net: more accurate checksumming in validate_xmit_skb()

skb_csum_hwoffload_help() uses netdev features and skb->csum_not_inet to
determine if skb needs software computation of Internet Checksum or crc32c
(or nothing, if this computation can be done by the hardware). Use it in
place of skb_checksum_help() in validate_xmit_skb() to avoid corruption
of non-GSO SCTP packets having skb->ip_summed equal to CHECKSUM_PARTIAL.

While at it, remove references to skb_csum_off_chk* functions, since they
are not present anymore in Linux  _ see commit cf53b1da73bd ("Revert
 "net: Add driver helper functions to determine checksum offloadability"").

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 4 deletions

diff --git a/Documentation/networking/checksum-offloads.txt b/Documentation/networking/checksum-offloads.txt
index 56e36861245f..d52d191bbb0c 100644
--- a/Documentation/networking/checksum-offloads.txt
+++ b/Documentation/networking/checksum-offloads.txt
@@ -35,6 +35,9 @@ This interface only allows a single checksum to be offloaded.  Where
  encapsulation is used, the packet may have multiple checksum fields in
  different header layers, and the rest will have to be handled by another
  mechanism such as LCO or RCO.
+CRC32c can also be offloaded using this interface, by means of filling
+ skb->csum_start and skb->csum_offset as described above, and setting
+ skb->csum_not_inet: see skbuff.h comment (section 'D') for more details.
 No offloading of the IP header checksum is performed; it is always done in
  software.  This is OK because when we build the IP header, we obviously
  have it in cache, so summing it isn't expensive.  It's also rather short.
@@ -49,9 +52,9 @@ A driver declares its offload capabilities in netdev->hw_features; see
  and csum_offset given in the SKB; if it tries to deduce these itself in
  hardware (as some NICs do) the driver should check that the values in the
  SKB match those which the hardware will deduce, and if not, fall back to
- checksumming in software instead (with skb_checksum_help or one of the
- skb_csum_off_chk* functions as mentioned in include/linux/skbuff.h).  This
- is a pain, but that's what you get when hardware tries to be clever.
+ checksumming in software instead (with skb_csum_hwoffload_help() or one of
+ the skb_checksum_help() / skb_crc32c_csum_help functions, as mentioned in
+ include/linux/skbuff.h).
 
 The stack should, for the most part, assume that checksum offload is
  supported by the underlying device.  The only place that should check is
@@ -60,7 +63,7 @@ The stack should, for the most part, assume that checksum offload is
  may include other offloads besides TX Checksum Offload) and, if they are
  not supported or enabled on the device (determined by netdev->features),
  performs the corresponding offload in software.  In the case of TX
- Checksum Offload, that means calling skb_checksum_help(skb).
+ Checksum Offload, that means calling skb_csum_hwoffload_help(skb, features).
 
 
 LCO: Local Checksum Offload