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Message-ID: <2cc53d1b-2e16-803f-f528-6b94a812d2d7@hartkopp.net>
Date: Thu, 12 May 2022 18:54:46 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Oleksij Rempel <o.rempel@...gutronix.de>,
Wolfgang Grandegger <wg@...ndegger.com>,
Marc Kleine-Budde <mkl@...gutronix.de>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>
Cc: Devid Antonio Filoni <devid.filoni@...uetechnologies.com>,
kernel@...gutronix.de, linux-can@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
David Jander <david@...tonic.nl>
Subject: Re: [PATCH v2] can: skb: add extended skb support
Hi Oleksij,
On 12.05.22 14:59, Oleksij Rempel wrote:
> Add CAN specific skb extension support and add first currently needed
> local_origin variable.
>
> On the CAN stack we push same skb data in different direction depending
> on the interface type:
> - to the HW egress and at same time back to the stack as echo
> - over virtual vcan/vxcan interfaces as egress on one side and ingress on other
> side of the vxcan tunnel.
> We can't use skb->sk as marker of the origin, because not all packets
> not all packets with local_origin are assigned to some socket. Some of
> them are generate from the kernel, for example like J1939 control messages.
> So, to properly detect flow direction is is better to store this information
> as part of the SKB.
>
> The advantage of using skb_ext is that it is options and extendable
> without affecting other skb users. It can be shared between cloned skbs and
> duplicated only if needed.
>
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> Cc: Devid Antonio Filoni <devid.filoni@...uetechnologies.com>
> ---
> changes v2:
> - migrate it to SKB_EXT
The use of SKB_EXT seems to be very costly to just store a boolean value.
What I could see from some of the other SKB_EXT users this extension
(which performs alloc & COW) is used in special circumstances.
With your suggestion this additional effort is needed for every CAN
related skb.
So at least for this use-case extending struct can_skb_priv seems to be
more efficient.
https://elixir.bootlin.com/linux/latest/source/include/linux/can/skb.h#L44
We might get into problems with PF_PACKET sockets when extending the
can_skb_priv length beyond HH_DATA_MOD, see:
https://elixir.bootlin.com/linux/latest/source/include/linux/can/skb.h#L99
But for now I'm not sure that SKB_EXT isn't too heavy to store that
single flag.
Best regards,
Oliver
>
> drivers/net/can/vxcan.c | 4 ++++
> include/linux/can/skb.h | 4 ++++
> include/linux/skbuff.h | 3 +++
> net/can/Kconfig | 1 +
> net/can/af_can.c | 5 +++++
> net/can/raw.c | 10 ++++++++--
> net/core/skbuff.c | 7 +++++++
> 7 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/can/vxcan.c b/drivers/net/can/vxcan.c
> index 577a80300514..93701a698008 100644
> --- a/drivers/net/can/vxcan.c
> +++ b/drivers/net/can/vxcan.c
> @@ -39,6 +39,7 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *oskb, struct net_device *dev)
> struct net_device *peer;
> struct canfd_frame *cfd = (struct canfd_frame *)oskb->data;
> struct net_device_stats *peerstats, *srcstats = &dev->stats;
> + struct can_skb_ext *can_ext;
> struct sk_buff *skb;
> u8 len;
>
> @@ -66,6 +67,9 @@ static netdev_tx_t vxcan_xmit(struct sk_buff *oskb, struct net_device *dev)
> skb->pkt_type = PACKET_BROADCAST;
> skb->dev = peer;
> skb->ip_summed = CHECKSUM_UNNECESSARY;
> + can_ext = skb_ext_add(skb, SKB_EXT_CAN);
> + if (can_ext)
> + can_ext->local_origin = false;
>
> len = cfd->can_id & CAN_RTR_FLAG ? 0 : cfd->len;
> if (netif_rx(skb) == NET_RX_SUCCESS) {
> diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
