[PATCH v2 00/14] Clean up checksum and header generation for inbound packets

[David Gibson <david@gibson.dropbear.id.au>]

The main packet "fast paths" for UDP and TCP mostly just forward
packets rather than generating them from scratch.  However the control
paths for ICMP and DHCP sometimes generate packets more or less from
scratch.  Because these are relatively rare, it's not performance
critical.

The paths for sending these packets have some duplication of the
header generation.  There's also some layering violation in
tap_ip_send() which both generates IP headers and updates the L4 (UDP
or UCMP) checksum.

Finally that checksum generation is a little awkward: it temporarily
generates the IP pseudo header (or something close enough to serve) in
the place of the actual header, generates the checksum, then replaces
it with the real IP header.  This approach seems to be causing
miscompiles with some LTO optimization, because the stores to the
pseudo header are being moved or elided across the code calculating
the checksum.

This series addresses all of these.  We consolidate and clarify the
packet sending helpers, and use them in some places there was
previously duplicated code.  In the process we use new checksum
generation helpers which take a different approach which should avoid
the LTO problems (this aspect I haven't tested yet though).

Changes since v1:
 * Numerous minor style changes
 * Rename header generation helpers to make their behaviour clearer
 * Added several missing function doc comments
 * Corrected some erroneous statements and terms in comments

David Gibson (14):
  Add csum_icmp6() helper for calculating ICMPv6 checksums
  Add csum_icmp4() helper for calculating ICMP checksums
  Add csum_udp6() helper for calculating UDP over IPv6 checksums
  Add csum_udp4() helper for calculating UDP over IPv4 checksums
  Add csum_ip4_header() helper to calculate IPv4 header checksums
  Add helpers for normal inbound packet destination addresses
  Remove support for TCP packets from tap_ip_send()
  tap: Remove unhelpeful vnet_pre optimization from tap_send()
  Split tap_ip_send() into IPv4 and IPv6 specific functions
  tap: Split tap_ip6_send() into UDP and ICMP variants
  ndp: Remove unneeded eh_source parameter
  ndp: Use tap_icmp6_send() helper
  tap: Split tap_ip4_send() into UDP and ICMP variants
  dhcp: Use tap_udp4_send() helper in dhcp()

 arp.c      |   2 +-
 checksum.c | 120 ++++++++++++++++-----
 checksum.h |  15 ++-
 dhcp.c     |  19 +---
 dhcpv6.c   |  21 +---
 icmp.c     |  12 +--
 ndp.c      |  28 +----
 ndp.h      |   3 +-
 tap.c      | 312 ++++++++++++++++++++++++++++++++++-------------------
 tap.h      |  19 +++-
 10 files changed, 345 insertions(+), 206 deletions(-)

-- 
2.37.3