On 25/3/26 00:18, Toke Høiland-Jørgensen wrote:

Leon Hwang [off-list ref] writes:

quoted

xdp_has_frags was introduced by the commit
c2f2cdbeffda ("bpf: introduce BPF_F_XDP_HAS_FRAGS flag in prog_flags loading the ebpf program").

The commit f45d5b6ce2e8 ("bpf: generalise tail call map compatibility check")
was to ensure backwards compatibility against tail calls. However, it
missed that XDP progs can be extended by freplace progs, which could break
the backwards compatibility, e.g. xdp_has_frags=true freplace progs are
allowed to attach to xdp_has_frags=false XDP progs.

To avoid breaking the backwards compatibility via freplace, disallow
freplace on XDP programs with different xdp_has_frags values.

The problem you describe is not actually a problem, though? A
frags-aware program can run on a non-frags interface just fine.

You're messing with long-standing behaviour (since 5.18!) to solve a
non-existent problem. In a way that completely breaks the frags handling
in libxdp[0]:

    Running tests from ./test-libxdp.sh
     [test_link_so]                PASS
     [test_link_a]                 PASS
     [test_old_dispatcher]         PASS
     [test_xdp_devbound]           PASS
     [test_xdp_frags]              FAIL
          Kernel supports XDP programs with frags
          check_load_frags:	FAILED
          check_load_nofrags_success:	PASSED
          check_load_nofrags_fail:	PASSED
          check_load_frags_multi:	FAILED
          check_load_mix_big:	FAILED
          check_load_mix_small:	FAILED
          Test test_xdp_frags exited with return code: 1


Please don't do that.

-Toke

[0] Run 'make test' here: https://github.com/xdp-project/xdp-tools

Indeed, it failed to 'make test'.

Will drop this patch in v2, as it wasn't an issue.

Thanks,
Leon