On Tue, 21 Sep 2021 18:06:35 +0200 Toke Høiland-Jørgensen wrote: > 1. Do nothing. This would make it up to users / sysadmins to avoid > anything breaking by manually making sure to not enable multi-buffer > support while loading any XDP programs that will malfunction if > presented with an mb frame. This will probably break in interesting > ways, but it's nice and simple from an implementation PoV. With this > we don't need the declaration discussed above either. > > 2. Add a check at runtime and drop the frames if they are mb-enabled and > the program doesn't understand it. This is relatively simple to > implement, but it also makes for difficult-to-understand issues (why > are my packets suddenly being dropped?), and it will incur runtime > overhead. > > 3. Reject loading of programs that are not MB-aware when running in an > MB-enabled mode. This would make things break in more obvious ways, > and still allow a userspace loader to declare a program "MB-aware" to > force it to run if necessary. The problem then becomes at what level > to block this? > > Doing this at the driver level is not enough: while a particular > driver knows if it's running in multi-buff mode, we can't know for > sure if a particular XDP program is multi-buff aware at attach time: > it could be tail-calling other programs, or redirecting packets to > another interface where it will be processed by a non-MB aware > program. > > So another option is to make it a global toggle: e.g., create a new > sysctl to enable multi-buffer. If this is set, reject loading any XDP > program that doesn't support multi-buffer mode, and if it's unset, > disable multi-buffer mode in all drivers. This will make it explicit > when the multi-buffer mode is used, and prevent any accidental subtle > malfunction of existing XDP programs. The drawback is that it's a > mode switch, so more configuration complexity. 4. Add new program type, XDP_MB. Do not allow mixing of XDP vs XDP_MB thru tail calls. IMHO that's very simple and covers majority of use cases.