> index fdb22b00674a..401b08890d74 100644
> --- a/include/linux/can/skb.h
> +++ b/include/linux/can/skb.h
> @@ -55,6 +55,10 @@ struct can_skb_priv {
> struct can_frame cf[];
> };
>
> +struct can_skb_ext {
> + bool local_origin;
> +};
> +
> static inline struct can_skb_priv *can_skb_prv(struct sk_buff *skb)
> {
> return (struct can_skb_priv *)(skb->head);
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 3270cb72e4d8..d39e70e5f7f2 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4563,6 +4563,9 @@ enum skb_ext_id {
> #endif
> #if IS_ENABLED(CONFIG_MCTP_FLOWS)
> SKB_EXT_MCTP,
> +#endif
> +#if IS_ENABLED(CONFIG_CAN)
> + SKB_EXT_CAN,
> #endif
> SKB_EXT_NUM, /* must be last */
> };
> diff --git a/net/can/Kconfig b/net/can/Kconfig
> index a9ac5ffab286..eb826e3771fe 100644
> --- a/net/can/Kconfig
> +++ b/net/can/Kconfig
> @@ -5,6 +5,7 @@
>
> menuconfig CAN
> tristate "CAN bus subsystem support"
> + select SKB_EXTENSIONS
> help
> Controller Area Network (CAN) is a slow (up to 1Mbit/s) serial
> communications protocol. Development of the CAN bus started in
> diff --git a/net/can/af_can.c b/net/can/af_can.c
> index 1fb49d51b25d..329c540d3ddf 100644
> --- a/net/can/af_can.c
> +++ b/net/can/af_can.c
> @@ -201,6 +201,7 @@ int can_send(struct sk_buff *skb, int loop)
> struct sk_buff *newskb = NULL;
> struct canfd_frame *cfd = (struct canfd_frame *)skb->data;
> struct can_pkg_stats *pkg_stats = dev_net(skb->dev)->can.pkg_stats;
> + struct can_skb_ext *can_ext;
> int err = -EINVAL;
>
> if (skb->len == CAN_MTU) {
> @@ -240,6 +241,10 @@ int can_send(struct sk_buff *skb, int loop)
> skb_reset_network_header(skb);
> skb_reset_transport_header(skb);
>
> + can_ext = skb_ext_add(skb, SKB_EXT_CAN);
> + if (can_ext)
> + can_ext->local_origin = true;
> +
> if (loop) {
> /* local loopback of sent CAN frames */
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index b7dbb57557f3..cba18cdf017f 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -121,6 +121,7 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
> {
> struct sock *sk = (struct sock *)data;
> struct raw_sock *ro = raw_sk(sk);
> + struct can_skb_ext *can_ext;
> struct sockaddr_can *addr;
> struct sk_buff *skb;
> unsigned int *pflags;
> @@ -173,8 +174,13 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
> /* add CAN specific message flags for raw_recvmsg() */
> pflags = raw_flags(skb);
> *pflags = 0;
> - if (oskb->sk)
> - *pflags |= MSG_DONTROUTE;
> +
> + can_ext = skb_ext_find(oskb, SKB_EXT_CAN);
> + if (can_ext) {
> + if (can_ext->local_origin)
> + *pflags |= MSG_DONTROUTE;
> + }
> +
> if (oskb->sk == sk)
> *pflags |= MSG_CONFIRM;
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 475183f37891..5a5409ccb767 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -61,6 +61,7 @@
> #include <linux/if_vlan.h>
> #include <linux/mpls.h>
> #include <linux/kcov.h>
> +#include <linux/can/skb.h>
>
> #include <net/protocol.h>
> #include <net/dst.h>
> @@ -4338,6 +4339,9 @@ static const u8 skb_ext_type_len[] = {
> #if IS_ENABLED(CONFIG_MCTP_FLOWS)
> [SKB_EXT_MCTP] = SKB_EXT_CHUNKSIZEOF(struct mctp_flow),
> #endif
> +#if IS_ENABLED(CONFIG_CAN)
> + [SKB_EXT_CAN] = SKB_EXT_CHUNKSIZEOF(struct can_skb_ext),
> +#endif
> };
>
> static __always_inline unsigned int skb_ext_total_length(void)
> @@ -4357,6 +4361,9 @@ static __always_inline unsigned int skb_ext_total_length(void)
> #endif
> #if IS_ENABLED(CONFIG_MCTP_FLOWS)
> skb_ext_type_len[SKB_EXT_MCTP] +
> +#endif
> +#if IS_ENABLED(CONFIG_CAN)
> + skb_ext_type_len[SKB_EXT_CAN] +
> #endif
> 0;
> }
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