perf evlist: Refactor evlist__scnprintf_evsels()

Switch output to using a strbuf so the storage can be resized.

Add a maximum size argument to avoid too much output that may happen for
uncore events.

Rename as scnprintf is no longer used.

Committer testing:

  With the patch applied:

  root@number:~# perf probe -x ~/bin/perf evlist__format_evsels
  Added new event:
    probe_perf:evlist_format_evsels (on evlist__format_evsels in /home/acme/bin/perf)

  You can now use it in all perf tools, such as:

  	perf record -e probe_perf:evlist_format_evsels -aR sleep 1

  root@number:~# perf probe -l
    probe_perf:evlist_format_evsels (on evlist__format_evsels@util/evlist.c in /home/acme/bin/perf)
  root@number:~# perf trace -e probe_perf:*/max-stack=10/ perf record -e cycles,instructions,cache-misses /tmp/bla
  Failed to collect 'cycles,instructions,cache-misses' for the '/tmp/bla' workload: Permission denied
       0.000 perf/3893011 probe_perf:evlist_format_evsels(__probe_ip: 6183397)
                                         evlist__format_evsels (/home/acme/bin/perf)
                                         __cmd_record (/home/acme/bin/perf)
                                         cmd_record (/home/acme/bin/perf)
                                         run_builtin (/home/acme/bin/perf)
                                         handle_internal_command (/home/acme/bin/perf)
                                         run_argv (/home/acme/bin/perf)
                                         main (/home/acme/bin/perf)
                                         __libc_start_call_main (/usr/lib64/libc.so.6)
                                         __libc_start_main@@GLIBC_2.34 (/usr/lib64/libc.so.6)
                                         _start (/home/acme/bin/perf)
  root@number:~#

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dominique Martinet <asmadeus@codewreck.org>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Levi Yun <yeoreum.yun@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Weilin Wang <weilin.wang@intel.com>
Link: https://lore.kernel.org/r/20250402201549.4090305-4-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 20 insertions, 13 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 8898357325cf..52cebacc19a7 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -51,6 +51,7 @@
 #include "util/clockid.h"
 #include "util/off_cpu.h"
 #include "util/bpf-filter.h"
+#include "util/strbuf.h"
 #include "asm/bug.h"
 #include "perf.h"
 #include "cputopo.h"
@@ -2791,13 +2792,15 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		record__auxtrace_snapshot_exit(rec);
 
 	if (forks && workload_exec_errno) {
-		char msg[STRERR_BUFSIZE], strevsels[2048];
+		char msg[STRERR_BUFSIZE];
 		const char *emsg = str_error_r(workload_exec_errno, msg, sizeof(msg));
+		struct strbuf sb = STRBUF_INIT;
 
-		evlist__scnprintf_evsels(rec->evlist, sizeof(strevsels), strevsels);
+		evlist__format_evsels(rec->evlist, &sb, 2048);
 
 		pr_err("Failed to collect '%s' for the '%s' workload: %s\n",
-			strevsels, argv[0], emsg);
+			sb.buf, argv[0], emsg);
+		strbuf_release(&sb);
 		err = -1;
 		goto out_child;
 	}
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 0a21da4f990f..140ac3ba8c11 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -35,6 +35,7 @@
 #include "util/util.h"
 #include "util/env.h"
 #include "util/intel-tpebs.h"
+#include "util/strbuf.h"
 #include <signal.h>
 #include <unistd.h>
 #include <sched.h>
@@ -2467,23 +2468,25 @@ struct evsel *evlist__find_evsel(struct evlist *evlist, int idx)
 	return NULL;
 }
 
-int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf)
+void evlist__format_evsels(struct evlist *evlist, struct strbuf *sb, size_t max_length)
 {
 	struct evsel *evsel;
-	int printed = 0;
+	bool first = true;
 
 	evlist__for_each_entry(evlist, evsel) {
 		if (evsel__is_dummy_event(evsel))
 			continue;
-		if (size > (strlen(evsel__name(evsel)) + (printed ? 2 : 1))) {
-			printed += scnprintf(bf + printed, size - printed, "%s%s", printed ? "," : "", evsel__name(evsel));
-		} else {
-			printed += scnprintf(bf + printed, size - printed, "%s...", printed ? "," : "");
-			break;
+
+		if (!first)
+			strbuf_addch(sb, ',');
+
+		if (sb->len > max_length) {
+			strbuf_addstr(sb, "...");
+			return;
 		}
+		strbuf_addstr(sb, evsel__name(evsel));
+		first = false;
 	}
-
-	return printed;
 }
 
 void evlist__check_mem_load_aux(struct evlist *evlist)
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index edcbf1c10e92..21f6bff319fd 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -20,6 +20,7 @@ struct pollfd;
 struct thread_map;
 struct perf_cpu_map;
 struct record_opts;
+struct strbuf;
 struct target;
 
 /*
@@ -430,7 +431,7 @@ int event_enable_timer__process(struct event_enable_timer *eet);
 
 struct evsel *evlist__find_evsel(struct evlist *evlist, int idx);
 
-int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf);
+void evlist__format_evsels(struct evlist *evlist, struct strbuf *sb, size_t max_length);
 void evlist__check_mem_load_aux(struct evlist *evlist);
 void evlist__warn_user_requested_cpus(struct evlist *evlist, const char *cpu_list);
 void evlist__uniquify_name(struct evlist *evlist);