Subject: Re: [PATCH net-next 1/3] mpls: move mpls_route nexthop fields to a new nhlfe struct

From: Robert Shearman <[email-masked]>
Date: Wed, 12 Aug 2015 20:15:07 +0100

On 11/08/15 22:45, Roopa Prabhu wrote:
> From: Roopa Prabhu <[email-masked]>
>
> moves mpls_route nexthop fields to a new mpls_nhlfe
> struct. mpls_nhlfe represents a mpls nexthop label forwarding entry.
> It prepares mpls route structure for multipath support.
>
> In the process moves mpls_route structure into internal.h.

Is there a requirement for moving this and the new datastructures into 
internal.h? I may have missed it, but I don't see any dependency on this 
in this patch series.

> Moves some of the code from mpls_route_add into a separate mpls
> nhlfe build function. changed mpls_rt_alloc to take number of
> nexthops as argument.
>
> A mpls route can point to multiple mpls_nhlfe. This patch
> does not support multipath yet, hence the rest of the changes
> assume that a mpls route points to a single mpls_nhlfe
>
> Signed-off-by: Roopa Prabhu <[email-masked]>
> ---
>   net/mpls/af_mpls.c  |  225 ++++++++++++++++++++++++++++-----------------------
>   net/mpls/internal.h |   35 ++++++++
>   2 files changed, 158 insertions(+), 102 deletions(-)
>
> diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
> index 8c5707d..cf86e9d 100644
> --- a/net/mpls/af_mpls.c
> +++ b/net/mpls/af_mpls.c
> @@ -21,35 +21,6 @@
>   #endif
>   #include "internal.h"
>
> -#define LABEL_NOT_SPECIFIED (1<<20)
> -#define MAX_NEW_LABELS 2
> -
> -/* This maximum ha length copied from the definition of struct neighbour */
> -#define MAX_VIA_ALEN (ALIGN(MAX_ADDR_LEN, sizeof(unsigned long)))
> -
> -enum mpls_payload_type {
> -	MPT_UNSPEC, /* IPv4 or IPv6 */
> -	MPT_IPV4 = 4,
> -	MPT_IPV6 = 6,
> -
> -	/* Other types not implemented:
> -	 *  - Pseudo-wire with or without control word (RFC4385)
> -	 *  - GAL (RFC5586)
> -	 */
> -};
> -
> -struct mpls_route { /* next hop label forwarding entry */
> -	struct net_device __rcu *rt_dev;
> -	struct rcu_head		rt_rcu;
> -	u32			rt_label[MAX_NEW_LABELS];
> -	u8			rt_protocol; /* routing protocol that set this entry */
> -	u8                      rt_payload_type;
> -	u8			rt_labels;
> -	u8			rt_via_alen;
> -	u8			rt_via_table;
> -	u8			rt_via[0];
> -};
> -
>   static int zero = 0;
>   static int label_limit = (1 << 20) - 1;
>
...
> @@ -281,13 +254,15 @@ struct mpls_route_config {
>   	struct nl_info		rc_nlinfo;
>   };
>
> -static struct mpls_route *mpls_rt_alloc(size_t alen)
> +static struct mpls_route *mpls_rt_alloc(int num_nh)
>   {
>   	struct mpls_route *rt;
>
> -	rt = kzalloc(sizeof(*rt) + alen, GFP_KERNEL);
> +	rt = kzalloc(sizeof(*rt) + (num_nh * sizeof(struct mpls_nhlfe)),

How about this instead:
   offsetof(typeof(*rt), rt_nh[num_nh])
?

That way, you don't need to write out the type of rt_nh here.

