rtla: Fix -C/--cgroup interface

Currently, user can only specify cgroup to the tracer's thread the
following ways:

    `-C[cgroup]`
    `-C[=cgroup]`
    `--cgroup[=cgroup]`

If user tries to specify cgroup as `-C [cgroup]` or `--cgroup [cgroup]`,
the parser silently fails and rtla's cgroup is used for the tracer
threads.

To make interface more user-friendly, allow user to specify cgroup in
the aforementioned way, i.e. `-C [cgroup]` and `--cgroup [cgroup]`.

Refactor identical logic between -t/--trace and -C/--cgroup into a
common function.

Change documentation to reflect this user interface change.

Fixes: a957cbc02531 ("rtla: Add -C cgroup support")
Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>
Reviewed-by: Tomas Glozar <tglozar@redhat.com>
Link: https://lore.kernel.org/r/16132f1565cf5142b5fbd179975be370b529ced7.1762186418.git.ipravdin.official@gmail.com
[ use capital letter in subject, as required by tracing subsystem ]
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
index 54334c676a22..9cf5a0098e9a 100644
--- a/tools/tracing/rtla/src/utils.c
+++ b/tools/tracing/rtla/src/utils.c
@@ -974,3 +974,29 @@ int auto_house_keeping(cpu_set_t *monitored_cpus)
 
 	return 1;
 }
+
+/**
+ * parse_optional_arg - Parse optional argument value
+ *
+ * Parse optional argument value, which can be in the form of:
+ * -sarg, -s/--long=arg, -s/--long arg
+ *
+ * Returns arg value if found, NULL otherwise.
+ */
+char *parse_optional_arg(int argc, char **argv)
+{
+	if (optarg) {
+		if (optarg[0] == '=') {
+			/* skip the = */
+			return &optarg[1];
+		} else {
+			return optarg;
+		}
+	/* parse argument of form -s [arg] and --long [arg]*/
+	} else if (optind < argc && argv[optind][0] != '-') {
+		/* consume optind */
+		return argv[optind++];
+	} else {
+		return NULL;
+	}
+}