> On Oct 2, 2019, at 11:38 AM, Song Liu <songliubraving@xxxxxx> wrote: > > > >> On Oct 2, 2019, at 6:30 AM, Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> >> This series adds support for executing multiple XDP programs on a single >> interface in sequence, through the use of chain calls, as discussed at the Linux >> Plumbers Conference last month: >> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__linuxplumbersconf.org_event_4_contributions_460_&d=DwIDaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=dR8692q0_uaizy0jkrBJQM5k2hfm4CiFxYT8KaysFrg&m=YXqqHTC51zXBviPBEk55y-fQjFQwcXWFlH0IoOqm2KU&s=NF4w3eSPmNhSpJr1-0FLqqlqfgEV8gsCQb9YqWQ9p-k&e= >> >> # HIGH-LEVEL IDEA >> >> The basic idea is to express the chain call sequence through a special map type, >> which contains a mapping from a (program, return code) tuple to another program >> to run in next in the sequence. Userspace can populate this map to express >> arbitrary call sequences, and update the sequence by updating or replacing the >> map. >> >> The actual execution of the program sequence is done in bpf_prog_run_xdp(), >> which will lookup the chain sequence map, and if found, will loop through calls >> to BPF_PROG_RUN, looking up the next XDP program in the sequence based on the >> previous program ID and return code. >> >> An XDP chain call map can be installed on an interface by means of a new netlink >> attribute containing an fd pointing to a chain call map. This can be supplied >> along with the XDP prog fd, so that a chain map is always installed together >> with an XDP program. > > Interesting work! > > Quick question: can we achieve the same by adding a "retval to call_tail_next" > map to each program? I think one issue is how to avoid loop like A->B->C->A, > but this should be solvable? Also, could you please share a real word example? I saw the example from LPC slides, but I am more curious about what does each program do in real use cases. Thanks, Song
