[lxc-devel] [PATCH 1/1] lxc-user-nic: compute first available nic name in container

[Stéphane Graber]

On Mon, Jul 21, 2014 at 07:27:02PM +0000, Serge Hallyn wrote:
> Rather than always using eth0.  Otherwise unpriv containers cannot have
> multiple lxc.network.type = veth's without manually setting
> lxc.network.name =.
> 
> Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> ---
>  src/lxc/lxc_user_nic.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
> 
> diff --git a/src/lxc/lxc_user_nic.c b/src/lxc/lxc_user_nic.c
> index 1105b3d..75e4851 100644
> --- a/src/lxc/lxc_user_nic.c
> +++ b/src/lxc/lxc_user_nic.c
> @@ -470,7 +470,7 @@ again:
>  	goto again;
>  }
>  
> -static int rename_in_ns(int pid, char *oldname, char *newname)
> +static int rename_in_ns(int pid, char *oldname, char **newnamep)
>  {
>  	char nspath[MAXPATHLEN];
>  	int fd = -1, ofd = -1, ret;
> @@ -495,8 +495,29 @@ static int rename_in_ns(int pid, char *oldname, char *newname)
>  		goto out_err;
>  	}
>  	close(fd); fd = -1;
> -	if ((ret = lxc_netdev_rename_by_name(oldname, newname)) < 0) {
> -		fprintf(stderr, "Error %d renaming netdev %s to %s in container\n", ret, oldname, newname);
> +
> +	if (!*newnamep) {
> +		int i = 0;
> +		char nicname[10];
> +		while (i < 100) {
> +			ret = snprintf(nicname, 10, "eth%d", i);
> +			if (ret < 0 || ret >= 10)
> +				return -1;
> +			if (if_nametoindex(nicname) == 0)
> +				break;
> +			i++;
> +		}
> +		if (i == 100) {
> +			fprintf(stderr, "too many nics in container\n");
> +			return -1;
> +		}
> +		*newnamep = strdup(nicname);
> +		if (!*newnamep)
> +			return -1;
> +	}

As I said on IRC, are you sure we can't somehow get rid of all of that
code and just somehow pass 'eth%d' to the kernel through netlink which
will then make it use the next available ethX device (we already use
that trick for privileged networking).

> +
> +	if ((ret = lxc_netdev_rename_by_name(oldname, *newnamep)) < 0) {
> +		fprintf(stderr, "Error %d renaming netdev %s to %s in container\n", ret, oldname, *newnamep);
>  		goto out_err;
>  	}
>  	if (setns(ofd, 0) < 0) {
> @@ -579,7 +600,7 @@ int main(int argc, char *argv[])
>  	if (argc >= 5)
>  		vethname = argv[4];
>  	else
> -		vethname = "eth0";
> +		vethname = NULL;
>  
>  	errno = 0;
>  	pid = (int) strtol(argv[1], NULL, 10);
> @@ -614,7 +635,7 @@ int main(int argc, char *argv[])
>  	}
>  
>  	// Now rename the link
> -	if (rename_in_ns(pid, cnic, vethname) < 0) {
> +	if (rename_in_ns(pid, cnic, &vethname) < 0) {
>  		fprintf(stderr, "Failed to rename the link\n");
>  		exit(1);
>  	}
> -- 
> 1.9.1
> 
> _______________________________________________
> lxc-devel mailing list
> lxc-devel at lists.linuxcontainers.org
> http://lists.linuxcontainers.org/listinfo/lxc-devel

-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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