[PATCH v5 13/16] selftests/resctrl: Convert ctrlgrp & mongrp to pointers

[Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>]

The struct resctrl_val_param has control and monitor groups as char
arrays but they are not supposed to be mutated within resctrl_val().

Convert the ctrlgrp and mongrp char array within resctrl_val_param to
plain const char pointers and adjust the strlen() based checks to
check NULL instead.

Convert !grp_name check in create_grp() into internal sanity check by
returning error if the caller asked to create a group but doesn't
provide a name for the group. The existing code already abides this by
only calling create_grp() if mongrp is non-NULL so the error should
never be returned with the current selftests (ctrlgrp is never NULL).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
---
v5:
- Return 0 if grp_name is null (restore earlier behavior)
- Move the root group note from comment into kerneldoc

v3:
- Removed wrong comment
- Changed grp_name check to return -1 on fail (internal sanity check)
---
 tools/testing/selftests/resctrl/resctrl.h   |  4 ++--
 tools/testing/selftests/resctrl/resctrlfs.c | 16 +++++++---------
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 5967389038d4..a999fbc13fd3 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -91,8 +91,8 @@ struct resctrl_test {
  */
 struct resctrl_val_param {
 	char		*resctrl_val;
-	char		ctrlgrp[64];
-	char		mongrp[64];
+	const char	*ctrlgrp;
+	const char	*mongrp;
 	char		filename[64];
 	unsigned long	mask;
 	int		num_of_runs;
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index f4dc8ef23a8c..893041faaf18 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -456,6 +456,9 @@ int taskset_restore(pid_t bm_pid, cpu_set_t *old_affinity)
  * @grp:	Full path and name of the group
  * @parent_grp:	Full path and name of the parent group
  *
+ * Creates a group @grp_name if it does not exist yet. If @grp_name is NULL,
+ * it is interpreted as the root group which always results success.
+ *
  * Return: 0 on success, < 0 on error.
  */
 static int create_grp(const char *grp_name, char *grp, const char *parent_grp)
@@ -464,12 +467,7 @@ static int create_grp(const char *grp_name, char *grp, const char *parent_grp)
 	struct dirent *ep;
 	DIR *dp;
 
-	/*
-	 * At this point, we are guaranteed to have resctrl FS mounted and if
-	 * length of grp_name == 0, it means, user wants to use root con_mon
-	 * grp, so do nothing
-	 */
-	if (strlen(grp_name) == 0)
+	if (!grp_name)
 		return 0;
 
 	/* Check if requested grp exists or not */
@@ -541,7 +539,7 @@ int write_bm_pid_to_resctrl(pid_t bm_pid, const char *ctrlgrp,
 	char tasks[1024];
 	int ret = 0;
 
-	if (strlen(ctrlgrp))
+	if (ctrlgrp)
 		sprintf(controlgroup, "%s/%s", RESCTRL_PATH, ctrlgrp);
 	else
 		sprintf(controlgroup, "%s", RESCTRL_PATH);
@@ -558,7 +556,7 @@ int write_bm_pid_to_resctrl(pid_t bm_pid, const char *ctrlgrp,
 	/* Create mon grp and write pid into it for "mbm" and "cmt" test */
 	if (!strncmp(resctrl_val, CMT_STR, sizeof(CMT_STR)) ||
 	    !strncmp(resctrl_val, MBM_STR, sizeof(MBM_STR))) {
-		if (strlen(mongrp)) {
+		if (mongrp) {
 			sprintf(monitorgroup_p, "%s/mon_groups", controlgroup);
 			sprintf(monitorgroup, "%s/%s", monitorgroup_p, mongrp);
 			ret = create_grp(mongrp, monitorgroup, monitorgroup_p);
@@ -612,7 +610,7 @@ int write_schemata(const char *ctrlgrp, char *schemata, int cpu_no,
 		goto out;
 	}
 
-	if (strlen(ctrlgrp) != 0)
+	if (ctrlgrp)
 		sprintf(controlgroup, "%s/%s/schemata", RESCTRL_PATH, ctrlgrp);
 	else
 		sprintf(controlgroup, "%s/schemata", RESCTRL_PATH);
-- 
2.39.2