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

On Thu, 19 Mar 2020 14:13:13 +0100 Toke Høiland-Jørgensen wrote:

From: Toke Høiland-Jørgensen <redacted>

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 <redacted>

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.