From b48543c451c30387b53ee6e202dda8d5303f6268 Mon Sep 17 00:00:00 2001 From: Tiezhu Yang Date: Tue, 30 Jul 2024 14:23:01 +0800 Subject: [PATCH] perf list: Give clues if failed to open tracing events directory When executing the command "perf list", I met "Error: failed to open tracing events directory" twice, the first reason is that there is no "/sys/kernel/tracing/events" directory due to it does not enable the kernel tracing infrastructure with CONFIG_FTRACE, the second reason is that there is no root privileges. Add the error string to tell the users what happened and what should to do, and also call put_tracing_file() to free events_path a little later to avoid messy code in the error message. At the same time, just remove the redundant "/" of the file path in the function get_tracing_file(), otherwise it shows something like "/sys/kernel/tracing//events". Before: $ ./perf list Error: failed to open tracing events directory After: (1) Without CONFIG_FTRACE $ ./perf list Error: failed to open tracing events directory /sys/kernel/tracing/events: No such file or directory (2) With CONFIG_FTRACE but no root privileges $ ./perf list Error: failed to open tracing events directory /sys/kernel/tracing/events: Permission denied Committer testing: Redirect stdout to null to quickly test the patch: Before: $ perf list > /dev/null Error: failed to open tracing events directory $ After: $ perf list > /dev/null Error: failed to open tracing events directory /sys/kernel/tracing/events: Permission denied $ Signed-off-by: Tiezhu Yang Tested-by: Arnaldo Carvalho de Melo Cc: Ingo Molnar Cc: Namhyung Kim Cc: Peter Zijlstra Link: https://lore.kernel.org/lkml/20240730062301.23244-3-yangtiezhu@loongson.cn Signed-off-by: Arnaldo Carvalho de Melo --- tools/lib/api/fs/tracing_path.c | 2 +- tools/perf/util/print-events.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/tools/lib/api/fs/tracing_path.c b/tools/lib/api/fs/tracing_path.c index 30745f35d0d2..834fd64c7130 100644 --- a/tools/lib/api/fs/tracing_path.c +++ b/tools/lib/api/fs/tracing_path.c @@ -69,7 +69,7 @@ char *get_tracing_file(const char *name) { char *file; - if (asprintf(&file, "%s/%s", tracing_path_mount(), name) < 0) + if (asprintf(&file, "%s%s", tracing_path_mount(), name) < 0) return NULL; return file; diff --git a/tools/perf/util/print-events.c b/tools/perf/util/print-events.c index 3f38c27f0157..81e0135cddf0 100644 --- a/tools/perf/util/print-events.c +++ b/tools/perf/util/print-events.c @@ -68,11 +68,12 @@ void print_tracepoint_events(const struct print_callbacks *print_cb __maybe_unus struct dirent **sys_namelist = NULL; int sys_items; - put_tracing_file(events_path); if (events_fd < 0) { pr_err("Error: failed to open tracing events directory\n"); + pr_err("%s: %s\n", events_path, strerror(errno)); return; } + put_tracing_file(events_path); sys_items = tracing_events__scandir_alphasort(&sys_namelist); -- 2.20.1