[PATCH v6 0/2] selftests/resctrl: Bug fix and optimization

[PATCH v6 0/2] selftests/resctrl: Bug fix and optimization

[Maciej Wieczor-Retman]

Write_schemata() uses fprintf() to write a bitmask into a schemata file
inside resctrl FS. It checks fprintf() return value but it doesn't check
fclose() return value. Error codes from fprintf() such as write errors,
are buffered and flushed back to the user only after fclose() is executed
which means any invalid bitmask can be written into the schemata file.

Rewrite write_schemata() to use syscalls instead of stdio file
operations to avoid the buffering.

The resctrlfs.c defines functions that interact with the resctrl FS
while resctrl_val.c defines functions that perform measurements on
the cache. Run_benchmark() fits logically into the second file before
resctrl_val() that uses it.

Move run_benchmark() from resctrlfs.c to resctrl_val.c and remove
redundant part of the kernel-doc comment. Make run_benchmark() static
and remove it from the header file.

Patch series is based on [1] which is based on [2] which are based on
kselftest next branch.

Changelog v6:
- Align schema_len error checking with typical snprintf format.
  (Reinette)
- Initialize schema string for early return eventuality. (Reinette)

Changelog v5:
- Add Ilpo's reviewed-by tag to Patch 1/2.
- Reword patch messages slightly.
- Add error check to schema_len variable.

Changelog v4:
- Change git signature from Wieczor-Retman Maciej to Maciej
  Wieczor-Retman.
- Rebase onto [1] which is based on [2]. (Reinette)
- Add fcntl.h explicitly to provide glibc backward compatibility.
  (Reinette)

Changelog v3:
- Use snprintf() return value instead of strlen() in write_schemata().
  (Ilpo)
- Make run_benchmark() static and remove it from the header file.
  (Reinette)
- Add Ilpo's reviewed-by tag to Patch 2/2.
- Patch messages and cover letter rewording.

Changelog v2:
- Change sprintf() to snprintf() in write_schemata().
- Redo write_schemata() with syscalls instead of stdio functions.
- Fix typos and missing dots in patch messages.
- Branch printf attribute patch to a separate series.

[v1] https://lore.kernel.org/all/cover.1692880423.git.maciej.wieczor-retman@intel.com/
[v2] https://lore.kernel.org/all/cover.1693213468.git.maciej.wieczor-retman@intel.com/
[v3] https://lore.kernel.org/all/cover.1693575451.git.maciej.wieczor-retman@intel.com/
[v4] https://lore.kernel.org/all/cover.1695369120.git.maciej.wieczor-retman@intel.com/
[v5] https://lore.kernel.org/all/cover.1695975327.git.maciej.wieczor-retman@intel.com/

[1] https://lore.kernel.org/all/20231002094813.6633-1-ilpo.jarvinen@linux.intel.com/
[2] https://lore.kernel.org/all/20230904095339.11321-1-ilpo.jarvinen@linux.intel.com/

Maciej Wieczor-Retman (2):
  selftests/resctrl: Fix schemata write error check
  selftests/resctrl: Move run_benchmark() to a more fitting file

 tools/testing/selftests/resctrl/resctrl.h     |  1 -
 tools/testing/selftests/resctrl/resctrl_val.c | 50 +++++++++++
 tools/testing/selftests/resctrl/resctrlfs.c   | 88 +++++--------------
 3 files changed, 73 insertions(+), 66 deletions(-)

-- 
2.42.0

[PATCH v6 1/2] selftests/resctrl: Fix schemata write error check

[Maciej Wieczor-Retman]

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>
---
Changelog v6:
- Align schema_len error checking with typical snprintf format.
  (Reinette)
- Initialize schema string for early return eventuality. (Reinette)

Changelog v5:
- Add Ilpo's reviewed-by tag.
- Fix wrong open() error checking. (Reinette)
- Add error checking to schema_len variable.

Changelog v4:
- Unify error checking between open() and write(). (Reinette)
- Add fcntl.h for glibc backward compatiblitiy. (Reinette)

Changelog v3:
- Rename fp to fd. (Ilpo)
- Remove strlen, strcspn and just use the snprintf value instead. (Ilpo)

Changelog v2:
- Rewrite patch message.
- Double "reason" buffer size to fit longer error explanation.
- Redo file interactions with syscalls instead of stdio functions.

 tools/testing/selftests/resctrl/resctrlfs.c | 36 +++++++++++++--------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 3a8111362d26..648f9ec8b355 100644
--- 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 @@ int write_bm_pid_to_resctrl(pid_t bm_pid, char *ctrlgrp, char *mongrp,
  */
 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)) &&
@@ -520,27 +520,37 @@ 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);
+		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;
+	}
 
