[CRIU] [PATCH] zdtm: fallback to mknod(/dev/ptmx) when CONFIG_DEVPTS_MULTIPLE_INSTANCES is not set

[Andrew Vagin]

On Tue, Aug 26, 2014 at 05:30:57PM -0700, Filipe Brandenburger wrote:
> A kernel without that option configured does not have /dev/pts/ptmx, so
> fallback to the previous way of creating it using mknod instead.
> 
> The previous code was trying to bind mount ptmx on top of a symlink, which does
> not actually work... Keep only the symlink call and use a relative symlink
> instead. Adjust the error message of the symlink case to mention symlink()
> instead of mknod() and also /dev/ptmx instead of /dev/pts.
> 
> Tested:
> - zdtm test suite runs on ^ns/static/.* before and after the change.
> - Same on a kernel with CONFIG_DEVPTS_MULTIPLE_INSTANCES unset.
> 
> Signed-off-by: Filipe Brandenburger <filbranden at google.com>

Acked-by: Andrew Vagin <avagin at openvz.org>

Thanks.

> ---
>  test/zdtm/lib/ns.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/test/zdtm/lib/ns.c b/test/zdtm/lib/ns.c
> index 8afec5bdf0a5..40e7005d7af3 100644
> --- a/test/zdtm/lib/ns.c
> +++ b/test/zdtm/lib/ns.c
> @@ -72,18 +72,27 @@ static int prepare_mntns()
>  			fprintf(stderr, "mkdir(/dev/pts) failed: %m\n");
>  			return -1;
>  		}
> -		if (symlink("/dev/pts/ptmx", "/dev/ptmx") && errno != EEXIST) {
> -			fprintf(stderr, "mknod(/dev/ptmx) failed: %m\n");
> -			return -1;
> -		}
> -		chmod("/dev/ptmx", 0666);
>  		if (mount("pts", "/dev/pts", "devpts", MS_MGC_VAL, "mode=666,ptmxmode=666,newinstance")) {

It's strange, that mount with newinstance doesn't fail, if
CONFIG_DEVPTS_MULTIPLE_INSTANCES

>  			fprintf(stderr, "mount(/dev/pts) failed: %m\n");
>  			return -1;
>  		}
> -		if (mount("/dev/pts/ptmx", "/dev/ptmx", NULL, MS_BIND, NULL)) {
> -			fprintf(stderr, "mount(/dev/pts) failed: %m\n");
> -			return -1;
> +		/*
> +		 * If CONFIG_DEVPTS_MULTIPLE_INSTANCES=n, then /dev/pts/ptmx
> +		 * does not exist. Fall back to creating the device with
> +		 * mknod() in that case.
> +		 */
> +		if (access("/dev/pts/ptmx", F_OK) == 0) {
> +			if (symlink("pts/ptmx", "/dev/ptmx") && errno != EEXIST) {
> +				fprintf(stderr, "symlink(/dev/ptmx) failed: %m\n");
> +				return -1;
> +			}
> +		} else {
> +			if (mknod("/dev/ptmx", 0666 | S_IFCHR, makedev(5, 2)) == 0) {
> +				chmod("/dev/ptmx", 0666);
> +			} else if (errno != EEXIST) {
> +				fprintf(stderr, "mknod(/dev/ptmx) failed: %m\n");
> +				return -1;
> +			}
>  		}
>  		if (fchdir(dfd)) {
>  			fprintf(stderr, "fchdir() failed: %m\n");
> -- 
> 1.9.3
>