Commit b5af9bdb authored by Alexander Aring's avatar Alexander Aring Committed by Marcel Holtmann
Browse files

6lowpan: rework tc and flow label handling 



This patch reworks the handling of compression/decompression of traffic
class and flow label handling. The current method is hard to understand,
also doesn't checks if we can read the buffer from skb length.

I tried to put the shifting operations into static inline functions and
comment each steps which I did there to make it hopefully somewhat more
readable. The big mess to deal with that is the that the ipv6 header
bring the order "DSCP + ECN" but iphc uses "ECN + DSCP". Additional the
DCSP + ECN bits are splitted in ipv6_hdr inside the priority and
flow_lbl[0] fields.

I tested these compressions by using fakelb 802.15.4 driver and
manipulate the tc and flow label fields manually in function
"__ip6_local_out" before the skb will be send to lower layers. Then I
looked up the tc and flow label fields in wireshark on a wpan and lowpan
interface.

Signed-off-by: default avatarAlexander Aring <alex.aring@gmail.com>
Signed-off-by: default avatarMarcel Holtmann <marcel@holtmann.org>
parent c8a3e7eb

net/6lowpan/iphc.c

+205 −85
Original line number Diff line number Diff line
@@ -346,6 +346,108 @@ static int lowpan_uncompress_multicast_daddr(struct sk_buff *skb, 
	return 0;

}



/* get the ecn values from iphc tf format and set it to ipv6hdr */

static inline void lowpan_iphc_tf_set_ecn(struct ipv6hdr *hdr, const u8 *tf)

{

	/* get the two higher bits which is ecn */

	u8 ecn = tf[0] & 0xc0;



	/* ECN takes 0x30 in hdr->flow_lbl[0] */

	hdr->flow_lbl[0] |= (ecn >> 2);

}



/* get the dscp values from iphc tf format and set it to ipv6hdr */

static inline void lowpan_iphc_tf_set_dscp(struct ipv6hdr *hdr, const u8 *tf)

{

	/* DSCP is at place after ECN */

	u8 dscp = tf[0] & 0x3f;



	/* The four highest bits need to be set at hdr->priority */

	hdr->priority |= ((dscp & 0x3c) >> 2);

	/* The two lower bits is part of hdr->flow_lbl[0] */

	hdr->flow_lbl[0] |= ((dscp & 0x03) << 6);

}



/* get the flow label values from iphc tf format and set it to ipv6hdr */

static inline void lowpan_iphc_tf_set_lbl(struct ipv6hdr *hdr, const u8 *lbl)

{

	/* flow label is always some array started with lower nibble of

	 * flow_lbl[0] and followed with two bytes afterwards. Inside inline

	 * data the flow_lbl position can be different, which will be handled

	 * by lbl pointer. E.g. case "01" vs "00" the traffic class is 8 bit

	 * shifted, the different lbl pointer will handle that.

	 *

	 * The flow label will started at lower nibble of flow_lbl[0], the

	 * higher nibbles are part of DSCP + ECN.

	 */

	hdr->flow_lbl[0] |= lbl[0] & 0x0f;

	memcpy(&hdr->flow_lbl[1], &lbl[1], 2);

}



/* lowpan_iphc_tf_decompress - decompress the traffic class.

 *	This function will return zero on success, a value lower than zero if

 *	failed.

 */

static int lowpan_iphc_tf_decompress(struct sk_buff *skb, struct ipv6hdr *hdr,

				     u8 val)

{

	u8 tf[4];



	/* Traffic Class and Flow Label */

	switch (val) {

	case LOWPAN_IPHC_TF_00:

		/* ECN + DSCP + 4-bit Pad + Flow Label (4 bytes) */

		if (lowpan_fetch_skb(skb, tf, 4))

			return -EINVAL;



		/*                      1                   2                   3

		 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

		 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

		 * |ECN|   DSCP    |  rsv  |             Flow Label                |

		 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

		 */

		lowpan_iphc_tf_set_ecn(hdr, tf);

		lowpan_iphc_tf_set_dscp(hdr, tf);

		lowpan_iphc_tf_set_lbl(hdr, &tf[1]);

		break;

	case LOWPAN_IPHC_TF_01:

		/* ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided. */

		if (lowpan_fetch_skb(skb, tf, 3))

			return -EINVAL;



		/*                     1                   2

		 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3

		 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

		 * |ECN|rsv|             Flow Label                |

		 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

		 */

		lowpan_iphc_tf_set_ecn(hdr, tf);

		lowpan_iphc_tf_set_lbl(hdr, &tf[0]);

		break;

	case LOWPAN_IPHC_TF_10:

		/* ECN + DSCP (1 byte), Flow Label is elided. */

		if (lowpan_fetch_skb(skb, tf, 1))

			return -EINVAL;



