On 2023/10/09 3:39, Willem de Bruijn wrote:
On Sun, Oct 8, 2023 at 7:22 AM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:tun_vnet_hash can use this flag to indicate it stored virtio-net hash cache to cb. Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> --- include/linux/skbuff.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 4174c4b82d13..e638f157c13c 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -837,6 +837,7 @@ typedef unsigned char *sk_buff_data_t; * @truesize: Buffer size * @users: User count - see {datagram,tcp}.c * @extensions: allocated extensions, valid if active_extensions is nonzero + * @tun_vnet_hash: tun stored virtio-net hash cache to cb */ struct sk_buff { @@ -989,6 +990,7 @@ struct sk_buff { #if IS_ENABLED(CONFIG_IP_SCTP) __u8 csum_not_inet:1; #endif + __u8 tun_vnet_hash:1;sk_buff space is very limited. No need to extend it, especially for code that stays within a single subsystem (tun). To a lesser extent the same point applies to the qdisc_skb_cb.
I had to extend sk_buff because it does not stay in tun but moves back and forth between qdisc and tun.
The new members of sk_buff and qdisc_skb_cb are stored by tun's ndo_select_queue(). The control will go back to qdisc after ndo_select_queue() function finishes. Eventually tun's ndo_start_xmit() will be called by qdisc and consumes the stored members. qdisc is required to keep the stored members intact.
tun_vnet_hash is a bit special. It is put into sk_buff because ndo_select_queue() is not always called and it may be left uninitialized. ndo_start_xmit() may read some garbage from cb's old user if it is put into cb.
