samples, bpf: Refactor pointer error check with libbpf

Current method of checking pointer error is not user friendly.
Especially the __must_check define makes this less intuitive.

Since, libbpf has an API libbpf_get_error() which checks pointer error,
this commit refactors existing pointer error check logic with libbpf.
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200516040608.1377876-2-danieltimlee@gmail.com

samples/bpf/sampleip_user.c

@@ -18,9 +18,6 @@
 #include "perf-sys.h"
 #include "trace_helpers.h"
 
-#define __must_check
-#include <linux/err.h>
-
 #define DEFAULT_FREQ	99
 #define DEFAULT_SECS	5
 #define MAX_IPS		8192
@@ -57,7 +54,7 @@ static int sampling_start(int freq, struct bpf_program *prog,
 			return 1;
 		}
 		links[i] = bpf_program__attach_perf_event(prog, pmu_fd);
-		if (IS_ERR(links[i])) {
+		if (libbpf_get_error(links[i])) {
 			fprintf(stderr, "ERROR: Attach perf event\n");
 			links[i] = NULL;
 			close(pmu_fd);
@@ -182,7 +179,7 @@ int main(int argc, char **argv)
 
 	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
 	obj = bpf_object__open_file(filename, NULL);
-	if (IS_ERR(obj)) {
+	if (libbpf_get_error(obj)) {
 		fprintf(stderr, "ERROR: opening BPF object file failed\n");
 		obj = NULL;
 		goto cleanup;

samples/bpf/trace_event_user.c

@@ -16,9 +16,6 @@
 #include "perf-sys.h"
 #include "trace_helpers.h"
 
-#define __must_check
-#include <linux/err.h>
-
 #define SAMPLE_FREQ 50
 
 static int pid;
@@ -159,7 +156,7 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
 			goto all_cpu_err;
 		}
 		links[i] = bpf_program__attach_perf_event(prog, pmu_fd);
-		if (IS_ERR(links[i])) {
+		if (libbpf_get_error(links[i])) {
 			printf("bpf_program__attach_perf_event failed\n");
 			links[i] = NULL;
 			close(pmu_fd);
@@ -198,7 +195,7 @@ static void test_perf_event_task(struct perf_event_attr *attr)
 		goto err;
 	}
 	link = bpf_program__attach_perf_event(prog, pmu_fd);
-	if (IS_ERR(link)) {
+	if (libbpf_get_error(link)) {
 		printf("bpf_program__attach_perf_event failed\n");
 		link = NULL;
 		close(pmu_fd);
@@ -314,7 +311,7 @@ int main(int argc, char **argv)
 	}
 
 	obj = bpf_object__open_file(filename, NULL);
-	if (IS_ERR(obj)) {
+	if (libbpf_get_error(obj)) {
 		printf("opening BPF object file failed\n");
 		obj = NULL;
 		goto cleanup;

samples/bpf/xdp_redirect_cpu_user.c

@@ -19,9 +19,6 @@ static const char *__doc__ =
 #include <time.h>
 #include <linux/limits.h>
 
-#define __must_check
-#include <linux/err.h>
-
 #include <arpa/inet.h>
 #include <linux/if_link.h>
 
@@ -622,7 +619,7 @@ static struct bpf_link * attach_tp(struct bpf_object *obj,
 	}
 
 	link = bpf_program__attach_tracepoint(prog, tp_category, tp_name);
-	if (IS_ERR(link))
+	if (libbpf_get_error(link))
 		exit(EXIT_FAIL_BPF);
 
 	return link;