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

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

From: Rin Okuyama <>
To: Masanobu SAITOH <>, Christoph Badura <>
Cc: Ryota Ozaki <>,
 "" <>,,,
Subject: Re: kern/53562: bridge(4) breaks segmentation / TX checksum
Date: Sat, 8 Sep 2018 08:48:04 +0900

 On 2018/09/07 17:50, Masanobu SAITOH wrote:
 > On 2018/09/06 6:51, Christoph Badura wrote:
 >> On Wed, Sep 05, 2018 at 09:04:16PM +0900, Rin Okuyama wrote:
 >>> With both patches, TX works fine through an interface added to bridge,
 >>> even if TSO is enabled. However, RX from an host which shares the
 >>> interface via bridge does not work for larger packets (because of TSO?).
 >>> RX of smaller packets and TX work for that host.
 >> I would not expect any TSO flags to be set on a packet that is received
 >> from another host.  The packet should have been segmented on other host
 >> already.
 >>> I'm not sure if my setup should work in principle...
 >> Maybe you could describe your setup in more detail.  Looking at the PR I
 >> don't understand what exactly your setup is.
 > I think so, too. I read if_bridge.c and I think ozaki-r's change should be
 > correct. There might be another bug. The detailed configuration is required
 > to reproduce the problem.
 Yeah, sorry for the poor explanation. I'm working on an userland
 application on Raspberry Pi, which emulates an ethernet adapter for
 a client connected via GPIO. Then, it sends and receives packets for
 the client using tap device bridged to a NIC. When TSO is enabled for
 that NIC, the client cannot retrieve file via ftp, for example.
 Well, my setup is hard to reproduce. The following would be a simplest
 example where your patch does not work:
 - NetBSD/amd64-currnet with wm0 connected to LAN
 - qemu-3.0.0nb2 installed from pkgsrc
 - setup tap and bridge as follows:
      # ifconfig tap0 create up
      # ifconfig bridge0 create
      # brconfig bridge0 add wm0 add tap0 up
 - run NetBSD/amd64 8.0 on QEMU with tap enabled:
      # qemu-system-x86_64 -m 128m -cdrom NetBSD-8.0-amd64.iso -boot d \
        -display curses -net tap,fd=3 -net nic 3<>/dev/tap0
 Then, the virtual host can send and receive small packets, e.g.,
 ping works well regardless of whether TSO is enabled or not for wm0.
 However, it cannot receive larger packets when TSO is enabled, e.g.,
 file cannot be retrieved through ftp. If TSO is turned off, everything
 works fine.
 >> It might be worth going over the original PR kern/27007 again.  Also note
 >> the second part of PR kern/21831 by yamt@.
 The second part of kern/21831 still affects at least for tap?
 >> Maybe we need ATF tests.  That certainly would be nice.  Also we now have
 >> more test cases to consider: npf and pf active on the bridge.
 > I think adding offload functions into shmif(4) is a good idea to test offload
 > stuff.
 Well, I'm working on offload engine for shmif(4). The application
 mentioned above emulates TSO and TX/RX checksum offload by software.
 The algorithm, or at least ideas, can be easily applied to shmif(4).

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