Re: [PATCH 2/2] cyclictest: simplify rstat_setup

On Sun, 1 Mar 2026, Lukas Beckmann wrote:

> The shm file is truncated to zero each time before it is written.
> It does not make sense to truncate it to something non zero on setup or
> to mlock it.
> 
> Signed-off-by: Lukas Beckmann <[email protected]>
> ---
>  src/cyclictest/cyclictest.c | 89 ++++++-------------------------------
>  1 file changed, 13 insertions(+), 76 deletions(-)
> 
> diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
> index 960c905..7b959ac 100644
> --- a/src/cyclictest/cyclictest.c
> +++ b/src/cyclictest/cyclictest.c
> @@ -1771,33 +1771,6 @@ static void trigger_update(struct thread_param *par, int diff, int64_t ts)
>  	pthread_mutex_unlock(&trigger_lock);
>  }
>  
> -/* Running status shared memory open */
> -static int rstat_shm_open(void)
> -{
> -	int fd;
> -	pid_t pid;
> -
> -	pid = getpid();
> -
> -	snprintf(shm_name, SHM_BUF_SIZE, "%s%d", "/cyclictest", pid);
> -
> -	errno = 0;
> -	fd = shm_unlink(shm_name);
> -
> -	if ((fd == -1) && (errno != ENOENT)) {
> -		fprintf(stderr, "ERROR: shm_unlink %s\n", strerror(errno));
> -		return fd;
> -	}
> -
> -	errno = 9;
> -	fd = shm_open(shm_name, O_RDWR|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH);
> -	if (fd == -1)
> -		fprintf(stderr, "ERROR: shm_open %s\n", strerror(errno));
> -
> -	rstat_fd = fd;
> -
> -	return fd;
> -}
>  
>  static int rstat_ftruncate(int fd, off_t len)
>  {
> @@ -1811,62 +1784,26 @@ static int rstat_ftruncate(int fd, off_t len)
>  	return err;
>  }
>  
> -static void *rstat_mmap(int fd)
> -{
> -	void *mptr;
>  
> -	errno = 0;
> -	mptr = mmap(0, _SC_PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
> +static void rstat_setup(void)
> +{
> +	int fd;
> +	pid_t pid;
>  
> -	if (mptr == (void*)-1)
> -		fprintf(stderr, "ERROR: mmap, %s\n", strerror(errno));
> +	pid = getpid();
>  
> -	return mptr;
> -}
> +	snprintf(shm_name, SHM_BUF_SIZE, "%s%d", "/cyclictest", pid);
>  
> -static int rstat_mlock(void *mptr)
> -{
> -	int err;

errno = 0 before the call to shm_unlink for good defensive programming
other than that the patch looks good, I will do a little more testing

> +	fd = shm_unlink(shm_name);
>  
> -	errno = 0;
> -	err = mlock(mptr, _SC_PAGE_SIZE);
> -	if (err == -1)
> -		fprintf(stderr, "ERROR, mlock %s\n", strerror(errno));
> +	if ((fd == -1) && (errno != ENOENT))
> +		fprintf(stderr, "ERROR: shm_unlink %s\n", strerror(errno));
>  
> -	return err;
> -}
> +	fd = shm_open(shm_name, O_RDWR|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH);
> +	if (fd == -1)
> +		fprintf(stderr, "ERROR: shm_open %s\n", strerror(errno));
>  
> -static void rstat_setup(void)
> -{
> -	int res;
> -	void *mptr = NULL;
> -
> -	int sfd = rstat_shm_open();
> -	if (sfd < 0)
> -		goto rstat_err;
> -
> -	res = rstat_ftruncate(sfd, _SC_PAGE_SIZE);
> -	if (res)
> -		goto rstat_err1;
> -
> -	mptr = rstat_mmap(sfd);
> -	if (mptr == MAP_FAILED)
> -		goto rstat_err1;
> -
> -	res = rstat_mlock(mptr);
> -	if (res)
> -		goto rstat_err2;
> -
> -	return;
> -
> -rstat_err2:
> -	munmap(mptr, _SC_PAGE_SIZE);
> -rstat_err1:
> -	close(sfd);
> -	shm_unlink(shm_name);
> -rstat_err:
> -	rstat_fd = -1;
> -	return;
> +	rstat_fd = fd;
>  }
>  
>  static void write_stats(FILE *f, void *data)
> -- 
> 2.53.0
> 
> 
>