Re: [PATCH v3 3/3] batman-adv: bcast: remove remaining skb-copy calls for broadcasts

[Sven Eckelmann <sven@narfation.org>]

[-- Attachment #1: Type: text/plain, Size: 1217 bytes --]

On Monday, 17 May 2021 00:33:09 CEST Linus Lüssing wrote:
> +       /* __batadv_forw_bcast_packet clones, make sure original
> +        * skb stays writeable
> +        */
> +       return (skb_cow(skb, 0) < 0) ? NETDEV_TX_BUSY : NETDEV_TX_OK;

Just because we had this discussion a couple of hours ago: My last comment 
from May was that the skb_cow might be unnecessary - not that you need a 
skb_copy.

You wrote (for situation B):

> a packet is
> additionally decapsulated and is sent up the stack through
> batadv_recv_bcast_packet()->batadv_interface_rx(). Which needs an
> unshared skb data for potential modifications from other protocols.

And my reply to this was:

> Take for example the bridge code. You can find the skb_share_check in 
> br_handle_frame. Afterwards, it knows that it has a clone of the skb (but not 
> necessarily a private copy of the actual data). If it needs to modify the data 
> then it is copying the skb.
> 
> Another example is the IPv4 code. One of the first things it does is to check 
> in ip_rcv_core for the shared skb. And if it needs to modify it (for example 
> by forwarding it in ip_forward), it uses skb_cow directly.

Kind regards,
	Sven

[-- Attachment #2: This is a digitally signed message part. --]
[-- Type: application/pgp-signature, Size: 833 bytes --]