From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-can@vger.kernel.org,
Wolfgang Grandegger <wg@grandegger.com>,
"David S . Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>,
Oliver Neukum <oneukum@suse.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>,
"open list:USB ACM DRIVER" <linux-usb@vger.kernel.org>
Subject: Re: [PATCH v2 2/6] can: dev: add a helper function to get the correct length of Classical frames
Date: Wed, 30 Sep 2020 17:21:20 +0200 [thread overview]
Message-ID: <1798400d-abc1-e6dd-2d19-41e82ca6e43e@pengutronix.de> (raw)
In-Reply-To: <20200930144602.10290-3-mailhol.vincent@wanadoo.fr>
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On 9/30/20 4:45 PM, Vincent Mailhol wrote:
> In classical CAN, the length of the data (i.e. CAN payload) is not
> always equal to the DLC! If the frame is a Remote Transmission Request
> (RTR), data length is always zero regardless of DLC value and else, if
> the DLC is greater than 8, the length is 8. Contrary to common belief,
> ISO 11898-1 Chapter 8.4.2.3 (DLC field) do allow DLCs greater than 8
> for Classical Frames and specifies that those DLCs shall indicate that
> the data field is 8 bytes long.
>
> Above facts are widely unknown and so many developpers uses the "len"
> field of "struct canfd_frame" to get the length of classical CAN
> frames: this is incorrect!
>
> This patch introduces function get_can_len() which can be used in
> remediation. The function takes the SKB as an input in order to be
> able to determine if the frame is classical or FD.
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> ---
> include/linux/can/dev.h | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
> index 5e3d45525bd3..72a8a60c0094 100644
> --- a/include/linux/can/dev.h
> +++ b/include/linux/can/dev.h
> @@ -177,6 +177,29 @@ u8 can_dlc2len(u8 can_dlc);
> /* map the sanitized data length to an appropriate data length code */
> u8 can_len2dlc(u8 len);
>
> +/*
> + * get_can_len(skb) - get the length of the CAN payload.
> + *
> + * In classical CAN, the length of the data (i.e. CAN payload) is not
> + * always equal to the DLC! If the frame is a Remote Transmission
> + * Request (RTR), data length is always zero regardless of DLC value
> + * and else, if the DLC is greater than 8, the length is 8. Contrary
> + * to common belief, ISO 11898-1 Chapter 8.4.2.3 (DLC field) do allow
> + * DLCs greater than 8 for Classical Frames and specifies that those
> + * DLCs shall indicate that the data field is 8 bytes long.
> + */
> +static inline int get_can_len(struct sk_buff *skb)
make this return an u8
make the skb const
> +{
> + struct canfd_frame *cf = (struct canfd_frame *)skb->data;
const
> +
> + if (can_is_canfd_skb(skb))
> + return min_t(__u8, cf->len, CANFD_MAX_DLEN);
u8
> + else if (cf->can_id & CAN_RTR_FLAG)
> + return 0;
> + else
> + return min_t(__u8, cf->len, CAN_MAX_DLEN);
u8
> +}
> +
> struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max,
> unsigned int txqs, unsigned int rxqs);
> #define alloc_candev(sizeof_priv, echo_skb_max) \
>
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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next prev parent reply other threads:[~2020-09-30 15:22 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-26 17:57 [PATCH 0/6] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-09-26 17:57 ` [PATCH 1/6] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-09-26 17:57 ` [PATCH 2/6] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-09-26 17:57 ` [PATCH 3/6] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-09-26 17:57 ` [PATCH 4/6] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-09-26 17:57 ` [PATCH 6/6] USB: cdc-acm: blacklist ETAS ES58X device Vincent Mailhol
2020-09-27 5:45 ` Greg Kroah-Hartman
2020-09-27 5:52 ` Greg Kroah-Hartman
2020-09-29 2:15 ` Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 0/6] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 1/6] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 2/6] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-09-30 15:21 ` Marc Kleine-Budde [this message]
2020-10-01 15:45 ` [PATCH v2 2/6] can: dev: add a helper function Vincent Mailhol
2020-10-01 15:51 ` Marc Kleine-Budde
2020-09-30 14:45 ` [PATCH v2 3/6] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 4/6] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-09-30 14:45 ` [PATCH v2 6/6] usb: cdc-acm: add quirk to blacklist ETAS ES58X devices Vincent Mailhol
[not found] ` <20200930144602.10290-6-mailhol.vincent@wanadoo.fr>
2020-09-30 16:18 ` [PATCH v2 5/6] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces Greg Kroah-Hartman
2020-10-01 15:56 ` Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 0/7] can: add support for ETAS ES58X CAN USB Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 1/7] can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 2/7] can: dev: fix type of get_can_dlc() and get_canfd_dlc() macros Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 3/7] can: dev: add a helper function to get the correct length of Classical frames Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 4/7] can: dev: __can_get_echo_skb(): fix the return length Vincent Mailhol
2020-10-02 15:41 ` [PATCH v3 5/7] can: dev: add a helper function to calculate the duration of one bit Vincent Mailhol
2020-10-04 11:06 ` Marc Kleine-Budde
2020-10-04 11:10 ` Marc Kleine-Budde
2020-10-02 15:41 ` [PATCH v3 7/7] usb: cdc-acm: add quirk to blacklist ETAS ES58X devices Vincent Mailhol
2020-10-05 11:14 ` Greg Kroah-Hartman
[not found] ` <20201002154219.4887-7-mailhol.vincent@wanadoo.fr>
2020-10-04 12:06 ` [PATCH v3 6/7] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces Marc Kleine-Budde
2020-10-10 8:12 ` Vincent Mailhol
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