linux-kernel - Re: [PATCH net-next v5 1/5] net: udp: add freebind option to udp_sock

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Message-ID: <aJxaIeUT8wWZRw22@shredder>
Date: Wed, 13 Aug 2025 12:25:53 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Richard Gobert <richardbgobert@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	donald.hunter@...il.com, andrew+netdev@...n.ch, dsahern@...nel.org,
	shuah@...nel.org, daniel@...earbox.net, jacob.e.keller@...el.com,
	razor@...ckwall.org, petrm@...dia.com, menglong8.dong@...il.com,
	martin.lau@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 1/5] net: udp: add freebind option to
 udp_sock_create

On Tue, Aug 12, 2025 at 02:51:51PM +0200, Richard Gobert wrote:
> udp_sock_create creates a UDP socket and binds it according to
> udp_port_cfg.
> 
> Add a freebind option to udp_port_cfg that allows a socket to be bound
> as though IP_FREEBIND is set.
> 
> This change is required for binding vxlan sockets to their local address
> when the outgoing interface is down.

It's not necessarily the outgoing interface, but rather the interface to
which the address is assigned.

Anyway, I'm not sure this change is actually necessary. It was only
added in v4 because back then the default behavior was changed to bind
the VXLAN socket to the local address and existing selftests do not
necessarily configure the address before putting the VXLAN device up.

Given that in this version binding the VXLAN socket to the local address
is opt-in, it seems legitimate to prevent user space from putting the
VXLAN device up if the new option is enabled and the local address is
not present. It can also be documented in the man page so that users are
not surprised.