Re: kern/53562: bridge(4) breaks segmentation / TX checksum offloading

[Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>]

The following reply was made to PR kern/53562; it has been noted by GNATS.

From: Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>
To: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%NetBSD.org@localhost>
Cc: 
Subject: Re: kern/53562: bridge(4) breaks segmentation / TX checksum
 offloading
Date: Tue, 4 Dec 2018 09:32:45 +0900

 First, let me summarize the current status of the problem. Most problems
 have been resolved by msaito. The remaining problem is that transmission
 from interface if0 to interface if1 fails when any TX offload option is
 enabled for if0 but disabled for if1.
 
 We need handle TX offload in software in bridge_output() when some TX
 offload option is enabled for a packet and it is not available for the
 destination interface. The attached patches deal with this as follows.
 
 For unicast:
 
 (1) When the destination interface is the same as source interface, we
      do not need to handle offload options; send a packet as is.
 
 (2) When the destination is different from the source, check whether TX
      offload options specified in a packet is supported by the
      destination. If so, we can send it as is. Otherwise, handle these
      options in software.
 
 For multicast/broadcast:
 
 (3) Send a packet as is if all the members of that bridge support given
      TX offload options. Otherwise, handle these options in software.
 
 For (3) we need calculate logical AND b/w capabilities of TX offload
 options in member interface (ifp->if_csum_flags_tx). I've added
 sc_csum_flags_tx flag to bridge softc for this purpose. This flag is
 updated when a member is (i) added to or (ii) removed from a bridge, or
 (iii) if_csum_flags_tx flag of a member interface is manipulated via
 ifconfig(8).
 
 Also, currently, if_csum_flags_tx do not contains M_CSUM_TSOv[46]. I've
 added these flags when TSOv[46] is enabled for that interface. As far
 as I can see, no one seems to depend on the old behavior.
 
 I've separated the patch into four parts for readability.
 
 (a) http://www.netbsd.org/~rin/bridge_20181204/ether_sw_offload_20181204.patch
 
 This patch provides routines to handle TX/RX offload options in software
 for ethernet. Since this breaks separation between L2 and L3/L4, I've
 added new files (ether_sw_offload.[ch]) rather than adding the routines
 to existing files.
 
 (b) http://www.netbsd.org/~rin/bridge_20181204/bridge_sw_offload_20181204.patch
 
 This is main patch to deal with the problem described above by using (a).
 
 (c) http://www.netbsd.org/~rin/bridge_20181204/if_shmem_sw_offload_20181204.patch
 
 This patch adds TX/RX offload support for shmemif(4) using (a). This may
 be useful for testing offload related codes in the ATF framework. This
 patch also contains a test code written by msaito; if_capabilities for
 shmemif(4) can be specified by environmental variable
 RUMP_SHMIF_CAPENABLE:
 
    setenv RUMP_SHMIF_CAPENABLE 0x7ff80 (all offload)
    setenv RUMP_SHMIF_CAPENABLE 0x6aa80 (all TX)
    setenv RUMP_SHMIF_CAPENABLE 0x15500 (all RX)
 
 for definition of flags, see sys/net/if.h:
 
    https://nxr.netbsd.org/xref/src/sys/net/if.h#591
 
 I've tested all tests in /usr/tests passed with all offload options
 enabled (RUMP_SHMIF_CAPENABLE=0x7ff80).
 
 (d) http://www.netbsd.org/~rin/bridge_20181204/simplify_ip_output_20181204.patch
 
 This patch simplify logics in ip{,6}_output() by using M_CSUM_TSOv[46]
 bits in ifp->if_csum_flags_tx.
 
 Any comments and suggestions are welcomed. I thank msaito for fruitful
 discussion!
 
 rin