[Virtio-fs] [PATCH] virtiofsd: simplify setup_remount_slave

[Liu Bo]

On Wed, Aug 14, 2019 at 10:27:51AM +0800, Peng Tao wrote:
> We can just use MS_REC to propagate MS_SLAVE. This would also allow us
> to close a race window between reading proc mountinfo and calling
> mount(MS_SLAVE) for each entry, vs. others umounting the mount point in
> parallel.
>

Reviewed-by: Liu Bo <bo.liu at linux.alibaba.com>

thanks,
-liubo

> Signed-off-by: Peng Tao <tao.peng at linux.alibaba.com>
> ---
>  contrib/virtiofsd/passthrough_ll.c | 53 ++----------------------------
>  1 file changed, 3 insertions(+), 50 deletions(-)
> 
> diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
> index 6662cc237a..d1ce369071 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -2032,55 +2032,6 @@ static struct fuse_lowlevel_ops lo_oper = {
>          .removemapping  = lo_removemapping,
>  };
>  
> -/* Remount with MS_SLAVE so our mounts don't affect the outside world */
> -static void setup_remount_slave(void)
> -{
> -	gchar *mountinfo = NULL;
> -	gchar *line;
> -	gchar *nextline;
> -
> -	if (!g_file_get_contents("/proc/self/mountinfo", &mountinfo, NULL, NULL)) {
> -		fprintf(stderr, "unable to read /proc/self/mountinfo\n");
> -		exit(EXIT_FAILURE);
> -	}
> -
> -	for (line = mountinfo; line; line = nextline) {
> -		gchar **fields = NULL;
> -		char *eol;
> -
> -		nextline = NULL;
> -
> -		eol = strchr(line, '\n');
> -		if (eol) {
> -			*eol = '\0';
> -			nextline = eol + 1;
> -		}
> -
> -		/*
> -		 * The line format is:
> -		 * 442 441 253:4 / / rw,relatime shared:1 - xfs /dev/sda1 rw
> -		 */
> -		fields = g_strsplit(line, " ", -1);
> -		if (!fields[0] || !fields[1] || !fields[2] || !fields[3] ||
> -		    !fields[4] || !fields[5] || !fields[6]) {
> -			goto next; /* parsing failed, skip line */
> -		}
> -
> -		if (!strstr(fields[6], "shared")) {
> -			goto next; /* not shared, skip line */
> -		}
> -
> -		if (mount(NULL, fields[4], NULL, MS_SLAVE, NULL) < 0) {
> -			err(1, "mount(%s, MS_SLAVE)", fields[4]);
> -		}
> -
> -next:
> -		g_strfreev(fields);
> -	}
> -
> -	g_free(mountinfo);
> -}
> -
>  /* This magic is based on lxc's lxc_pivot_root() */
>  static void setup_pivot_root(const char *source)
>  {
> @@ -2135,7 +2086,9 @@ static void setup_mount_namespace(const char *source)
>  		err(1, "unshare(CLONE_NEWNS)");
>  	}
>  
> -	setup_remount_slave();
> +	if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
> +		err(1, "mount(/, MS_REC|MS_PRIVATE)");
> +	}
>  
>  	if (mount(source, source, NULL, MS_BIND, NULL) < 0) {
>  		err(1, "mount(%s, %s, MS_BIND)", source, source);
> -- 
> 2.17.1