[PATCH v6 2/5] selftests/resctrl: Add a helper for the non-contiguous test

[Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>]

The CAT non-contiguous selftests have to read the file responsible for
reporting support of non-contiguous CBMs in kernel (resctrl). Then the
test compares if that information matches what is reported by CPUID
output.

Add a generic helper function to read an unsigned number from
/sys/fs/resctrl/info/<RESOURCE>/<FILE>.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changelog v6:
- Add Reinette's reviewed-by tag.

Changelog v5:
- Remove '\n' from ksft_print_msg() calls. (Ilpo)
- Add Ilpo's reviewed-by tag.
- Change 'helpers' -> 'a helper' in the subject.
- Change 'a file in' -> '' in patch message.
- Remove '*' from resource_info_file_exists()'s comment.
- 'saved into the @val' -> 'saved into @val'
- 'Error in opening' -> 'Error opening'
- Redo path in function comment.

Changelog v4:
- Rewrite function comment.
- Redo ksft_perror() as ksft_print_msg(). (Reinette)

Changelog v3:
- Rewrite patch message.
- Add documentation and rewrote the function. (Reinette)

Changelog v2:
- Add this patch.

 tools/testing/selftests/resctrl/resctrl.h   |  1 +
 tools/testing/selftests/resctrl/resctrlfs.c | 36 +++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index a1462029998e..5116ea082d03 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -162,6 +162,7 @@ unsigned int count_contiguous_bits(unsigned long val, unsigned int *start);
 int get_full_cbm(const char *cache_type, unsigned long *mask);
 int get_mask_no_shareable(const char *cache_type, unsigned long *mask);
 int get_cache_size(int cpu_no, const char *cache_type, unsigned long *cache_size);
+int resource_info_unsigned_get(const char *resource, const char *filename, unsigned int *val);
 void ctrlc_handler(int signum, siginfo_t *info, void *ptr);
 int signal_handler_register(void);
 void signal_handler_unregister(void);
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 5750662cce57..8a183c73bc23 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -249,6 +249,42 @@ static int get_bit_mask(const char *filename, unsigned long *mask)
 	return 0;
 }
 
+/*
+ * resource_info_unsigned_get - Read an unsigned value from
+ * /sys/fs/resctrl/info/@resource/@filename
+ * @resource:	Resource name that matches directory name in
+ *		/sys/fs/resctrl/info
+ * @filename:	File in /sys/fs/resctrl/info/@resource
+ * @val:	Contains read value on success.
+ *
+ * Return: = 0 on success, < 0 on failure. On success the read
+ * value is saved into @val.
+ */
+int resource_info_unsigned_get(const char *resource, const char *filename,
+			       unsigned int *val)
+{
+	char file_path[PATH_MAX];
+	FILE *fp;
+
+	snprintf(file_path, sizeof(file_path), "%s/%s/%s", INFO_PATH, resource,
+		 filename);
+
+	fp = fopen(file_path, "r");
+	if (!fp) {
+		ksft_print_msg("Error opening %s: %m\n", file_path);
+		return -1;
+	}
+
+	if (fscanf(fp, "%u", val) <= 0) {
+		ksft_print_msg("Could not get contents of %s: %m\n", file_path);
+		fclose(fp);
+		return -1;
+	}
+
+	fclose(fp);
+	return 0;
+}
+
 /*
  * create_bit_mask- Create bit mask from start, len pair
  * @start:	LSB of the mask
-- 
2.43.0