[PATCH bpf-next v3 3/6] libbpf: Propagate EPERM to caller on program load

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

From: Toke Høiland-Jørgensen <toke@redhat.com>

When loading an eBPF program, libbpf overrides the return code for EPERM
errors instead of returning it to the caller. This makes it hard to figure
out what went wrong on load.

In particular, EPERM is returned when the system rlimit is too low to lock
the memory required for the BPF program. Previously, this was somewhat
obscured because the rlimit error would be hit on map creation (which does
return it correctly). However, since maps can now be reused, object load
can proceed all the way to loading programs without hitting the error;
propagating it even in this case makes it possible for the caller to react
appropriately (and, e.g., attempt to raise the rlimit before retrying).

Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/libbpf.c |   27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a70ade546a73..094f5c64611a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3721,7 +3721,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 		free(log_buf);
 		goto retry_load;
 	}
-	ret = -LIBBPF_ERRNO__LOAD;
+	ret = -errno;
 	cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
 	pr_warn("load bpf program failed: %s\n", cp);
 
@@ -3734,23 +3734,18 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 		pr_warn("Program too large (%zu insns), at most %d insns\n",
 			load_attr.insns_cnt, BPF_MAXINSNS);
 		ret = -LIBBPF_ERRNO__PROG2BIG;
-	} else {
+	} else if (load_attr.prog_type != BPF_PROG_TYPE_KPROBE) {
 		/* Wrong program type? */
-		if (load_attr.prog_type != BPF_PROG_TYPE_KPROBE) {
-			int fd;
-
-			load_attr.prog_type = BPF_PROG_TYPE_KPROBE;
-			load_attr.expected_attach_type = 0;
-			fd = bpf_load_program_xattr(&load_attr, NULL, 0);
-			if (fd >= 0) {
-				close(fd);
-				ret = -LIBBPF_ERRNO__PROGTYPE;
-				goto out;
-			}
-		}
+		int fd;
 
-		if (log_buf)
-			ret = -LIBBPF_ERRNO__KVER;
+		load_attr.prog_type = BPF_PROG_TYPE_KPROBE;
+		load_attr.expected_attach_type = 0;
+		fd = bpf_load_program_xattr(&load_attr, NULL, 0);
+		if (fd >= 0) {
+			close(fd);
+			ret = -LIBBPF_ERRNO__PROGTYPE;
+			goto out;
+		}
 	}
 
 out: