From 77cffe23c1f88835f6bd7b47bfa0c060c2969828 Mon Sep 17 00:00:00 2001 From: Tom Herbert Date: Wed, 27 Aug 2014 21:26:46 -0700 Subject: net: Clarification of CHECKSUM_UNNECESSARY This patch: - Clarifies the specific requirements of devices returning CHECKSUM_UNNECESSARY (comments in skbuff.h). - Adds csum_level field to skbuff. This is used to express how many checksums are covered by CHECKSUM_UNNECESSARY (stores n - 1). This replaces the overloading of skb->encapsulation, that field is is now only used to indicate inner headers are valid. - Change __skb_checksum_validate_needed to "consume" each checksum as indicated by csum_level as layers of the the packet are parsed. - Remove skb_pop_rcv_encapsulation, no longer needed in the new csum_level model. Signed-off-by: Tom Herbert Signed-off-by: David S. Miller --- include/linux/skbuff.h | 74 ++++++++++++++++++++++++++++++++++---------------- 1 file changed, 51 insertions(+), 23 deletions(-) (limited to 'include') diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 3c9574c80933..c93b5859a772 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -47,11 +47,29 @@ * * The hardware you're dealing with doesn't calculate the full checksum * (as in CHECKSUM_COMPLETE), but it does parse headers and verify checksums - * for specific protocols e.g. TCP/UDP/SCTP, then, for such packets it will - * set CHECKSUM_UNNECESSARY if their checksums are okay. skb->csum is still - * undefined in this case though. It is a bad option, but, unfortunately, - * nowadays most vendors do this. Apparently with the secret goal to sell - * you new devices, when you will add new protocol to your host, f.e. IPv6 8) + * for specific protocols. For such packets it will set CHECKSUM_UNNECESSARY + * if their checksums are okay. skb->csum is still undefined in this case + * though. It is a bad option, but, unfortunately, nowadays most vendors do + * this. Apparently with the secret goal to sell you new devices, when you + * will add new protocol to your host, f.e. IPv6 8) + * + * CHECKSUM_UNNECESSARY is applicable to following protocols: + * TCP: IPv6 and IPv4. + * UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a + * zero UDP checksum for either IPv4 or IPv6, the networking stack + * may perform further validation in this case. + * GRE: only if the checksum is present in the header. + * SCTP: indicates the CRC in SCTP header has been validated. + * + * skb->csum_level indicates the number of consecutive checksums found in + * the packet minus one that have been verified as CHECKSUM_UNNECESSARY. + * For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet + * and a device is able to verify the checksums for UDP (possibly zero), + * GRE (checksum flag is set), and TCP-- skb->csum_level would be set to + * two. If the device were only able to verify the UDP checksum and not + * GRE, either because it doesn't support GRE checksum of because GRE + * checksum is bad, skb->csum_level would be set to zero (TCP checksum is + * not considered in this case). * * CHECKSUM_COMPLETE: * @@ -112,6 +130,9 @@ #define CHECKSUM_COMPLETE 2 #define CHECKSUM_PARTIAL 3 +/* Maximum value in skb->csum_level */ +#define SKB_MAX_CSUM_LEVEL 3 + #define SKB_DATA_ALIGN(X) ALIGN(X, SMP_CACHE_BYTES) #define SKB_WITH_OVERHEAD(X) \ ((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))) @@ -571,11 +592,7 @@ struct sk_buff { __u8 wifi_acked:1; __u8 no_fcs:1; __u8 head_frag:1; - /* Encapsulation protocol and NIC drivers should use - * this flag to indicate to each other if the skb contains - * encapsulated packet or not and maybe use the inner packet - * headers if needed - */ + /* Indicates the inner headers are valid in the skbuff. */ __u8 encapsulation:1; __u8 encap_hdr_csum:1; __u8 csum_valid:1; @@ -599,7 +616,8 @@ struct sk_buff { }; kmemcheck_bitfield_begin(flags3); - /* 16 bit hole */ + __u8 csum_level:2; + /* 14 bit hole */ kmemcheck_bitfield_end(flags3); __be16 inner_protocol; @@ -1866,18 +1884,6 @@ static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len) return pskb_may_pull(skb, skb_network_offset(skb) + len); } -static inline void skb_pop_rcv_encapsulation(struct sk_buff *skb) -{ - /* Only continue with checksum unnecessary if device indicated - * it is valid across encapsulation (skb->encapsulation was set). - */ - if (skb->ip_summed == CHECKSUM_UNNECESSARY && !skb->encapsulation) - skb->ip_summed = CHECKSUM_NONE; - - skb->encapsulation = 0; - skb->csum_valid = 0; -} - /* * CPUs often take a performance hit when accessing unaligned memory * locations. The actual performance hit varies, it can be small if the @@ -2798,6 +2804,27 @@ static inline __sum16 skb_checksum_complete(struct sk_buff *skb) 0 : __skb_checksum_complete(skb); } +static inline void __skb_decr_checksum_unnecessary(struct sk_buff *skb) +{ + if (skb->ip_summed == CHECKSUM_UNNECESSARY) { + if (skb->csum_level == 0) + skb->ip_summed = CHECKSUM_NONE; + else + skb->csum_level--; + } +} + +static inline void __skb_incr_checksum_unnecessary(struct sk_buff *skb) +{ + if (skb->ip_summed == CHECKSUM_UNNECESSARY) { + if (skb->csum_level < SKB_MAX_CSUM_LEVEL) + skb->csum_level++; + } else if (skb->ip_summed == CHECKSUM_NONE) { + skb->ip_summed = CHECKSUM_UNNECESSARY; + skb->csum_level = 0; + } +} + /* Check if we need to perform checksum complete validation. * * Returns true if checksum complete is needed, false otherwise @@ -2809,6 +2836,7 @@ static inline bool __skb_checksum_validate_needed(struct sk_buff *skb, { if (skb_csum_unnecessary(skb) || (zero_okay && !check)) { skb->csum_valid = 1; + __skb_decr_checksum_unnecessary(skb); return false; } -- cgit