Re: [PATCH bpf-next 1/4] xdp: Support specifying expected existing program when attaching XDP

Jakub Kicinski
2020-03-19T22:52:40Z

On Thu, 19 Mar 2020 14:13:13 +0100 Toke Høiland-Jørgensen wrote:
> From: Toke Høiland-Jørgensen <toke@redhat.com>
>
> While it is currently possible for userspace to specify that an existing
> XDP program should not be replaced when attaching to an interface, there is
> no mechanism to safely replace a specific XDP program with another.
>
> This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be
> set along with IFLA_XDP_FD. If set, the kernel will check that the program
> currently loaded on the interface matches the expected one, and fail the
> operation if it does not. This corresponds to a 'cmpxchg' memory operation.
>
> A new companion flag, XDP_FLAGS_EXPECT_FD, is also added to explicitly
> request checking of the EXPECTED_FD attribute. This is needed for userspace
> to discover whether the kernel supports the new attribute.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>

I didn't know we wanted to go ahead with this...

If we do please run this thru checkpatch, set .strict_start_type, and
make the expected fd unsigned. A negative expected fd makes no sense.