[LTP] [PATCH] unshare03: using soft limit of NOFILE

[Cyril Hrubis]

Hi!
> I think it's safer to set NOFILE increasing from soft limit than from
> hard limit.
> 
> Hard limit may lead to dup2 ENOMEM error which bring the result to
> TBROK on little memory machine. (e.g. 2GB memory in my situation, hard
> limit in /proc/sys/fs/nr_open come out to be 1073741816)
> 
> Signed-off-by: lufei <lufei@uniontech.com>
> ---
>  testcases/kernel/syscalls/unshare/unshare03.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/testcases/kernel/syscalls/unshare/unshare03.c b/testcases/kernel/syscalls/unshare/unshare03.c
> index 7c5e71c4e..bb568264c 100644
> --- a/testcases/kernel/syscalls/unshare/unshare03.c
> +++ b/testcases/kernel/syscalls/unshare/unshare03.c
> @@ -24,7 +24,7 @@
>  
>  static void run(void)
>  {
> -	int nr_open;
> +	int rlim_max;
>  	int nr_limit;
>  	struct rlimit rlimit;
>  	struct tst_clone_args args = {
> @@ -32,14 +32,12 @@ static void run(void)
>  		.exit_signal = SIGCHLD,
>  	};
>  
> -	SAFE_FILE_SCANF(FS_NR_OPEN, "%d", &nr_open);
> -	tst_res(TDEBUG, "Maximum number of file descriptors: %d", nr_open);
> +	SAFE_GETRLIMIT(RLIMIT_NOFILE, &rlimit);
> +	rlim_max = rlimit.rlim_max;
>  
> -	nr_limit = nr_open + NR_OPEN_LIMIT;
> +	nr_limit = rlim_max + NR_OPEN_LIMIT;
>  	SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", nr_limit);
>  
> -	SAFE_GETRLIMIT(RLIMIT_NOFILE, &rlimit);
> -
>  	rlimit.rlim_cur = nr_limit;
>  	rlimit.rlim_max = nr_limit;
>  
> @@ -47,10 +45,10 @@ static void run(void)
>  	tst_res(TDEBUG, "Set new maximum number of file descriptors to : %d",
>  		nr_limit);
>  
> -	SAFE_DUP2(2, nr_open + NR_OPEN_DUP);
> +	SAFE_DUP2(2, rlim_max + NR_OPEN_DUP);
>  
>  	if (!SAFE_CLONE(&args)) {
> -		SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", nr_open);
> +		SAFE_FILE_PRINTF(FS_NR_OPEN, "%d", rlim_max);
>  		TST_EXP_FAIL(unshare(CLONE_FILES), EMFILE);
>  		exit(0);
>  	}

Why do we bother with reading the /rpoc/sys/fs/nr_open file? All that we
need to to do is to dup() a file descriptor and tnen set the nr_open
limit to fd - 2. And if we do so we can drop the rlimit that increases
the limit so that it's greater than nr_open as well.

-- 
Cyril Hrubis
chrubis@suse.cz