> I have a new link driver that registers a rtnl_link_ops. For many
> things, the rtnl interfaces are perfectly suited: I can use netlink in
> userspace to check out packet counts, adjust interface parameters, and
> all sorts of things. There is even the "fill_info" function exporting
> interface-specific types of data to userspace through the standard
> netlink interfaces. I'm glad this is here, because it's exactly what I
> want.
>
> Problem: sometimes I want to export a *lot* of data to userspace. When
> this happens, even if I make the netlink socket receive buffer really
> huge, this code path is still reached in rtnetlink.c:
>
> err = rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
> NETLINK_CB(cb->skb).portid,
> cb->nlh->nlmsg_seq, 0,
> NLM_F_MULTI,
> ext_filter_mask);
> /* If we ran out of room on the first message,
> * we're in trouble
> */
> WARN_ON((err == -EMSGSIZE) && (skb->len == 0));
>
> That is -- it tries to fill the skb (for sending it back to
> userspace), but doesn't have enough room, so it returns -EMSGSIZE.
> That seems like reasonable behavior, but it doesn't really help me
> obtain my goal. I'd like to send quite a bit of data back to userspace
> for a network interface, and I'd like to do it using the standard
> netlink APIs. Is this possible?



What kind of data are you sending up? Maybe there is an alternate interface.


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