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net: Clarification of CHECKSUM_UNNECESSARY

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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 <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Herbert 2014-08-27 21:26:46 -07:00 committed by David S. Miller
parent de20fe8e2c
commit 77cffe23c1
3 changed files with 51 additions and 26 deletions
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2
drivers/net/vxlan.c
View File

@ -1158,8 +1158,6 @@ static int vxlan_udp_encap_recv(struct sock *sk, struct sk_buff *skb)
if (!vs)
goto drop;
skb_pop_rcv_encapsulation(skb);
vs->rcv(vs, skb, vxh->vx_vni);
return 0;

74
include/linux/skbuff.h
View File

@ -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;
}

1
net/ipv4/gre_demux.c
View File

@ -125,7 +125,6 @@ static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
*csum_err = true;
return -EINVAL;
}
skb_pop_rcv_encapsulation(skb);
options++;
}