Re: [PATCH RFC v1 net-next 06/12] net: core: dev: Add dev_fill_bridge_path()

[Nikolay Aleksandrov <razor@blackwall.org>]

On 14/10/2024 21:34, Eric Woudstra wrote:
> 
> 
> On 10/14/24 8:59 AM, Nikolay Aleksandrov wrote:
>> On 13/10/2024 21:55, Eric Woudstra wrote:
>>> New function dev_fill_bridge_path(), similar to dev_fill_forward_path().
>>> It handles starting from a bridge port instead of the bridge master.
>>> The structures ctx and nft_forward_info need to be already filled in with
>>> the (vlan) encaps.
>>>
>>> Signed-off-by: Eric Woudstra <ericwouds@gmail.com>
>>> ---
>>>  include/linux/netdevice.h |  2 +
>>>  net/core/dev.c            | 77 ++++++++++++++++++++++++++++++++-------
>>>  2 files changed, 66 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>> index e87b5e488325..9d80f650345e 100644
>>> --- a/include/linux/netdevice.h
>>> +++ b/include/linux/netdevice.h
>>> @@ -3069,6 +3069,8 @@ void dev_remove_offload(struct packet_offload *po);
>>>  
>>>  int dev_get_iflink(const struct net_device *dev);
>>>  int dev_fill_metadata_dst(struct net_device *dev, struct sk_buff *skb);
>>> +int dev_fill_bridge_path(struct net_device_path_ctx *ctx,
>>> +			 struct net_device_path_stack *stack);
>>>  int dev_fill_forward_path(const struct net_device *dev, const u8 *daddr,
>>>  			  struct net_device_path_stack *stack);
>>>  struct net_device *__dev_get_by_flags(struct net *net, unsigned short flags,
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index cd479f5f22f6..49959c4904fc 100644
>>> --- a/net/core/dev.c
>>> +++ b/net/core/dev.c
>>> @@ -713,44 +713,95 @@ static struct net_device_path *dev_fwd_path(struct net_device_path_stack *stack)
>>>  	return &stack->path[k];
>>>  }
>>>  
>>> -int dev_fill_forward_path(const struct net_device *dev, const u8 *daddr,
>>> -			  struct net_device_path_stack *stack)
>>> +static int dev_fill_forward_path_common(struct net_device_path_ctx *ctx,
>>> +					struct net_device_path_stack *stack)
>>>  {
>>>  	const struct net_device *last_dev;
>>> -	struct net_device_path_ctx ctx = {
>>> -		.dev	= dev,
>>> -	};
>>>  	struct net_device_path *path;
>>>  	int ret = 0;
>>>  
>>> -	memcpy(ctx.daddr, daddr, sizeof(ctx.daddr));
>>> -	stack->num_paths = 0;
>>> -	while (ctx.dev && ctx.dev->netdev_ops->ndo_fill_forward_path) {
>>> -		last_dev = ctx.dev;
>>> +	while (ctx->dev && ctx->dev->netdev_ops->ndo_fill_forward_path) {
>>> +		last_dev = ctx->dev;
>>>  		path = dev_fwd_path(stack);
>>>  		if (!path)
>>>  			return -1;
>>>  
>>>  		memset(path, 0, sizeof(struct net_device_path));
>>> -		ret = ctx.dev->netdev_ops->ndo_fill_forward_path(&ctx, path);
>>> +		ret = ctx->dev->netdev_ops->ndo_fill_forward_path(ctx, path);
>>>  		if (ret < 0)
>>>  			return -1;
>>>  
>>> -		if (WARN_ON_ONCE(last_dev == ctx.dev))
>>> +		if (WARN_ON_ONCE(last_dev == ctx->dev))
>>>  			return -1;
>>>  	}
>>>  
>>> -	if (!ctx.dev)
>>> +	if (!ctx->dev)
>>>  		return ret;
>>>  
>>>  	path = dev_fwd_path(stack);
>>>  	if (!path)
>>>  		return -1;
>>>  	path->type = DEV_PATH_ETHERNET;
>>> -	path->dev = ctx.dev;
>>> +	path->dev = ctx->dev;
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +int dev_fill_bridge_path(struct net_device_path_ctx *ctx,
>>> +			 struct net_device_path_stack *stack)
>>> +{
>>> +	const struct net_device *last_dev, *br_dev;
>>> +	struct net_device_path *path;
>>> +	int ret = 0;
>>> +
>>> +	stack->num_paths = 0;
>>> +
>>> +	if (!ctx->dev || !netif_is_bridge_port(ctx->dev))
>>> +		return -1;
>>> +
>>> +	br_dev = netdev_master_upper_dev_get_rcu((struct net_device *)ctx->dev);
>>> +	if (!br_dev || !br_dev->netdev_ops->ndo_fill_forward_path)
>>> +		return -1;
>>> +
>>> +	last_dev = ctx->dev;
>>> +	path = dev_fwd_path(stack);
>>> +	if (!path)
>>> +		return -1;
>>> +
>>> +	memset(path, 0, sizeof(struct net_device_path));
>>> +	ret = br_dev->netdev_ops->ndo_fill_forward_path(ctx, path);
>>> +	if (ret < 0)
>>> +		return -1;
>>> +
>>> +	if (!ctx->dev || WARN_ON_ONCE(last_dev == ctx->dev))
>>> +		return -1;

* ^^^^^^^^^ here

>>> +
>>> +	if (!netif_is_bridge_master(ctx->dev))
>>
>> hmm, do we expect ctx->dev to be a bridge master? Looking at
>> br_fill_forward_path, it seems to be == fdb->dst->dev which
>> should be the target port
> 
> It would indeed be very unlikely. It was a left-over from code I wrote,
> thinking that here I could handle cascaded bridges (via vlan-device). I
> dropped that, since conntrack does not follow this flow.
> 
> So would it be better to only make sure that ctx->dev is not a bridge
> master?
> 
> 	if (netif_is_bridge_master(ctx->dev))
> 		return -1;
> 
> 	return dev_fill_forward_path_common(ctx, stack);
> 

I think you misunderstood me, I don't think ctx->dev can ever be a bridge
device because ctx->dev gets set to fdb->dst and fdbs that point to the bridge
itself have fdb->dst == NULL but ctx->dev is checked against NULL earlier*
so the bridge dev check doesn't make sense to me.

>>> +		return dev_fill_forward_path_common(ctx, stack);
>>> +
>>> +	path = dev_fwd_path(stack);
>>> +	if (!path)
>>> +		return -1;
>>> +	path->type = DEV_PATH_ETHERNET;
>>> +	path->dev = ctx->dev;
>>>  
>>>  	return ret;
>>>  }
>>> +EXPORT_SYMBOL_GPL(dev_fill_bridge_path);
>>> +
>>> +int dev_fill_forward_path(const struct net_device *dev, const u8 *daddr,
>>> +			  struct net_device_path_stack *stack)
>>> +{
>>> +	struct net_device_path_ctx ctx = {
>>> +		.dev	= dev,
>>> +	};
>>> +
>>> +	memcpy(ctx.daddr, daddr, sizeof(ctx.daddr));
>>> +
>>> +	stack->num_paths = 0;
>>> +
>>> +	return dev_fill_forward_path_common(&ctx, stack);
>>> +}
>>>  EXPORT_SYMBOL_GPL(dev_fill_forward_path);
>>>  
>>>  /**
>>