[CRIU] [PATCH 4/4] net: Make sure the entries exist before read them

[Pavel Emelyanov]

On 04/30/2015 11:07 PM, Cyrill Gorcunov wrote:
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  include/net.h |  2 ++
>  net.c         | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net.h b/include/net.h
> index c03105c109bd..c940e15a4021 100644
> --- a/include/net.h
> +++ b/include/net.h
> @@ -30,4 +30,6 @@ extern int restore_link_parms(NetDeviceEntry *nde, int nlsk);
>  extern int veth_pair_add(char *in, char *out);
>  extern int move_veth_to_bridge(void);
>  
> +extern int net_init_devconfs(void);
> +
>  #endif /* __CR_NET_H__ */
> diff --git a/net.c b/net.c
> index fb64d2ebfb62..448de3c1adbe 100644
> --- a/net.c
> +++ b/net.c
> @@ -79,10 +79,47 @@ static char *devconfs[] = {
>  	"shared_media",
>  	"src_valid_mark",
>  	"tag",
> -	NULL,
>  };
>  
> +static int devconfs_status[ARRAY_SIZE(devconfs)] = {
> +	[0 ... (ARRAY_SIZE(devconfs) - 1)] = 1,
> +};
> +
> +/*
> + * I case if some entry is missing in
> + * the kernel, simply write DEVCONFS_UNUSED
> + * into the image so we would skip it.
> + */
> +#define DEVCONFS_UNUSED	(-1u)
> +
>  #define NET_CONF_PATH "net/ipv4/conf"
> +
> +int net_init_devconfs(void)
> +{
> +	static bool inited = false;
> +	size_t i;
> +	int dir;
> +
> +	BUILD_BUG_ON(ARRAY_SIZE(devconfs) != ARRAY_SIZE(devconfs_status));
> +
> +	if (inited)
> +		return 0;
> +
> +	dir = open("/proc/sys/" NET_CONF_PATH "/all", O_RDONLY);
> +	if (dir < 0) {
> +		pr_perror("Can't open sysctl dir");
> +		return -1;
> +	}
> +
> +	for (i = 0; i < ARRAY_SIZE(devconfs); i++) {

Can we, instead of this loop, teach sysctl.c to handle missing entries
itself?

> +		if (faccessat(dir, devconfs[i], F_OK, 0)) {
> +			pr_debug("devconfs: No %s entry\n", devconfs[i]);
> +			devconfs_status[i] = DEVCONFS_UNUSED;
> +		}
> +	}
> +	close(dir);
> +	return 0;
> +}
>  #define MAX_CONF_OPT_PATH IFNAMSIZ+50
>  
>  static int ipv4_conf_op(char *tgt, int *conf, int op, NetnsEntry **netns)
> @@ -101,6 +138,14 @@ static int ipv4_conf_op(char *tgt, int *conf, int op, NetnsEntry **netns)
>  			continue;
>  		}
>  
> +		if (op == CTL_READ && devconfs_status[i] == DEVCONFS_UNUSED) {
> +			conf[i] = DEVCONFS_UNUSED;
> +			continue;
> +		} else {
> +			if (conf[i] == DEVCONFS_UNUSED)
> +				continue;
> +		}
> +
>  		snprintf(path[i], MAX_CONF_OPT_PATH, "%s/%s/%s", NET_CONF_PATH, tgt, devconfs[i]);
>  		req[ri].name = path[i];
>  		req[ri].arg = &conf[i];
> @@ -695,6 +740,9 @@ int dump_net_ns(int ns_id)
>  	if (fds == NULL)
>  		return -1;
>  
> +	if (net_init_devconfs())
> +		return -1;
> +
>  	ret = mount_ns_sysfs();
>  	if (!ret)
>  		ret = dump_netns_conf(fds);
>