> +		     GFP_KERNEL);
>   	if (rt)
> -		rt->rt_via_alen = alen;
> +		rt->rt_nhn = num_nh;
> +
>   	return rt;
>   }
>
> @@ -322,7 +297,7 @@ static void mpls_route_update(struct net *net, unsigned index,
>
>   	platform_label = rtnl_dereference(net->mpls.platform_label);
>   	rt = rtnl_dereference(platform_label[index]);
> -	if (!dev || (rt && (rtnl_dereference(rt->rt_dev) == dev))) {
> +	if (!dev || (rt && (rtnl_dereference(rt->rt_nh->nh_dev) == dev))) {
>   		rcu_assign_pointer(platform_label[index], new);
>   		old = rt;
>   	}
> @@ -406,23 +381,23 @@ static struct net_device *inet6_fib_lookup_dev(struct net *net, void *addr)
>   #endif
>
>   static struct net_device *find_outdev(struct net *net,
> -				      struct mpls_route_config *cfg)
> +				      struct mpls_nhlfe *nhlfe, int oif)
>   {
>   	struct net_device *dev = NULL;
>
> -	if (!cfg->rc_ifindex) {
> -		switch (cfg->rc_via_table) {
> +	if (!oif) {
> +		switch (nhlfe->nh_via_table) {
>   		case NEIGH_ARP_TABLE:
> -			dev = inet_fib_lookup_dev(net, cfg->rc_via);
> +			dev = inet_fib_lookup_dev(net, nhlfe->nh_via);
>   			break;
>   		case NEIGH_ND_TABLE:
> -			dev = inet6_fib_lookup_dev(net, cfg->rc_via);
> +			dev = inet6_fib_lookup_dev(net, nhlfe->nh_via);
>   			break;
>   		case NEIGH_LINK_TABLE:
>   			break;
>   		}
>   	} else {
> -		dev = dev_get_by_index(net, cfg->rc_ifindex);
> +		dev = dev_get_by_index(net, oif);
>   	}
>
>   	if (!dev)
> @@ -431,15 +406,81 @@ static struct net_device *find_outdev(struct net *net,
>   	return dev;
>   }
>
> +int mpls_nhlfe_assign_dev(struct net *net, struct mpls_nhlfe *nhlfe, int oif)
> +{
> +	struct net_device *dev = NULL;
> +	int err = -ENODEV;
> +
> +	dev = find_outdev(net, nhlfe, oif);
> +	if (IS_ERR(dev)) {
> +		err = PTR_ERR(dev);
> +		dev = NULL;
> +		goto errout;
> +	}
> +
> +	/* Ensure this is a supported device */
> +	err = -EINVAL;
> +	if (!mpls_dev_get(dev))
> +		goto errout;
> +
> +	/* For now just support ethernet devices */
> +	err = -EINVAL;
> +	if ((dev->type != ARPHRD_ETHER) && (dev->type != ARPHRD_LOOPBACK))
> +		goto errout;

Isn't this interface type check redundant with the mpls_dev_get call 
just above?

> +
> +	RCU_INIT_POINTER(nhlfe->nh_dev, dev);
> +	dev_put(dev);

Is it safe to release the reference to dev here? Prior to these changes, 
it was released after mpls_route_update is called in mpls_route_add - is 
that OK without a reference?

> +
> +	return 0;
> +
> +errout:
> +	if (dev)
> +		dev_put(dev);
> +	return err;
> +}
> +
> +static int mpls_nhlfe_build(struct mpls_route_config *cfg,
> +			    struct mpls_nhlfe *nhlfe)
> +{
> +	struct net *net = cfg->rc_nlinfo.nl_net;
> +	int err = -ENOMEM;
> +	int i;
> +
> +	if (!nhlfe)
> +		goto errout;
> +
> +	err = -EINVAL;
> +	/* Ensure only a supported number of labels are present */
> +	if (cfg->rc_output_labels > MAX_NEW_LABELS)
> +		goto errout;
> +
> +	nhlfe->nh_labels = cfg->rc_output_labels;
> +	for (i = 0; i < nhlfe->nh_labels; i++)
> +		nhlfe->nh_label[i] = cfg->rc_output_label[i];
> +
> +	nhlfe->nh_payload_type = cfg->rc_payload_type;
> +	nhlfe->nh_via_table = cfg->rc_via_table;
> +	memcpy(nhlfe->nh_via, cfg->rc_via, cfg->rc_via_alen);
> +	nhlfe->nh_via_alen = cfg->rc_via_alen;

Shouldn't this check that was removed from mpls_route_add be added here:

-	if ((cfg->rc_via_table == NEIGH_LINK_TABLE) &&
-	    (dev->addr_len != cfg->rc_via_alen))
-		goto errout;

?

