libbpf-tools: filelife: Fix problem when using perf-buffer

When ring buffers are not supported, will fallback to perf-buffer. The
map type is set for the perf buffer in `bpf_buffer__new()`. This setting
must be done before the BPF program is loaded. Otherwise,
`BPF_MAP_TYPE_RINGBUF` will be used in `bpf_perf_event_output()`,
resulting in the following error message:

    ; return bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, buf, size); @ compat.bpf.h:46
    136: (79) r1 = *(u64 *)(r10 -40)      ; R1_w=ctx() R10=fp0 fp-40=ctx()
    137: (18) r2 = 0xffff8bd101623c00     ; R2_w=map_ptr(map=events,ks=0,vs=0)
    139: (18) r3 = 0xffffffff             ; R3_w=0xffffffff
    141: (bf) r4 = r7                     ; R4_w=map_value(map=heap,ks=4,vs=10240) R7=map_value(map=heap,ks=4,vs=10240)
    142: (b7) r5 = 8200                   ; R5_w=8200
    143: (85) call bpf_perf_event_output#25
    cannot pass map_type 27 into func bpf_perf_event_output#25

map_type 27 is BPF_MAP_TYPE_RINGBUF.

At the same time, I also moved the notification message (Tracing...) to
after all steps were successful.

Signed-off-by: Rong Tao <rongtao@cestc.cn>

Author: Rtoax

libbpf-tools/filelife.c

@@ -150,6 +150,13 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	buf = bpf_buffer__new(obj->maps.events, obj->maps.heap);
+	if (!buf) {
+		err = -errno;
+		fprintf(stderr, "failed to create ring/perf buffer: %d", err);
+		goto cleanup;
+	}
+
 	/* initialize global data (filtering options) */
 	obj->rodata->targ_tgid = env.pid;
 	obj->rodata->full_path = env.full_path;
@@ -169,16 +176,6 @@ int main(int argc, char **argv)
 		goto cleanup;
 	}
 
-	printf("Tracing the lifespan of short-lived files ... Hit Ctrl-C to end.\n");
-	printf("%-8s %-6s %-16s %-7s %s\n", "TIME", "PID", "COMM", "AGE(s)", "FILE");
-
-	buf = bpf_buffer__new(obj->maps.events, obj->maps.heap);
-	if (!buf) {
-		err = -errno;
-		fprintf(stderr, "failed to create ring/perf buffer: %d", err);
-		goto cleanup;
-	}
-
 	err = bpf_buffer__open(buf, handle_event, handle_lost_events, NULL);
 	if (err) {
 		err = -errno;
@@ -192,6 +189,9 @@ int main(int argc, char **argv)
 		goto cleanup;
 	}
 
+	printf("Tracing the lifespan of short-lived files ... Hit Ctrl-C to end.\n");
+	printf("%-8s %-6s %-16s %-7s %s\n", "TIME", "PID", "COMM", "AGE(s)", "FILE");
+
 	while (!exiting) {
 		err = bpf_buffer__poll(buf, POLL_TIMEOUT_MS);
 		if (err < 0 && err != -EINTR) {