linux-kernel - Re: [PATCH net-next v02 1/2] af_packet: allow fanout

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Message-ID: <67054127bb083_18b21e2943f@willemb.c.googlers.com.notmuch>
Date: Tue, 08 Oct 2024 10:26:47 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Gur Stavi <gur.stavi@...wei.com>, 
 Gur Stavi <gur.stavi@...wei.com>
Cc: netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Shuah Khan <shuah@...nel.org>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v02 1/2] af_packet: allow fanout_add when socket
 is not RUNNING

Gur Stavi wrote:
> PACKET socket can retain its fanout membership through link down and up
> and leave a fanout while closed regardless of link state.
> However, socket was forbidden from joining a fanout while it was not
> RUNNING.
> 
> This patch allows PACKET socket to join fanout while not RUNNING.
> 
> Signed-off-by: Gur Stavi <gur.stavi@...wei.com>
> ---
>  net/packet/af_packet.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index f8942062f776..fb2cca73d953 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1846,21 +1846,21 @@ static int fanout_add(struct sock *sk, struct fanout_args *args)
>  	err = -EINVAL;
>  
>  	spin_lock(&po->bind_lock);
> -	if (packet_sock_flag(po, PACKET_SOCK_RUNNING) &&
> -	    match->type == type &&
> +	if (match->type == type &&
>  	    match->prot_hook.type == po->prot_hook.type &&
>  	    match->prot_hook.dev == po->prot_hook.dev) {

Remaining unaddressed issue is that the socket can now be added
before being bound. See comment in v1.

>  		err = -ENOSPC;
>  		if (refcount_read(&match->sk_ref) < match->max_num_members) {
> -			__dev_remove_pack(&po->prot_hook);
> -
>  			/* Paired with packet_setsockopt(PACKET_FANOUT_DATA) */
>  			WRITE_ONCE(po->fanout, match);
>  
>  			po->rollover = rollover;
>  			rollover = NULL;
>  			refcount_set(&match->sk_ref, refcount_read(&match->sk_ref) + 1);
> -			__fanout_link(sk, po);
> +			if (packet_sock_flag(po, PACKET_SOCK_RUNNING)) {
> +				__dev_remove_pack(&po->prot_hook);
> +				__fanout_link(sk, po);
> +			}
>  			err = 0;
>  		}
>  	}
> -- 
> 2.45.2
>