> +
> +	err = mpls_nhlfe_assign_dev(net, nhlfe, cfg->rc_ifindex);
> +	if (err)
> +		goto errout;
> +
> +	return 0;
> +
> +errout:
> +	return err;
> +}
> +
>   static int mpls_route_add(struct mpls_route_config *cfg)
>   {
>   	struct mpls_route __rcu **platform_label;
>   	struct net *net = cfg->rc_nlinfo.nl_net;
> -	struct net_device *dev = NULL;
>   	struct mpls_route *rt, *old;
> -	unsigned index;
> -	int i;
>   	int err = -EINVAL;
> +	unsigned index;
> +	int nhs = 1; /* default to one nexthop */
>
>   	index = cfg->rc_label;
>
> @@ -457,27 +498,6 @@ static int mpls_route_add(struct mpls_route_config *cfg)
>   	if (index >= net->mpls.platform_labels)
>   		goto errout;
>
> -	/* Ensure only a supported number of labels are present */
> -	if (cfg->rc_output_labels > MAX_NEW_LABELS)
> -		goto errout;
> -
> -	dev = find_outdev(net, cfg);
> -	if (IS_ERR(dev)) {
> -		err = PTR_ERR(dev);
> -		dev = NULL;
> -		goto errout;
> -	}
> -
> -	/* Ensure this is a supported device */
> -	err = -EINVAL;
> -	if (!mpls_dev_get(dev))
> -		goto errout;
> -
> -	err = -EINVAL;
> -	if ((cfg->rc_via_table == NEIGH_LINK_TABLE) &&
> -	    (dev->addr_len != cfg->rc_via_alen))
> -		goto errout;
> -
>   	/* Append makes no sense with mpls */
>   	err = -EOPNOTSUPP;
>   	if (cfg->rc_nlflags & NLM_F_APPEND)
...
> diff --git a/net/mpls/internal.h b/net/mpls/internal.h
> index 2681a4b..f05e2e8 100644
> --- a/net/mpls/internal.h
> +++ b/net/mpls/internal.h
...
> @@ -21,6 +32,30 @@ struct mpls_dev {
>
>   struct sk_buff;
>
> +#define LABEL_NOT_SPECIFIED (1 << 20)
> +#define MAX_NEW_LABELS 2
> +
> +/* This maximum ha length copied from the definition of struct neighbour */
> +#define MAX_VIA_ALEN (ALIGN(MAX_ADDR_LEN, sizeof(unsigned long)))
> +
> +struct mpls_nhlfe { /* next hop label forwarding entry */

Can we just call this mpls_nh? IMHO, NHLFE is a bit of MPLS-specific 
jargon that doesn't really add anything and may impact readability for 
anybody familiar with other protocols, but not with the MPLS RFCs.

> +	struct net_device __rcu *nh_dev;
> +	u32			nh_label[MAX_NEW_LABELS];
> +	unsigned int		nh_flags;

Is it worth adding the nh_flags field? Unless I missed something it 
isn't used in this patch and isn't written in any subsequent patches.

> +	u8			nh_payload_type;

nh_payload_type isn't really an attribute of the nexthop, but of the 
route - it's signally the type of traffic that is using that route.

> +	u8			nh_labels;
> +	u8			nh_via_alen;
> +	u8			nh_via_table;
> +	u8			nh_via[MAX_VIA_ALEN];

MAX_VIA_ALEN is 32 bytes, so there is now a 28 byte overhead per nexthop 
for the common case of using an IPv4 nexthop. With a large number of 
routes/nexthops, this will become noticeable. If we avoided using a 
fixed allocation, it would mitigate this.

> +};
> +
> +struct mpls_route { /* next hop label forwarding entry */

Is it still the NHLFE? :-)

> +	struct rcu_head		rt_rcu;
> +	u8			rt_protocol;
> +	int			rt_nhn;
> +	struct mpls_nhlfe	rt_nh[0];
> +};
> +
>   static inline struct mpls_shim_hdr *mpls_hdr(const struct sk_buff *skb)
>   {
>   	return (struct mpls_shim_hdr *)skb_network_header(skb);
>

Thanks,
Rob