-	fp = fopen(controlgroup, "w");
-	if (!fp) {
-		sprintf(reason, "Failed to open control group");
+	fd = open(controlgroup, O_WRONLY);
+	if (fd < 0) {
+		snprintf(reason, sizeof(reason),
+			 "open() failed : %s", strerror(errno));
 		ret = -1;
 
 		goto out;
 	}
-
-	if (fprintf(fp, "%s\n", schema) < 0) {
-		sprintf(reason, "Failed to write schemata in control group");
-		fclose(fp);
+	if (write(fd, schema, schema_len) < 0) {
+		snprintf(reason, sizeof(reason),
+			 "write() failed : %s", strerror(errno));
+		close(fd);
 		ret = -1;
 
 		goto out;
 	}
-	fclose(fp);
+	close(fd);
+	schema[schema_len - 1] = 0;
 
 out:
 	ksft_print_msg("Write schema \"%s\" to resctrl FS%s%s\n",
-- 
2.42.0

[PATCH v6 2/2] selftests/resctrl: Move run_benchmark() to a more fitting file

[Maciej Wieczor-Retman]

resctrlfs.c contains mostly functions that interact in some way with
resctrl FS entries while functions inside resctrl_val.c deal with
measurements and benchmarking.

run_benchmark() is located in resctrlfs.c even though it's purpose
is not interacting with the resctrl FS but to execute cache checking
logic.

Move run_benchmark() to resctrl_val.c just before resctrl_val() that
makes use of run_benchmark(). Make run_benchmark() static since it's
not used between multiple files anymore.

Remove return comment from kernel-doc since the function is type void.

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 v4:
- Reword patch message very slightly. (Reinette)

Changelog v3:
- Make run_benchmark() static and remove it from the header. (Reinette)
- Remove return void kernel-doc comment. (Ilpo)
- Added Ilpo's reviewed-by tag.

 tools/testing/selftests/resctrl/resctrl.h     |  1 -
 tools/testing/selftests/resctrl/resctrl_val.c | 50 ++++++++++++++++++
 tools/testing/selftests/resctrl/resctrlfs.c   | 52 -------------------
 3 files changed, 50 insertions(+), 53 deletions(-)

diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 8578a8b4e145..a33f414f6019 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -86,7 +86,6 @@ int validate_bw_report_request(char *bw_report);
 bool validate_resctrl_feature_request(const char *resource, const char *feature);
 char *fgrep(FILE *inf, const char *str);
 int taskset_benchmark(pid_t bm_pid, int cpu_no);
-void run_benchmark(int signum, siginfo_t *info, void *ucontext);
 int write_schemata(char *ctrlgrp, char *schemata, int cpu_no,
 		   char *resctrl_val);
 int write_bm_pid_to_resctrl(pid_t bm_pid, char *ctrlgrp, char *mongrp,
diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
index a9fe61133119..0577e983067a 100644
--- a/tools/testing/selftests/resctrl/resctrl_val.c
+++ b/tools/testing/selftests/resctrl/resctrl_val.c
@@ -625,6 +625,56 @@ measure_vals(struct resctrl_val_param *param, unsigned long *bw_resc_start)
 	return 0;
 }
 
+/*
+ * run_benchmark - Run a specified benchmark or fill_buf (default benchmark)
+ *		   in specified signal. Direct benchmark stdio to /dev/null.
+ * @signum:	signal number
+ * @info:	signal info
+ * @ucontext:	user context in signal handling
+ */
+static void run_benchmark(int signum, siginfo_t *info, void *ucontext)
+{
+	int operation, ret, memflush;
+	char **benchmark_cmd;
+	size_t span;
+	bool once;
+	FILE *fp;
+
+	benchmark_cmd = info->si_ptr;
+
+	/*
+	 * Direct stdio of child to /dev/null, so that only parent writes to
+	 * stdio (console)
+	 */
+	fp = freopen("/dev/null", "w", stdout);
+	if (!fp)
+		PARENT_EXIT("Unable to direct benchmark status to /dev/null");
+
+	if (strcmp(benchmark_cmd[0], "fill_buf") == 0) {
+		/* Execute default fill_buf benchmark */
+		span = strtoul(benchmark_cmd[1], NULL, 10);
+		memflush =  atoi(benchmark_cmd[2]);
+		operation = atoi(benchmark_cmd[3]);
+		if (!strcmp(benchmark_cmd[4], "true"))
+			once = true;
+		else if (!strcmp(benchmark_cmd[4], "false"))
+			once = false;
+		else
+			PARENT_EXIT("Invalid once parameter");
+
+		if (run_fill_buf(span, memflush, operation, once))
+			fprintf(stderr, "Error in running fill buffer\n");
+	} else {
+		/* Execute specified benchmark */
+		ret = execvp(benchmark_cmd[0], benchmark_cmd);
+		if (ret)
+			perror("wrong\n");
+	}
+
+	fclose(stdout);
+	PARENT_EXIT("Unable to run specified benchmark");
+}
+
 /*
  * resctrl_val:	execute benchmark and measure memory bandwidth on
  *			the benchmark
diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
index 648f9ec8b355..e6d418fcf084 100644
--- a/tools/testing/selftests/resctrl/resctrlfs.c
+++ b/tools/testing/selftests/resctrl/resctrlfs.c
@@ -294,58 +294,6 @@ int taskset_benchmark(pid_t bm_pid, int cpu_no)
 	return 0;
 }
 
