can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer
This patch adds the function can_skb_get_frame_len() which returns the length of a CAN frame on the data link layer, including Start-of-frame, Identifier, various other bits, the actual data, the CRC, the End-of-frame, the Inter frame spacing. Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com> Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com> Co-developed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr> Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de> Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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@ -38,3 +38,53 @@ u8 can_fd_len2dlc(u8 len)
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return len2dlc[len];
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}
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EXPORT_SYMBOL_GPL(can_fd_len2dlc);
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/**
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* can_skb_get_frame_len() - Calculate the CAN Frame length in bytes
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* of a given skb.
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* @skb: socket buffer of a CAN message.
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*
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* Do a rough calculation: bit stuffing is ignored and length in bits
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* is rounded up to a length in bytes.
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*
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* Rationale: this function is to be used for the BQL functions
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* (netdev_sent_queue() and netdev_completed_queue()) which expect a
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* value in bytes. Just using skb->len is insufficient because it will
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* return the constant value of CAN(FD)_MTU. Doing the bit stuffing
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* calculation would be too expensive in term of computing resources
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* for no noticeable gain.
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*
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* Remarks: The payload of CAN FD frames with BRS flag are sent at a
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* different bitrate. Currently, the can-utils canbusload tool does
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* not support CAN-FD yet and so we could not run any benchmark to
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* measure the impact. There might be possible improvement here.
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*
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* Return: length in bytes.
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*/
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unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
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{
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const struct canfd_frame *cf = (const struct canfd_frame *)skb->data;
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u8 len;
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if (can_is_canfd_skb(skb))
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len = canfd_sanitize_len(cf->len);
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else if (cf->can_id & CAN_RTR_FLAG)
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len = 0;
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else
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len = cf->len;
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if (can_is_canfd_skb(skb)) {
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if (cf->can_id & CAN_EFF_FLAG)
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len += CANFD_FRAME_OVERHEAD_EFF;
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else
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len += CANFD_FRAME_OVERHEAD_SFF;
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} else {
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if (cf->can_id & CAN_EFF_FLAG)
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len += CAN_FRAME_OVERHEAD_EFF;
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else
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len += CAN_FRAME_OVERHEAD_SFF;
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}
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return len;
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}
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EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
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@ -1,10 +1,127 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
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* Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
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*/
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#ifndef _CAN_LENGTH_H
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#define _CAN_LENGTH_H
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/*
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* Size of a Classical CAN Standard Frame
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*
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* Name of Field Bits
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* ---------------------------------------------------------
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* Start-of-frame 1
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* Identifier 11
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* Remote transmission request (RTR) 1
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* Identifier extension bit (IDE) 1
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* Reserved bit (r0) 1
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* Data length code (DLC) 4
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* Data field 0...64
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* CRC 15
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* CRC delimiter 1
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* ACK slot 1
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* ACK delimiter 1
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* End-of-frame (EOF) 7
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* Inter frame spacing 3
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*
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* rounded up and ignoring bitstuffing
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*/
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#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
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/*
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* Size of a Classical CAN Extended Frame
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*
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* Name of Field Bits
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* ---------------------------------------------------------
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* Start-of-frame 1
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* Identifier A 11
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* Substitute remote request (SRR) 1
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* Identifier extension bit (IDE) 1
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* Identifier B 18
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* Remote transmission request (RTR) 1
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* Reserved bits (r1, r0) 2
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* Data length code (DLC) 4
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* Data field 0...64
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* CRC 15
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* CRC delimiter 1
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* ACK slot 1
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* ACK delimiter 1
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* End-of-frame (EOF) 7
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* Inter frame spacing 3
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*
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* rounded up and ignoring bitstuffing
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*/
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#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
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/*
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* Size of a CAN-FD Standard Frame
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*
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* Name of Field Bits
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* ---------------------------------------------------------
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* Start-of-frame 1
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* Identifier 11
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* Reserved bit (r1) 1
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* Identifier extension bit (IDE) 1
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* Flexible data rate format (FDF) 1
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* Reserved bit (r0) 1
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* Bit Rate Switch (BRS) 1
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* Error Status Indicator (ESI) 1
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* Data length code (DLC) 4
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* Data field 0...512
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* Stuff Bit Count (SBC) 0...16: 4 20...64:5
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* CRC 0...16: 17 20...64:21
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* CRC delimiter (CD) 1
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* ACK slot (AS) 1
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* ACK delimiter (AD) 1
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* End-of-frame (EOF) 7
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* Inter frame spacing 3
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*
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* assuming CRC21, rounded up and ignoring bitstuffing
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*/
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#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
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/*
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* Size of a CAN-FD Extended Frame
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*
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* Name of Field Bits
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* ---------------------------------------------------------
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* Start-of-frame 1
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* Identifier A 11
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* Substitute remote request (SRR) 1
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* Identifier extension bit (IDE) 1
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* Identifier B 18
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* Reserved bit (r1) 1
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* Flexible data rate format (FDF) 1
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* Reserved bit (r0) 1
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* Bit Rate Switch (BRS) 1
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* Error Status Indicator (ESI) 1
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* Data length code (DLC) 4
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* Data field 0...512
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* Stuff Bit Count (SBC) 0...16: 4 20...64:5
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* CRC 0...16: 17 20...64:21
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* CRC delimiter (CD) 1
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* ACK slot (AS) 1
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* ACK delimiter (AD) 1
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* End-of-frame (EOF) 7
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* Inter frame spacing 3
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*
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* assuming CRC21, rounded up and ignoring bitstuffing
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*/
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#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
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/*
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* Maximum size of a Classical CAN frame
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* (rounded up and ignoring bitstuffing)
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*/
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#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
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/*
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* Maximum size of a CAN-FD frame
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* (rounded up and ignoring bitstuffing)
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*/
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#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
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/*
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* can_cc_dlc2len(value) - convert a given data length code (dlc) of a
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* Classical CAN frame into a valid data length of max. 8 bytes.
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@ -45,6 +162,9 @@ u8 can_fd_dlc2len(u8 dlc);
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/* map the sanitized data length to an appropriate data length code */
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u8 can_fd_len2dlc(u8 len);
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/* calculate the CAN Frame length in bytes of a given skb */
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unsigned int can_skb_get_frame_len(const struct sk_buff *skb);
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/* map the data length to an appropriate data link layer length */
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static inline u8 canfd_sanitize_len(u8 len)
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{
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