bpf: make error reporting in bpf_warn_invalid_xdp_action more clear

Differ between illegal XDP action code and just driver unsupported one to provide better feedback when we throw a one-time warning here. Reason is that with 814abfabef3c ("xdp: add bpf_redirect helper function") not all drivers support the new XDP return code yet and thus they will fall into their 'default' case when checking for return codes after program return, which then triggers a bpf_warn_invalid_xdp_action() stating that the return code is illegal, but from XDP perspective it's not. I decided not to place something like a XDP_ACT_MAX define into uapi i) given we don't have this either for all other program types, ii) future action codes could have further encoding there, which would render such define unsuitable and we wouldn't be able to rip it out again, and iii) we rarely add new action codes.

Daniel Borkmann committed 9 years ago

Commit 9beb8be1 parent a010a2f2 files · +7 −3Browse files

Showing the changes to include/uapi/linux (1 of 2 files). Show all

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include/uapi/linux/bpf.h+2−2

@@ -766,8 +766,8 @@ struct bpf_sock { · 765 unmodified lines
766	766
767	767	/* User return codes for XDP prog type.
768	768	* A valid XDP program must return one of these defined values. All other
769		− * return codes are reserved for future use. Unknown return codes will result
770		− * in packet drop.
	769	+ * return codes are reserved for future use. Unknown return codes will
	770	+ * result in packet drops and a warning via bpf_warn_invalid_xdp_action().
771	771	*/
772	772	enum xdp_action {
773	773	XDP_ABORTED = 0,