On Fri, Feb 28, 2020 at 6:22 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Hi everyone > > As most of you are no doubt aware, we've had various discussions on how > to handle multiple XDP programs on a single interface. With the freplace > functionality, the kernel infrastructure is now there to handle this > (almost, see "missing pieces" below). > > While the freplace mechanism offers userspace a lot of flexibility in > how to handle dispatching of multiple XDP programs, userspace also has > to do quite a bit of work to implement this (compared to just issuing > load+attach). The goal of this email is to get some feedback on a > library to implement this, in the hope that we can converge on something > that will be widely applicable, ensuring that both (a) everyone doesn't > have to reinvent the wheel, and (b) we don't end up with a proliferation > of subtly incompatible dispatcher models that makes it hard or > impossible to mix and match XDP programs from multiple sources. > [...] > > **** Missing pieces > While the libxdp code can assemble a basic dispatcher and load it into the > kernel, there are a couple of missing pieces on the kernel side; I will propose > patches to fix these, but figured there was no reason to hold back posting of > the library for comments because of this. These missing pieces are: > > - There is currently no way to persist the freplace after the program exits; the > file descriptor returned by bpf_raw_tracepoint_open() will release the program > when it is closed, and it cannot be pinned. This is completely addressed by patch set [0] I just posted. It will allow you to pin freplace BPF link in BPF FS. Feel free to review and comment there, if anything is missing. [0] https://patchwork.ozlabs.org/project/netdev/list/?series=161582&state=* > > - There is no way to re-attach an already loaded program to another function; > this is needed for updating the call sequence: When a new program is loaded, > libxdp should get the existing list of component programs on the interface and > insert the new one into the chain in the appropriate place. To do this it > needs to build a new dispatcher and reattach all the old programs to it. > Ideally, this should be doable without detaching them from the old dispatcher; > that way, we can build the new dispatcher completely, and atomically replace > it on the interface by the usual XDP attach mechanism. > > --- > > Toke Høiland-Jørgensen (1): > libxdp: Add libxdp (FOR COMMENT ONLY) > > > tools/lib/xdp/libxdp.c | 856 +++++++++++++++++++++++++++++++++++++++ > tools/lib/xdp/libxdp.h | 38 ++ > tools/lib/xdp/prog_dispatcher.h | 17 + > tools/lib/xdp/xdp-dispatcher.c | 178 ++++++++ > tools/lib/xdp/xdp_helpers.h | 12 + > 5 files changed, 1101 insertions(+) > create mode 100644 tools/lib/xdp/libxdp.c > create mode 100644 tools/lib/xdp/libxdp.h > create mode 100644 tools/lib/xdp/prog_dispatcher.h > create mode 100644 tools/lib/xdp/xdp-dispatcher.c > create mode 100644 tools/lib/xdp/xdp_helpers.h >
