Jakub Kicinski <kuba@xxxxxxxxxx> writes: > On Thu, 19 Mar 2020 14:13:13 +0100 Toke Høiland-Jørgensen wrote: >> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> >> >> 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@xxxxxxxxxx> > > I didn't know we wanted to go ahead with this... Well, I'm aware of the bpf_link discussion, obviously. Not sure what's happening with that, though. So since this is a straight-forward extension of the existing API, that doesn't carry a high implementation cost, I figured I'd just go ahead with this. Doesn't mean we can't have something similar in bpf_link as well, of course. > If we do please run this thru checkpatch, set .strict_start_type, Will do. > and make the expected fd unsigned. A negative expected fd makes no > sense. A negative expected_fd corresponds to setting the UPDATE_IF_NOEXIST flag. I guess you could argue that since we have that flag, setting a negative expected_fd is not strictly needed. However, I thought it was weird to have a "this is what I expect" API that did not support expressing "I expect no program to be attached". -Toke
