[PATCH bpf-next 1/2] libbpf: Move XDP frags flag to prog_flags

["Toke Høiland-Jørgensen" <toke@redhat.com>]

The libbpf section definition for XDP frags support stores the flags bit
in the private section definition cookie from object open to load time.
This has the unfortunate consequence that API consumers cannot see (or
manipulate) the flag between object open and program load.

In particular, libxdp has special handling of frags-enabled programs to
make them compatible with the dispatcher. This doesn't work on XDP
programs that enable frags through the 'xdp.frags' section definition
because the flag is not visible through bpf_program__flags()[0].

Fix this by changing how libbpf loads the 'xdp.frags' section: instead
of using the private section definition cookie, add a setup function to
the section definition that stores the flag in the prog_flags field of
struct bpf_program.

[0] https://github.com/xdp-project/xdp-tools/issues/587

Fixes: 082c4bfba4f7 ("libbpf: Add SEC name for xdp frags programs")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/libbpf.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b749c01742ee..7d6f0fe518d9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -420,10 +420,8 @@ enum sec_def_flags {
 	SEC_ATTACH_BTF = 4,
 	/* BPF program type allows sleeping/blocking in kernel */
 	SEC_SLEEPABLE = 8,
-	/* BPF program support non-linear XDP buffer */
-	SEC_XDP_FRAGS = 16,
 	/* Setup proper attach type for usdt probes. */
-	SEC_USDT = 32,
+	SEC_USDT = 16,
 };
 
 struct bpf_sec_def {
@@ -7879,6 +7877,12 @@ static int tracing_multi_mod_fd(struct bpf_program *prog, int *btf_obj_fd)
 	return 0;
 }
 
+static int setup_xdp_frags(struct bpf_program *prog, long cookie)
+{
+	prog->prog_flags |= BPF_F_XDP_HAS_FRAGS;
+	return 0;
+}
+
 /* this is called as prog->sec_def->prog_prepare_load_fn for libbpf-supported sec_defs */
 static int libbpf_prepare_prog_load(struct bpf_program *prog,
 				    struct bpf_prog_load_opts *opts, long cookie)
@@ -7892,9 +7896,6 @@ static int libbpf_prepare_prog_load(struct bpf_program *prog,
 	if (def & SEC_SLEEPABLE)
 		opts->prog_flags |= BPF_F_SLEEPABLE;
 
-	if (prog->type == BPF_PROG_TYPE_XDP && (def & SEC_XDP_FRAGS))
-		opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;
-
 	/* special check for usdt to use uprobe_multi link */
 	if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK)) {
 		/* for BPF_TRACE_UPROBE_MULTI, user might want to query expected_attach_type
@@ -10182,11 +10183,11 @@ static const struct bpf_sec_def section_defs[] = {
 	SEC_DEF("iter+",		TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF, attach_iter),
 	SEC_DEF("iter.s+",		TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_iter),
 	SEC_DEF("syscall",		SYSCALL, 0, SEC_SLEEPABLE),
-	SEC_DEF("xdp.frags/devmap",	XDP, BPF_XDP_DEVMAP, SEC_XDP_FRAGS),
+	SEC_DEF("xdp.frags/devmap",	XDP, BPF_XDP_DEVMAP, SEC_NONE, .prog_setup_fn = setup_xdp_frags),
 	SEC_DEF("xdp/devmap",		XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE),
-	SEC_DEF("xdp.frags/cpumap",	XDP, BPF_XDP_CPUMAP, SEC_XDP_FRAGS),
+	SEC_DEF("xdp.frags/cpumap",	XDP, BPF_XDP_CPUMAP, SEC_NONE, .prog_setup_fn = setup_xdp_frags),
 	SEC_DEF("xdp/cpumap",		XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE),
-	SEC_DEF("xdp.frags",		XDP, BPF_XDP, SEC_XDP_FRAGS),
+	SEC_DEF("xdp.frags",		XDP, BPF_XDP, SEC_NONE, .prog_setup_fn = setup_xdp_frags),
 	SEC_DEF("xdp",			XDP, BPF_XDP, SEC_ATTACHABLE_OPT),
 	SEC_DEF("perf_event",		PERF_EVENT, 0, SEC_NONE),
 	SEC_DEF("lwt_in",		LWT_IN, 0, SEC_NONE),
-- 
2.55.0