On 1/28/25 14:49, Willem de Bruijn wrote:

quoted

quoted

quoted

+struct net_devmem_dmabuf_binding *
+net_devmem_get_sockc_binding(struct sock *sk, struct sockcm_cookie *sockc)
+{
+     struct net_devmem_dmabuf_binding *binding;
+     int err = 0;
+
+     binding = net_devmem_lookup_dmabuf(sockc->dmabuf_id);

This lookup is from global xarray net_devmem_dmabuf_bindings.

Is there a check that the socket is sending out through the device
to which this dmabuf was bound with netlink? Should there be?
(e.g., SO_BINDTODEVICE).

Yes, I think it may be an issue if the user triggers a send from a
different netdevice, because indeed when we bind a dmabuf we bind it
to a specific netdevice.

One option is as you say to require TX sockets to be bound and to
check that we're bound to the correct netdev. I also wonder if I can
make this work without SO_BINDTODEVICE, by querying the netdev the
sock is currently trying to send out on and doing a check in the
tcp_sendmsg. I'm not sure if this is possible but I'll give it a look.

I was a bit quick on mentioning SO_BINDTODEVICE. Agreed that it is
vastly preferable to not require that, but infer the device from
the connected TCP sock.

I wonder why so? I'd imagine something like SO_BINDTODEVICE is a
better way to go. The user has to do it anyway, otherwise packets
might go to a different device and the user would suddenly start
getting errors with no good way to alleviate them (apart from
likes of SO_BINDTODEVICE). It's even worse if it works for a while
but starts to unpredictably fail as time passes. With binding at
least it'd fail fast if the setup is not done correctly.

-- 
Pavel Begunkov