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

[Eric Woudstra <ericwouds@gmail.com>]

On 10/16/24 9:43 AM, Nikolay Aleksandrov wrote:
> 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.

I see, thanks. I'll drop the check in v2.

>>>> +		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);
>>>>  
>>>>  /**
>>>
>