-/*
- * run_benchmark - Run a specified benchmark or fill_buf (default benchmark)
- *		   in specified signal. Direct benchmark stdio to /dev/null.
- * @signum:	signal number
- * @info:	signal info
- * @ucontext:	user context in signal handling
- *
- * Return: void
- */
-void run_benchmark(int signum, siginfo_t *info, void *ucontext)
-{
-	int operation, ret, memflush;
-	char **benchmark_cmd;
-	size_t span;
-	bool once;
-	FILE *fp;
-
-	benchmark_cmd = info->si_ptr;
-
-	/*
-	 * Direct stdio of child to /dev/null, so that only parent writes to
-	 * stdio (console)
-	 */
-	fp = freopen("/dev/null", "w", stdout);
-	if (!fp)
-		PARENT_EXIT("Unable to direct benchmark status to /dev/null");
-
-	if (strcmp(benchmark_cmd[0], "fill_buf") == 0) {
-		/* Execute default fill_buf benchmark */
-		span = strtoul(benchmark_cmd[1], NULL, 10);
-		memflush =  atoi(benchmark_cmd[2]);
-		operation = atoi(benchmark_cmd[3]);
-		if (!strcmp(benchmark_cmd[4], "true"))
-			once = true;
-		else if (!strcmp(benchmark_cmd[4], "false"))
-			once = false;
-		else
-			PARENT_EXIT("Invalid once parameter");
-
-		if (run_fill_buf(span, memflush, operation, once))
-			fprintf(stderr, "Error in running fill buffer\n");
-	} else {
-		/* Execute specified benchmark */
-		ret = execvp(benchmark_cmd[0], benchmark_cmd);
-		if (ret)
-			perror("wrong\n");
-	}
-
-	fclose(stdout);
-	PARENT_EXIT("Unable to run specified benchmark");
-}
-
 /*
  * create_grp - Create a group only if one doesn't exist
  * @grp_name:	Name of the group
-- 
2.42.0

Re: [PATCH v6 1/2] selftests/resctrl: Fix schemata write error check

[Reinette Chatre]

Hi Maciej,

On 10/9/2023 3:57 AM, Maciej Wieczor-Retman wrote:
> 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>
> ---
> Changelog v6:
> - Align schema_len error checking with typical snprintf format.
>   (Reinette)
> - Initialize schema string for early return eventuality. (Reinette)
> 
> Changelog v5:
> - Add Ilpo's reviewed-by tag.
> - Fix wrong open() error checking. (Reinette)
> - Add error checking to schema_len variable.
> 
> Changelog v4:
> - Unify error checking between open() and write(). (Reinette)
> - Add fcntl.h for glibc backward compatiblitiy. (Reinette)
> 
> Changelog v3:
> - Rename fp to fd. (Ilpo)
> - Remove strlen, strcspn and just use the snprintf value instead. (Ilpo)
> 
> Changelog v2:
> - Rewrite patch message.
> - Double "reason" buffer size to fit longer error explanation.
> - Redo file interactions with syscalls instead of stdio functions.
> 
>  tools/testing/selftests/resctrl/resctrlfs.c | 36 +++++++++++++--------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
> index 3a8111362d26..648f9ec8b355 100644
> --- 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 @@ int write_bm_pid_to_resctrl(pid_t bm_pid, char *ctrlgrp, char *mongrp,
>   */
>  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)) &&
> @@ -520,27 +520,37 @@ 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);
> +		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;
> +	}
>  
> -	fp = fopen(controlgroup, "w");
> -	if (!fp) {
> -		sprintf(reason, "Failed to open control group");
> +	fd = open(controlgroup, O_WRONLY);
> +	if (fd < 0) {
> +		snprintf(reason, sizeof(reason),
> +			 "open() failed : %s", strerror(errno));
>  		ret = -1;
>  
>  		goto out;
>  	}
> -
> -	if (fprintf(fp, "%s\n", schema) < 0) {
> -		sprintf(reason, "Failed to write schemata in control group");
> -		fclose(fp);
> +	if (write(fd, schema, schema_len) < 0) {
> +		snprintf(reason, sizeof(reason),
> +			 "write() failed : %s", strerror(errno));
> +		close(fd);
>  		ret = -1;
>  
>  		goto out;
>  	}
> -	fclose(fp);
> +	close(fd);
> +	schema[schema_len - 1] = 0;
>  
>  out:
>  	ksft_print_msg("Write schema \"%s\" to resctrl FS%s%s\n",


