bpftool: Fix error message of strerror

strerror() expects a positive errno, however variable err will never be
positive when an error occurs. This causes bpftool to output too many
"unknown error", even a simple "file not exist" error can not get an
accurate message.

This patch fixed all "strerror(err)" patterns in bpftool.
Specially in btf.c#L823, hashmap__append() is an internal function of
libbpf and will not change errno, so there's a little difference.
Some libbpf_get_error() calls are kept for return values.

Changes since v1: https://lore.kernel.org/bpf/SY4P282MB1084B61CD8671DFA395AA8579D539@SY4P282MB1084.AUSP282.PROD.OUTLOOK.COM/
Check directly for NULL values instead of calling libbpf_get_error().

Signed-off-by: Tianyi Liu <i.pear@outlook.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/SY4P282MB1084AD9CD84A920F08DF83E29D549@SY4P282MB1084.AUSP282.PROD.OUTLOOK.COM

1 files changed, 3 insertions, 4 deletions

diff --git a/tools/bpf/bpftool/map_perf_ring.c b/tools/bpf/bpftool/map_perf_ring.c
index 1583281d1327..21d7d447e1f3 100644
--- a/tools/bpf/bpftool/map_perf_ring.c
+++ b/tools/bpf/bpftool/map_perf_ring.c
@@ -188,10 +188,9 @@ int do_event_pipe(int argc, char **argv)
 	opts.map_keys = &ctx.idx;
 	pb = perf_buffer__new_raw(map_fd, MMAP_PAGE_CNT, &perf_attr,
 				  print_bpf_output, &ctx, &opts);
-	err = libbpf_get_error(pb);
-	if (err) {
+	if (!pb) {
 		p_err("failed to create perf buffer: %s (%d)",
-		      strerror(err), err);
+		      strerror(errno), errno);
 		goto err_close_map;
 	}
 
@@ -206,7 +205,7 @@ int do_event_pipe(int argc, char **argv)
 		err = perf_buffer__poll(pb, 200);
 		if (err < 0 && err != -EINTR) {
 			p_err("perf buffer polling failed: %s (%d)",
-			      strerror(err), err);
+			      strerror(errno), errno);
 			goto err_close_pb;
 		}
 	}