selftests/resctrl: Fix schemata write error check

Writing bitmasks to the schemata can fail when the bitmask doesn't
adhere to constraints defined by what a particular CPU supports.
Some example of constraints are max length or having contiguous bits.
The driver should properly return errors when any rule concerning
bitmask format is broken.

Resctrl FS returns error codes from fprintf() only when fclose() is
called. Current error checking scheme allows invalid bitmasks to be
written into schemata file and the selftest doesn't notice because the
fclose() error code isn't checked.

Substitute fopen(), flose() and fprintf() with open(), close() and
write() to avoid error code buffering between fprintf() and fclose().

Remove newline character from the schema string after writing it to
the schemata file so it prints correctly before function return.

Pass the string generated with strerror() to the "reason" buffer so
the error message is more verbose. Extend "reason" buffer so it can hold
longer messages.

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>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 3a8111362d262b161faa5297cf708a95c1f1afdf..05390afd4d6f9f265231cc43aa2425cf3b7c5b70 100644 (file)
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -8,6 +8,7 @@
  *    Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
  *    Fenghua Yu <fenghua.yu@intel.com>
  */
+#include <fcntl.h>
 #include <limits.h>
 
 #include "resctrl.h"
@@ -490,9 +491,8 @@ out:
  */
 int write_schemata(char *ctrlgrp, char *schemata, int cpu_no, char *resctrl_val)
 {
-       char controlgroup[1024], schema[1024], reason[64];
-       int resource_id, ret = 0;
-       FILE *fp;
+       char controlgroup[1024], reason[128], schema[1024] = {};
+       int resource_id, fd, schema_len = -1, ret = 0;
 
        if (strncmp(resctrl_val, MBA_STR, sizeof(MBA_STR)) &&
            strncmp(resctrl_val, MBM_STR, sizeof(MBM_STR)) &&
@@ -520,28 +520,39 @@ int write_schemata(char *ctrlgrp, char *schemata, int cpu_no, char *resctrl_val)
 
        if (!strncmp(resctrl_val, CAT_STR, sizeof(CAT_STR)) ||
            !strncmp(resctrl_val, CMT_STR, sizeof(CMT_STR)))
-               sprintf(schema, "%s%d%c%s", "L3:", resource_id, '=', schemata);
+               schema_len = snprintf(schema, sizeof(schema), "%s%d%c%s\n",
+                                     "L3:", resource_id, '=', schemata);
        if (!strncmp(resctrl_val, MBA_STR, sizeof(MBA_STR)) ||
            !strncmp(resctrl_val, MBM_STR, sizeof(MBM_STR)))
-               sprintf(schema, "%s%d%c%s", "MB:", resource_id, '=', schemata);
-
-       fp = fopen(controlgroup, "w");
-       if (!fp) {
-               sprintf(reason, "Failed to open control group");
+               schema_len = snprintf(schema, sizeof(schema), "%s%d%c%s\n",
+                                     "MB:", resource_id, '=', schemata);
+       if (schema_len < 0 || schema_len >= sizeof(schema)) {
+               snprintf(reason, sizeof(reason),
+                        "snprintf() failed with return value : %d", schema_len);
                ret = -1;
-
                goto out;
        }
 
-       if (fprintf(fp, "%s\n", schema) < 0) {
-               sprintf(reason, "Failed to write schemata in control group");
-               fclose(fp);
+       fd = open(controlgroup, O_WRONLY);
+       if (fd < 0) {
+               snprintf(reason, sizeof(reason),
+                        "open() failed : %s", strerror(errno));
                ret = -1;
 
-               goto out;
+               goto err_schema_not_empty;
        }
-       fclose(fp);
+       if (write(fd, schema, schema_len) < 0) {
+               snprintf(reason, sizeof(reason),
+                        "write() failed : %s", strerror(errno));
+               close(fd);
+               ret = -1;
+
+               goto err_schema_not_empty;
+       }
+       close(fd);
 
+err_schema_not_empty:
+       schema[schema_len - 1] = 0;
 out:
        ksft_print_msg("Write schema \"%s\" to resctrl FS%s%s\n",
                       schema, ret ? " # " : "",