		/*  0 1 2 3 4 5 6 7

		 * +-+-+-+-+-+-+-+-+

		 * |ECN|   DSCP    |

		 * +-+-+-+-+-+-+-+-+

		 */

		lowpan_iphc_tf_set_ecn(hdr, tf);

		lowpan_iphc_tf_set_dscp(hdr, tf);

		break;

	case LOWPAN_IPHC_TF_11:

		/* Traffic Class and Flow Label are elided */

		break;

	default:

		WARN_ON_ONCE(1);

		return -EINVAL;

	}



	return 0;

}



/* TTL uncompression values */

static const u8 lowpan_ttl_values[] = {

	[LOWPAN_IPHC_HLIM_01] = 1,
@@ -357,7 +459,7 @@ int lowpan_header_decompress(struct sk_buff *skb, const struct net_device *dev, 
			     const void *daddr, const void *saddr)

{

	struct ipv6hdr hdr = {};

	u8 iphc0, iphc1, tmp = 0;

	u8 iphc0, iphc1;

	int err;



	raw_dump_table(__func__, "raw skb data dump uncompressed",
@@ -373,49 +475,10 @@ int lowpan_header_decompress(struct sk_buff *skb, const struct net_device *dev, 


	hdr.version = 6;



	/* Traffic Class and Flow Label */

	switch (iphc0 & LOWPAN_IPHC_TF_MASK) {

	/* Traffic Class and FLow Label carried in-line

	 * ECN + DSCP + 4-bit Pad + Flow Label (4 bytes)

	 */

	case LOWPAN_IPHC_TF_00:

		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))

			return -EINVAL;



		memcpy(&hdr.flow_lbl, &skb->data[0], 3);

		skb_pull(skb, 3);

		hdr.priority = ((tmp >> 2) & 0x0f);

		hdr.flow_lbl[0] = ((tmp >> 2) & 0x30) | (tmp << 6) |

					(hdr.flow_lbl[0] & 0x0f);

		break;

	/* Flow Label carried in-line

	 * ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided

	 */

	case LOWPAN_IPHC_TF_01:

		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))

			return -EINVAL;



		hdr.flow_lbl[0] = (tmp & 0x0F) | ((tmp >> 2) & 0x30);

		memcpy(&hdr.flow_lbl[1], &skb->data[0], 2);

		skb_pull(skb, 2);

		break;

	/* Traffic class carried in-line

	 * ECN + DSCP (1 byte), Flow Label is elided

	 */

	case LOWPAN_IPHC_TF_10:

		if (lowpan_fetch_skb(skb, &tmp, sizeof(tmp)))

			return -EINVAL;



		hdr.priority = ((tmp >> 2) & 0x0f);

		hdr.flow_lbl[0] = ((tmp << 6) & 0xC0) | ((tmp >> 2) & 0x30);

		break;

	/* Traffic Class and Flow Label are elided */

	case LOWPAN_IPHC_TF_11:

		break;

	default:

		WARN_ON_ONCE(1);

		break;

	}

	err = lowpan_iphc_tf_decompress(skb, &hdr,

					iphc0 & LOWPAN_IPHC_TF_MASK);

	if (err < 0)

		return err;



	/* Next Header */

	if (!(iphc0 & LOWPAN_IPHC_NH)) {
@@ -550,10 +613,105 @@ static u8 lowpan_compress_addr_64(u8 **hc_ptr, const struct in6_addr *ipaddr, 
		return dam;

}



/* lowpan_iphc_get_tc - get the ECN + DCSP fields in hc format */

static inline u8 lowpan_iphc_get_tc(const struct ipv6hdr *hdr)

{

	u8 dscp, ecn;



	/* hdr->priority contains the higher bits of dscp, lower are part of

	 * flow_lbl[0]. Note ECN, DCSP is swapped in ipv6 hdr.

	 */

	dscp = (hdr->priority << 2) | ((hdr->flow_lbl[0] & 0xc0) >> 6);

	/* ECN is at the two lower bits from first nibble of flow_lbl[0] */

	ecn = (hdr->flow_lbl[0] & 0x30);

	/* for pretty debug output, also shift ecn to get the ecn value */

	pr_debug("ecn 0x%02x dscp 0x%02x\n", ecn >> 4, dscp);

	/* ECN is at 0x30 now, shift it to have ECN + DCSP */

	return (ecn << 2) | dscp;

}



/* lowpan_iphc_is_flow_lbl_zero - check if flow label is zero */

static inline bool lowpan_iphc_is_flow_lbl_zero(const struct ipv6hdr *hdr)

{

	return ((!(hdr->flow_lbl[0] & 0x0f)) &&

		!hdr->flow_lbl[1] && !hdr->flow_lbl[2]);

}



/* lowpan_iphc_tf_compress - compress the traffic class which is set by

 *	ipv6hdr. Return the corresponding format identifier which is used.

