On 12/02/2022 11:58, Christophe JAILLET wrote:
> ether_addr_equal_64bits() can easy be used in place of ether_addr_equal()
> here.
> Padding in the 'net_bridge_port' structure is already there because it is a
> huge structure and the required fields are not at the end.
> 'oldaddr' is local to the function. So add the required padding
> explicitly and simplify its definition.
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
> This patch is more a POC for me.
>
> I'm unsure that using ether_addr_equal_64bits() is really useful. The
> speedup should be mostly un-noticeable.
>
> To make sure that we have the required padding, we either need to waste
> some space or rely on the fact that the address is embedded in a large
> enough structure. (which is the case here)
>
> So, it looks fragile to me and not future-proof.
>
> Feed-back highly appreciated to see if such patches are welcome and if I
> should spend some time on it.
> ---
This is slow path, more so as you've noted above the change is fragile and someone
can easily miss it, I appreciate the comments but for this case I'd prefer to
leave the code as-is to keep it obviously correct and avoid future problems.
Thanks,
Nik
> net/bridge/br_private.h | 5 +++++
> net/bridge/br_stp_if.c | 12 +++++++-----
> 2 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 2661dda1a92b..2f78090574c9 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -363,6 +363,11 @@ struct net_bridge_port {
> unsigned char config_pending;
> port_id port_id;
> port_id designated_port;
> + /*
> + * designated_root and designated_bridge must NOT be at the end of the
> + * structure because ether_addr_equal_64bits() requires 2 bytes of
> + * padding.
> + */
> bridge_id designated_root;
> bridge_id designated_bridge;
> u32 path_cost;
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 75204d36d7f9..1bf0aaf29e5e 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -221,9 +221,11 @@ int br_stp_set_enabled(struct net_bridge *br, unsigned long val,
> /* called under bridge lock */
> void br_stp_change_bridge_id(struct net_bridge *br, const unsigned char *addr)
> {
> - /* should be aligned on 2 bytes for ether_addr_equal() */
> - unsigned short oldaddr_aligned[ETH_ALEN >> 1];
> - unsigned char *oldaddr = (unsigned char *)oldaddr_aligned;
> + /*
> + * should be aligned on 2 bytes and have 2 bytes of padding for
> + * ether_addr_equal_64bits()
> + */
> + unsigned char oldaddr[ETH_ALEN + 2] __aligned(2);
> struct net_bridge_port *p;
> int wasroot;
>
> @@ -236,10 +238,10 @@ void br_stp_change_bridge_id(struct net_bridge *br, const unsigned char *addr)
> eth_hw_addr_set(br->dev, addr);
>
> list_for_each_entry(p, &br->port_list, list) {
> - if (ether_addr_equal(p->designated_bridge.addr, oldaddr))
> + if (ether_addr_equal_64bits(p->designated_bridge.addr, oldaddr))
> memcpy(p->designated_bridge.addr, addr, ETH_ALEN);
>
> - if (ether_addr_equal(p->designated_root.addr, oldaddr))
> + if (ether_addr_equal_64bits(p->designated_root.addr, oldaddr))
> memcpy(p->designated_root.addr, addr, ETH_ALEN);
> }
>