As changelog states, the newline is removed from schema to
ensure it is printed correctly. Note that this is not done when an
error is encountered during open() or write() so when an error is
encountered in these places then the print does not look as intended.

I think a new goto label inserted just before the newline removal
should be sufficient, with the open() and write() error paths jumping
to it.

With that addressed:

Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reinette

Re: [PATCH v6 1/2] selftests/resctrl: Fix schemata write error check

[Maciej Wieczór-Retman]

On 2023-10-09 at 11:55:16 -0700, Reinette Chatre wrote:
>Hi Maciej,
>
>On 10/9/2023 3:57 AM, Maciej Wieczor-Retman wrote:
>> 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>
>> ---
>> Changelog v6:
>> - Align schema_len error checking with typical snprintf format.
>>   (Reinette)
>> - Initialize schema string for early return eventuality. (Reinette)
>> 
>> Changelog v5:
>> - Add Ilpo's reviewed-by tag.
>> - Fix wrong open() error checking. (Reinette)
>> - Add error checking to schema_len variable.
>> 
>> Changelog v4:
>> - Unify error checking between open() and write(). (Reinette)
>> - Add fcntl.h for glibc backward compatiblitiy. (Reinette)
>> 
>> Changelog v3:
>> - Rename fp to fd. (Ilpo)
>> - Remove strlen, strcspn and just use the snprintf value instead. (Ilpo)
>> 
>> Changelog v2:
>> - Rewrite patch message.
>> - Double "reason" buffer size to fit longer error explanation.
>> - Redo file interactions with syscalls instead of stdio functions.
>> 
>>  tools/testing/selftests/resctrl/resctrlfs.c | 36 +++++++++++++--------
>>  1 file changed, 23 insertions(+), 13 deletions(-)
>> 
>> diff --git a/tools/testing/selftests/resctrl/resctrlfs.c b/tools/testing/selftests/resctrl/resctrlfs.c
>> index 3a8111362d26..648f9ec8b355 100644
>> --- 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 @@ int write_bm_pid_to_resctrl(pid_t bm_pid, char *ctrlgrp, char *mongrp,
>>   */
>>  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)) &&
>> @@ -520,27 +520,37 @@ 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);
>> +		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;
>> +	}
>>  
>> -	fp = fopen(controlgroup, "w");
>> -	if (!fp) {
>> -		sprintf(reason, "Failed to open control group");
>> +	fd = open(controlgroup, O_WRONLY);
>> +	if (fd < 0) {
>> +		snprintf(reason, sizeof(reason),
>> +			 "open() failed : %s", strerror(errno));
>>  		ret = -1;
>>  
>>  		goto out;
>>  	}
>> -
>> -	if (fprintf(fp, "%s\n", schema) < 0) {
>> -		sprintf(reason, "Failed to write schemata in control group");
>> -		fclose(fp);
>> +	if (write(fd, schema, schema_len) < 0) {
>> +		snprintf(reason, sizeof(reason),
>> +			 "write() failed : %s", strerror(errno));
>> +		close(fd);
>>  		ret = -1;
>>  
>>  		goto out;
>>  	}
>> -	fclose(fp);
>> +	close(fd);
>> +	schema[schema_len - 1] = 0;
>>  
>>  out:
>>  	ksft_print_msg("Write schema \"%s\" to resctrl FS%s%s\n",
>
>
>As changelog states, the newline is removed from schema to
>ensure it is printed correctly. Note that this is not done when an
>error is encountered during open() or write() so when an error is
>encountered in these places then the print does not look as intended.
>
>I think a new goto label inserted just before the newline removal
>should be sufficient, with the open() and write() error paths jumping
>to it.
>
>With that addressed:
>
>Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
>
>Reinette

Thanks, I'll make the correction and resend.

-- 
Kind regards
Maciej Wieczór-Retman