[PATCH v3 18/21] selftests/resctrl: Fix incorrect parsing of iMC counters

[Fenghua Yu]

iMC (Integrated Memory Controller) counters are usually at
"/sys/bus/event_source/devices/" and are named as "uncore_imc_<n>".
num_of_imcs() function tries to count number of such iMC counters so that
it could appropriately initialize required number of perf_attr structures
that could be used to read these iMC counters.

num_of_imcs() function assumes that all the directories under this path
that start with "uncore_imc" are iMC counters. But, on some systems there
could be directories named as "uncore_imc_free_running" which aren't iMC
counters. Trying to read from such directories will result in "not found
file" errors and MBM/MBA tests will fail.

Hence, fix the logic in num_of_imcs() such that it looks at the first
character after "uncore_imc_" to check if it's a numerical digit or not. If
it's a digit then the directory represents an iMC counter, else, skip the
directory.

Fixes: 7f4d257e3a2a ("selftests/resctrl: Add callback to start a benchmark")
Reported-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 tools/testing/selftests/resctrl/resctrl_val.c | 22 +++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
index 270cd95e0026..88f9b641d753 100644
--- a/tools/testing/selftests/resctrl/resctrl_val.c
+++ b/tools/testing/selftests/resctrl/resctrl_val.c
@@ -221,8 +221,8 @@ static int read_from_imc_dir(char *imc_dir, int count)
  */
 static int num_of_imcs(void)
 {
+	char imc_dir[512], *temp;
 	unsigned int count = 0;
-	char imc_dir[512];
 	struct dirent *ep;
 	int ret;
 	DIR *dp;
@@ -230,7 +230,25 @@ static int num_of_imcs(void)
 	dp = opendir(DYN_PMU_PATH);
 	if (dp) {
 		while ((ep = readdir(dp))) {
-			if (strstr(ep->d_name, UNCORE_IMC)) {
+			temp = strstr(ep->d_name, UNCORE_IMC);
+			if (!temp)
+				continue;
+
+			/*
+			 * imc counters are named as "uncore_imc_<n>", hence
+			 * increment the pointer to point to <n>. Note that
+			 * sizeof(UNCORE_IMC) would count for null character as
+			 * well and hence the last underscore character in
+			 * uncore_imc'_' need not be counted.
+			 */
+			temp = temp + sizeof(UNCORE_IMC);
+
+			/*
+			 * Some directories under "DYN_PMU_PATH" could have
+			 * names like "uncore_imc_free_running", hence, check if
+			 * first character is a numerical digit or not.
+			 */
+			if (temp[0] >= '0' && temp[0] <= '9') {
 				sprintf(imc_dir, "%s/%s/", DYN_PMU_PATH,
 					ep->d_name);
 				ret = read_from_imc_dir(imc_dir, count);
-- 
2.29.0