Re: [RFC PATCH v5 3/5] can: dev: add CAN XL support

Oliver Hartkopp <socketcan@xxxxxxxxxxxx> · Tue, 19 Jul 2022 16:38:06 +0200

On 19.07.22 16:11, Vincent Mailhol wrote:
On Tue. 19 Jul. 2022, 20:44, Oliver Hartkopp <socketcan@xxxxxxxxxxxx> wrote:
Extend the CAN device driver infrastructure to handle CAN XL frames.
This especially addresses the increased data length which is extended
to uint16 for CAN XL.

Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
---
  drivers/net/can/dev/rx-offload.c |  2 +-
  drivers/net/can/dev/skb.c        | 49 ++++++++++++++++++++++++++------
  include/linux/can/skb.h          |  5 +++-
  3 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/drivers/net/can/dev/rx-offload.c b/drivers/net/can/dev/rx-offload.c
index a32a01c172d4..8505e547e922 100644
--- a/drivers/net/can/dev/rx-offload.c
+++ b/drivers/net/can/dev/rx-offload.c
@@ -245,11 +245,11 @@ unsigned int can_rx_offload_get_echo_skb(struct can_rx_offload *offload,
                                          unsigned int *frame_len_ptr)
  {
         struct net_device *dev = offload->dev;
         struct net_device_stats *stats = &dev->stats;
         struct sk_buff *skb;
-       u8 len;
+       unsigned int len;
         int err;

         skb = __can_get_echo_skb(dev, idx, &len, frame_len_ptr);
         if (!skb)
                 return 0;
diff --git a/drivers/net/can/dev/skb.c b/drivers/net/can/dev/skb.c
index 8bb62dd864c8..8531e0c39d1c 100644
--- a/drivers/net/can/dev/skb.c
+++ b/drivers/net/can/dev/skb.c
@@ -53,11 +53,12 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
         BUG_ON(idx >= priv->echo_skb_max);

         /* check flag whether this packet has to be looped back */
         if (!(dev->flags & IFF_ECHO) ||
             (skb->protocol != htons(ETH_P_CAN) &&
-            skb->protocol != htons(ETH_P_CANFD))) {
+            skb->protocol != htons(ETH_P_CANFD) &&
+            skb->protocol != htons(ETH_P_CANXL))) {
                 kfree_skb(skb);
                 return 0;
         }

         if (!priv->echo_skb[idx]) {
@@ -86,12 +87,12 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
         return 0;
  }
  EXPORT_SYMBOL_GPL(can_put_echo_skb);

  struct sk_buff *
-__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr,
-                  unsigned int *frame_len_ptr)
+__can_get_echo_skb(struct net_device *dev, unsigned int idx,
+                  unsigned int *len_ptr, unsigned int *frame_len_ptr)
  {
         struct can_priv *priv = netdev_priv(dev);

         if (idx >= priv->echo_skb_max) {
                 netdev_err(dev, "%s: BUG! Trying to access can_priv::echo_skb out of bounds (%u/max %u)\n",
@@ -103,17 +104,13 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr,
                 /* Using "struct canfd_frame::len" for the frame
                  * length is supported on both CAN and CANFD frames.
                  */
                 struct sk_buff *skb = priv->echo_skb[idx];
                 struct can_skb_priv *can_skb_priv = can_skb_prv(skb);
-               struct canfd_frame *cf = (struct canfd_frame *)skb->data;

                 /* get the real payload length for netdev statistics */
-               if (cf->can_id & CAN_RTR_FLAG)
-                       *len_ptr = 0;
-               else
-                       *len_ptr = cf->len;
+               *len_ptr = can_skb_get_data_len(skb);

                 if (frame_len_ptr)
                         *frame_len_ptr = can_skb_priv->frame_len;

                 priv->echo_skb[idx] = NULL;
@@ -139,11 +136,11 @@ __can_get_echo_skb(struct net_device *dev, unsigned int idx, u8 *len_ptr,
   */
  unsigned int can_get_echo_skb(struct net_device *dev, unsigned int idx,
                               unsigned int *frame_len_ptr)
  {
         struct sk_buff *skb;
-       u8 len;
+       unsigned int len;

         skb = __can_get_echo_skb(dev, idx, &len, frame_len_ptr);
         if (!skb)
                 return 0;

@@ -244,10 +241,41 @@ struct sk_buff *alloc_canfd_skb(struct net_device *dev,

         return skb;
  }
  EXPORT_SYMBOL_GPL(alloc_canfd_skb);

+struct sk_buff *alloc_canxl_skb(struct net_device *dev,
+                               struct canxl_frame **cfx)
+{
+       struct sk_buff *skb;
+
+       skb = netdev_alloc_skb(dev, sizeof(struct can_skb_priv) +
+                              sizeof(struct canxl_frame));

I am confused. In this message:
https://lore.kernel.org/linux-can/3dcc85f8-2c02-dfe5-de23-d022f3fc56be@xxxxxxxxxxxx/
you said that you "vote for selecting the 'truncated' option only"
(which is OK with me). But here, you are allocating the full size. If
we always want truncated frames, shouldn't we allocate the exact size
frame length here?

No confusion.

The API to the user space is 'truncated' option only.

The data structure inside the kernel sizeof(struct can[|fd|xl]_frame).

See:
https://lore.kernel.org/linux-can/4c79233f-1301-d5c7-7698-38d39d8702aa@xxxxxxxxxxxx/

---8<---

As the sk_buffs are only allocated once and are not copied inside the
kernel there should be no remarkable drawbacks whether we allocate
CAN_MTU skbs or CANXL_MTU skbs.

AFAICS both skbs will fit into a single page.

---8<---

It is just easier and safe.

(..)

@@ -302,10 +330,13 @@ bool can_dropped_invalid_skb(struct net_device *dev, struct sk_buff *skb)
                         goto inval_skb;
         } else if (skb->protocol == htons(ETH_P_CANFD)) {
                 if (unlikely(skb->len != CANFD_MTU ||
                              cfd->len > CANFD_MAX_DLEN))
                         goto inval_skb;
+       } else if (skb->protocol == htons(ETH_P_CANXL)) {

Nitpick but with the growing list, I would see a switch
(skb->protocol) rather than the cascade of if.

+               if (unlikely(!can_is_canxl_skb(skb)))
+                       goto inval_skb;
         } else {

default:

                 goto inval_skb;
         }

Yes. Good idea!

Will change that.


Best regards,
Oliver






