[ovs-dev] [PATCHv2] datapath: work around the single GRE receive limitation.

[Gregory Rose]

On 7/11/2018 9:24 AM, William Tu wrote:
> Commit 9f57c67c379d ("gre: Remove support for sharing GRE protocol hook")
> allows only single GRE packet receiver.  When upstream kernel's gre module
> is loaded, the gre.ko exclusively becomes the only gre packet receiver,
> preventing OVS kernel module from registering another gre receiver.
>
> We can either try to unload the gre.ko by removing its dependencies,
> or, in this patch, we try to register OVS as only the GRE transmit
> portion when detecting there already exists another GRE receiver.
>
> Signed-off-by: William Tu <u9012063 at gmail.com>
> Cc: Greg Rose <gvrose8192 at gmail.com>
> Cc: Yifeng Sun <pkusunyifeng at gmail.com>

You can go ahead and add my Tested-by and Reviewed-by tags.

Thanks,

- Greg

> ---
> v1->v2: improve warnning message
> ---
>   datapath/linux/compat/ip_gre.c | 60 +++++++++++++++++++++++++++++++++---------
>   datapath/vport.c               | 12 ++++++---
>   2 files changed, 56 insertions(+), 16 deletions(-)
>
> diff --git a/datapath/linux/compat/ip_gre.c b/datapath/linux/compat/ip_gre.c
> index 92de70127189..1ab798164894 100644
> --- a/datapath/linux/compat/ip_gre.c
> +++ b/datapath/linux/compat/ip_gre.c
> @@ -71,6 +71,7 @@ static void erspan_build_header(struct sk_buff *skb,
>   				bool truncate, bool is_ipv4);
>   
>   static struct rtnl_link_ops ipgre_link_ops __read_mostly;
> +static bool ip_gre_loaded = false;
>   
>   #define ip_gre_calc_hlen rpl_ip_gre_calc_hlen
>   static int ip_gre_calc_hlen(__be16 o_flags)
> @@ -1640,25 +1641,57 @@ int rpl_ipgre_init(void)
>   	int err;
>   
>   	err = register_pernet_device(&ipgre_tap_net_ops);
> -	if (err < 0)
> -		goto pnet_tap_failed;
> +	if (err < 0) {
> +		if (err == -EEXIST)
> +			goto ip_gre_loaded;
> +		else
> +			goto pnet_tap_failed;
> +	}
>   
>   	err = register_pernet_device(&erspan_net_ops);
> -	if (err < 0)
> -		goto pnet_erspan_failed;
> +	if (err < 0) {
> +		if (err == -EEXIST)
> +			goto ip_gre_loaded;
> +		else
> +			goto pnet_erspan_failed;
> +	}
>   
>   	err = register_pernet_device(&ipgre_net_ops);
> -	if (err < 0)
> -		goto pnet_ipgre_failed;
> +	if (err < 0) {
> +		if (err == -EEXIST)
> +			goto ip_gre_loaded;
> +		else
> +			goto pnet_ipgre_failed;
> +	}
>   
>   	err = gre_add_protocol(&ipgre_protocol, GREPROTO_CISCO);
>   	if (err < 0) {
>   		pr_info("%s: can't add protocol\n", __func__);
> -		goto add_proto_failed;
> +		if (err == -EBUSY) {
> +			goto ip_gre_loaded;
> +		} else {
> +			goto add_proto_failed;
> +		}
>   	}
>   
>   	pr_info("GRE over IPv4 tunneling driver\n");
> -	
> +	ovs_vport_ops_register(&ovs_ipgre_vport_ops);
> +	ovs_vport_ops_register(&ovs_erspan_vport_ops);
> +	return 0;
> +
> +ip_gre_loaded:
> +	/* Since GRE only allows single receiver to be registerd,
> +	 * we skip here so only gre transmit works, see:
> +	 *
> +	 * commit 9f57c67c379d88a10e8ad676426fee5ae7341b14
> +	 * Author: Pravin B Shelar <pshelar at nicira.com>
> +	 * Date:   Fri Aug 7 23:51:52 2015 -0700
> +	 *     gre: Remove support for sharing GRE protocol hook
> +	 *
> +	 * OVS GRE receive part is disabled.
> +	 */
> +	pr_info("GRE TX only over IPv4 tunneling driver\n");
> +	ip_gre_loaded = true;
>   	ovs_vport_ops_register(&ovs_ipgre_vport_ops);
>   	ovs_vport_ops_register(&ovs_erspan_vport_ops);
>   	return 0;
> @@ -1678,10 +1711,13 @@ void rpl_ipgre_fini(void)
>   {
>   	ovs_vport_ops_unregister(&ovs_erspan_vport_ops);
>   	ovs_vport_ops_unregister(&ovs_ipgre_vport_ops);
> -	gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
> -	unregister_pernet_device(&ipgre_net_ops);
> -	unregister_pernet_device(&erspan_net_ops);
> -	unregister_pernet_device(&ipgre_tap_net_ops);
> +
> +	if (!ip_gre_loaded) {
> +		gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
> +		unregister_pernet_device(&ipgre_net_ops);
> +		unregister_pernet_device(&erspan_net_ops);
> +		unregister_pernet_device(&ipgre_tap_net_ops);
> +	}
>   }
>   
>   #endif
> diff --git a/datapath/vport.c b/datapath/vport.c
> index 02f6b56d3243..28ddb865c3a2 100644
> --- a/datapath/vport.c
> +++ b/datapath/vport.c
> @@ -66,11 +66,15 @@ int ovs_vport_init(void)
>   	if (err)
>   		goto err_lisp;
>   	err = gre_init();
> -	if (err && err != -EEXIST)
> +	if (err && err != -EEXIST) {
>   		goto err_gre;
> -	else if (err == -EEXIST)
> -		pr_warn("Cannot take GRE protocol entry - The ERSPAN feature may not be supported\n");
> -	else {
> +	} else {
> +		if (err == -EEXIST) {
> +			pr_warn("Cannot take GRE protocol rx entry"\
> +				"- The GRE/ERSPAN rx feature not supported\n");
> +			/* continue GRE tx */
> +		}
> +
>   		err = ipgre_init();
>   		if (err && err != -EEXIST)
>   			goto err_ipgre;