[PATCH v3 04/10] perf record: Switch user option to use BPF filter

[Ian Rogers <irogers@google.com>]

The existing --uid option finds user processes by scanning
/proc. Scanning /proc is inherently racy due to processes being in
/proc but then exiting before perf does the perf_event_open. When the
perf_event_open fails perf will terminate reporting errors which is a
disappointing user experience. Scanning /proc when perf starts also
cannot inform perf of new user processes starting.

The ability to filter perf events with BPF isn't new, and has been in
the perf tool for 10 years:
https://lore.kernel.org/all/1444826502-49291-8-git-send-email-wangnan0@huawei.com/
An ability to do filtering on the command line with a BPF program
that's part of perf was added 2 years ago:
https://lore.kernel.org/all/20230314234237.3008956-1-namhyung@kernel.org/
This was then extended to support uids as a way of filtering:
https://lore.kernel.org/all/20240524205227.244375-1-irogers@google.com/

This change switches the perf record --uid option to use the BPF
filter code to avoid the inherent race and existing failures. To
ensure all processes are considered by the filter, the change forces
system-wide mode.

Using BPF has permission issues in loading the BPF program not present
in scanning /proc. As the scanning approach would miss new programs
and fail due to the race, this is considered preferable. The change
also avoids opening a perf event per PID, which is less overhead in
the kernel.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/builtin-record.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 7b64013ba8c0..5eddf3568b04 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -174,6 +174,7 @@ struct record {
 	bool			timestamp_boundary;
 	bool			off_cpu;
 	const char		*filter_action;
+	const char		*uid_str;
 	struct switch_output	switch_output;
 	unsigned long long	samples;
 	unsigned long		output_max_size;	/* = 0: unlimited */
@@ -3465,8 +3466,7 @@ static struct option __record_options[] = {
 		     "or ranges of time to enable events e.g. '-D 10-20,30-40'",
 		     record__parse_event_enable_time),
 	OPT_BOOLEAN(0, "kcore", &record.opts.kcore, "copy /proc/kcore"),
-	OPT_STRING('u', "uid", &record.opts.target.uid_str, "user",
-		   "user to profile"),
+	OPT_STRING('u', "uid", &record.uid_str, "user", "user to profile"),
 
 	OPT_CALLBACK_NOOPT('b', "branch-any", &record.opts.branch_stack,
 		     "branch any", "sample any taken branches",
@@ -4205,19 +4205,24 @@ int cmd_record(int argc, const char **argv)
 		ui__warning("%s\n", errbuf);
 	}
 
-	err = target__parse_uid(&rec->opts.target);
-	if (err) {
-		int saved_errno = errno;
+	if (rec->uid_str) {
+		uid_t uid = parse_uid(rec->uid_str);
 
-		target__strerror(&rec->opts.target, err, errbuf, BUFSIZ);
-		ui__error("%s", errbuf);
+		if (uid == UINT_MAX) {
+			ui__error("Invalid User: %s", rec->uid_str);
+			err = -EINVAL;
+			goto out;
+		}
+		err = parse_uid_filter(rec->evlist, uid);
+		if (err)
+			goto out;
 
-		err = -saved_errno;
-		goto out;
+		/* User ID filtering implies system wide. */
+		rec->opts.target.system_wide = true;
 	}
 
-	/* Enable ignoring missing threads when -u/-p option is defined. */
-	rec->opts.ignore_missing_thread = rec->opts.target.uid != UINT_MAX || rec->opts.target.pid;
+	/* Enable ignoring missing threads when -p option is defined. */
+	rec->opts.ignore_missing_thread = rec->opts.target.pid;
 
 	evlist__warn_user_requested_cpus(rec->evlist, rec->opts.target.cpu_list);
 
-- 
2.49.0.850.g28803427d3-goog