 */

static u8 lowpan_iphc_tf_compress(u8 **hc_ptr, const struct ipv6hdr *hdr)

{

	/* get ecn dscp data in a byteformat as: ECN(hi) + DSCP(lo) */

	u8 tc = lowpan_iphc_get_tc(hdr), tf[4], val;



	/* printout the traffic class in hc format */

	pr_debug("tc 0x%02x\n", tc);



	if (lowpan_iphc_is_flow_lbl_zero(hdr)) {

		if (!tc) {

			/* 11:  Traffic Class and Flow Label are elided. */

			val = LOWPAN_IPHC_TF_11;

		} else {

			/* 10:  ECN + DSCP (1 byte), Flow Label is elided.

			 *

			 *  0 1 2 3 4 5 6 7

			 * +-+-+-+-+-+-+-+-+

			 * |ECN|   DSCP    |

			 * +-+-+-+-+-+-+-+-+

			 */

			lowpan_push_hc_data(hc_ptr, &tc, sizeof(tc));

			val = LOWPAN_IPHC_TF_10;

		}

	} else {

		/* check if dscp is zero, it's after the first two bit */

		if (!(tc & 0x3f)) {

			/* 01:  ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided

			 *

			 *                     1                   2

			 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3

			 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

			 * |ECN|rsv|             Flow Label                |

			 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

			 */

			memcpy(&tf[0], &hdr->flow_lbl[0], 3);

			/* zero the highest 4-bits, contains DCSP + ECN */

			tf[0] &= ~0xf0;

			/* set ECN */

			tf[0] |= (tc & 0xc0);



			lowpan_push_hc_data(hc_ptr, tf, 3);

			val = LOWPAN_IPHC_TF_01;

		} else {

			/* 00:  ECN + DSCP + 4-bit Pad + Flow Label (4 bytes)

			 *

			 *                      1                   2                   3

			 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

			 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

			 * |ECN|   DSCP    |  rsv  |             Flow Label                |

			 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

			 */

			memcpy(&tf[0], &tc, sizeof(tc));

			/* highest nibble of flow_lbl[0] is part of DSCP + ECN

			 * which will be the 4-bit pad and will be filled with

			 * zeros afterwards.

			 */

			memcpy(&tf[1], &hdr->flow_lbl[0], 3);

			/* zero the 4-bit pad, which is reserved */

			tf[1] &= ~0xf0;



			lowpan_push_hc_data(hc_ptr, tf, 4);

			val = LOWPAN_IPHC_TF_00;

		}

	}



	return val;

}



int lowpan_header_compress(struct sk_buff *skb, const struct net_device *dev,

			   const void *daddr, const void *saddr)

{

	u8 tmp, iphc0, iphc1, *hc_ptr;

	u8 iphc0, iphc1, *hc_ptr;

	struct ipv6hdr *hdr;

	u8 head[LOWPAN_IPHC_MAX_HC_BUF_LEN] = {};

	int ret, addr_type;
@@ -588,46 +746,8 @@ int lowpan_header_compress(struct sk_buff *skb, const struct net_device *dev, 
	raw_dump_table(__func__, "sending raw skb network uncompressed packet",

		       skb->data, skb->len);



	/* Traffic class, flow label

	 * If flow label is 0, compress it. If traffic class is 0, compress it

	 * We have to process both in the same time as the offset of traffic

	 * class depends on the presence of version and flow label

	 */



	/* hc format of TC is ECN | DSCP , original one is DSCP | ECN */

	tmp = (hdr->priority << 4) | (hdr->flow_lbl[0] >> 4);

	tmp = ((tmp & 0x03) << 6) | (tmp >> 2);



	if (((hdr->flow_lbl[0] & 0x0F) == 0) &&

	    (hdr->flow_lbl[1] == 0) && (hdr->flow_lbl[2] == 0)) {

		/* flow label can be compressed */

		iphc0 |= LOWPAN_IPHC_TF_10;

		if ((hdr->priority == 0) &&

		    ((hdr->flow_lbl[0] & 0xF0) == 0)) {

			/* compress (elide) all */

			iphc0 |= LOWPAN_IPHC_TF_11;

		} else {

			/* compress only the flow label */

			*hc_ptr = tmp;

			hc_ptr += 1;

		}

	} else {

		/* Flow label cannot be compressed */

		if ((hdr->priority == 0) &&

		    ((hdr->flow_lbl[0] & 0xF0) == 0)) {

			/* compress only traffic class */

			iphc0 |= LOWPAN_IPHC_TF_01;

			*hc_ptr = (tmp & 0xc0) | (hdr->flow_lbl[0] & 0x0F);

			memcpy(hc_ptr + 1, &hdr->flow_lbl[1], 2);

			hc_ptr += 3;

		} else {

			/* compress nothing */

			memcpy(hc_ptr, hdr, 4);

			/* replace the top byte with new ECN | DSCP format */

			*hc_ptr = tmp;

			hc_ptr += 4;

		}

	}

	/* Traffic Class, Flow Label compression */

	iphc0 |= lowpan_iphc_tf_compress(&hc_ptr, hdr);



	/* NOTE: payload length is always compressed */

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