Re: [PATCH v2 6/8] deadline_test.c: Check return values of write() and ftruncate()

[John Kacur <jkacur@redhat.com>]

On Sat, 26 Jul 2025, Cheng-Yang Chou wrote:

> Add error handling for write() to tracefs, cpuset control files, and
> system() calls to avoid ignoring errors.
> 
> Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
> ---
>  src/sched_deadline/deadline_test.c | 37 ++++++++++++++++++++++++++----
>  1 file changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/src/sched_deadline/deadline_test.c b/src/sched_deadline/deadline_test.c
> index ca2da47..a74d514 100644
> --- a/src/sched_deadline/deadline_test.c
> +++ b/src/sched_deadline/deadline_test.c
> @@ -325,6 +325,7 @@ static void ftrace_write(char *buf, const char *fmt, ...)
>  {
>  	va_list ap;
>  	int n;
> +	int ret;
>  
>  	if (mark_fd < 0)
>  		return;
> @@ -333,7 +334,9 @@ static void ftrace_write(char *buf, const char *fmt, ...)
>  	n = my_vsprintf(buf, BUFSIZ, fmt, ap);
>  	va_end(ap);
>  
> -	write(mark_fd, buf, n);
> +	ret = write(mark_fd, buf, n);
> +	if (ret < 0)
> +		perror("ftrace write failed");
>  }
>  
>  /**
> @@ -626,6 +629,10 @@ static int mount_cpuset(void)
>  	if (fd < 0)
>  		return fd;
>  	ret = write(fd, "0", 2);
> +	if (ret < 0) {
> +		close(fd);
> +		return ret;
> +	}
>  	close(fd);
>  
>  	return 0;
> @@ -875,7 +882,19 @@ static void destroy_cpuset(const char *name, int print)
>  		sprintf(buf, "%d", pid);
>  		if (print)
>  			printf("Moving %d out of %s\n", pid, name);
> -		write(fd, buf, strlen(buf));
> +		ret = write(fd, buf, strlen(buf));
> +		if (ret < 0 && errno == ENOSPC) {
> +			/*
> +			 * If we get ENOSPC, then we have a problem, as it
> +			 * means that the cpuset is full, and we cannot move
> +			 * the tasks out of it.
> +			 */
> +			fclose(fp);
> +			close(fd);
> +			fprintf(stderr, "Failed to move %d out of %s\n", pid, name);
> +			perror("write");
> +			return;
> +		}
>  	}
>  	fclose(fp);
>  	close(fd);
> @@ -910,16 +929,21 @@ static void destroy_cpuset(const char *name, int print)
>  static void teardown(void)
>  {
>  	int fd;
> +	int ret;
>  
>  	fd = open_cpuset(CPUSET_PATH, "cpuset.cpu_exclusive");
>  	if (fd >= 0) {
> -		write(fd, "0", 2);
> +		ret = write(fd, "0", 2);
> +		if (ret < 0)
> +			perror("cpuset.cpu_exclusive");
>  		close(fd);
>  	}
>  
>  	fd = open_cpuset(CPUSET_PATH, "cpuset.sched_load_balance");
>  	if (fd >= 0) {
> -		write(fd, "1", 2);
> +		ret = write(fd, "1", 2);
> +		if (ret < 0)
> +			perror("cpuset.sched_load_balance");
>  		close(fd);
>  	}
>  
> @@ -1790,6 +1814,7 @@ int main(int argc, char **argv)
>  	int rt_task = 0;
>  	int i;
>  	int c;
> +	int ret;
>  
>  	cpu_count = sysconf(_SC_NPROCESSORS_CONF);
>  	if (cpu_count < 1) {
> @@ -2041,7 +2066,9 @@ int main(int argc, char **argv)
>  			exit(-1);
>  		}
>  
> -		system("cat /sys/fs/cgroup/cpuset/my_cpuset/tasks");
> +		ret = system("cat /sys/fs/cgroup/cpuset/my_cpuset/tasks");
> +		if (ret < 0)
> +			perror("system call failed");
>  	}
>  
>  	pthread_barrier_wait(&barrier);
> -- 
> 2.48.1
> 
> 
> 
Signed-off-by: John Kacur <jkacur@redhat.com>