Re: [PATCH bpf-next v3 2/3] libbpf: add low level TC-BPF API

On 4/22/21 1:08 AM, Kumar Kartikeya Dwivedi wrote:

On Thu, Apr 22, 2021 at 04:29:28AM IST, Daniel Borkmann wrote:

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On 4/20/21 9:37 PM, Kumar Kartikeya Dwivedi wrote:
[...]

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diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index bec4e6a6e31d..b4ed6a41ea70 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h

@@ -16,6 +16,8 @@
   #include <stdbool.h>
   #include <sys/types.h>  // for size_t
   #include <linux/bpf.h>
+#include <linux/pkt_sched.h>
+#include <linux/tc_act/tc_bpf.h>
   #include "libbpf_common.h"

@@ -775,6 +777,48 @@ LIBBPF_API int bpf_linker__add_file(struct bpf_linker *linker, const char *filen
   LIBBPF_API int bpf_linker__finalize(struct bpf_linker *linker);
   LIBBPF_API void bpf_linker__free(struct bpf_linker *linker);
+/* Convenience macros for the clsact attach hooks */
+#define BPF_TC_CLSACT_INGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_INGRESS)
+#define BPF_TC_CLSACT_EGRESS TC_H_MAKE(TC_H_CLSACT, TC_H_MIN_EGRESS)

I would abstract those away into an enum, plus avoid having to pull in
linux/pkt_sched.h and linux/tc_act/tc_bpf.h from main libbpf.h header.

Just add a enum { BPF_TC_DIR_INGRESS, BPF_TC_DIR_EGRESS, } and then the
concrete tc bits (TC_H_MAKE()) can be translated internally.

Ok, will do.

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+struct bpf_tc_opts {
+	size_t sz;

Is this set anywhere?

This is needed by the OPTS_* infrastructure.

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+	__u32 handle;
+	__u32 class_id;

I'd remove class_id from here as well given in direct-action a BPF prog can
set it if needed.

Ok, makes sense.

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+	__u16 priority;
+	bool replace;
+	size_t :0;

What's the rationale for this padding?

dde7b3f5f2f4 ("libbpf: Add explicit padding to bpf_xdp_set_link_opts")

Hm, fair enough.

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+};
+
+#define bpf_tc_opts__last_field replace
+
+/* Acts as a handle for an attached filter */
+struct bpf_tc_attach_id {

nit: maybe bpf_tc_ctx

Noted.

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+	__u32 handle;
+	__u16 priority;
+};
+
+struct bpf_tc_info {
+	struct bpf_tc_attach_id id;
+	__u16 protocol;
+	__u32 chain_index;
+	__u32 prog_id;
+	__u8 tag[BPF_TAG_SIZE];
+	__u32 class_id;
+	__u32 bpf_flags;
+	__u32 bpf_flags_gen;

Given we do not yet have any setters e.g. for offload, etc, the one thing
I'd see useful and crucial initially is prog_id.

The protocol, chain_index, and I would also include tag should be dropped.

A future user of this API needs to know the tag, so I would like to keep that.
The rest we can drop, and probably document the default values explicitly.

Couldn't this be added along with the future patch for the [future] user?

The tag should be the tag of the prog itself, so if you have prog_id, you
could also retrieve the same tag from the prog. The tag was basically from
the early days where we didn't have bpf_prog_get_info_by_fd().

What does that future user need to do different here?

Thanks,
Daniel