[Bug 1720126] [NEW] [ip link] Message truncated error for large number of passthrough VFs

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Monique van den Berg (mvandenberg):

[Impact]

When querying a Physical Function netdev with a large amount of VF's
(more than 30), the resulting return message can overflow the 16K
netlink message buffer.

This can be fixed by enabling message peeking on the socket and resizing
the buffer on receive, or by simply enlarging the receive buffer.

Since there's an upper limit to the number of VF's per PF, it's
relatively sane to just enlarge the receive buffer. Please see the
attached patch.

[Test Case]

# Set up 60 VF's on an SR-IOV device
ip link show > /dev/null

Observe the following:
Message truncated
Message truncated
Message truncated

[Regression Potential]

1) Applications relying on the broken behaviour will need to be updated, but it would be a really dubious use case.
2) Increasing the rx buffer size increases the memory footprint (but realistically, this is tiny).
3) Extra processing time is now needed to parse the larger buffer, in the case that a call to "ip link" is on the critical time path of an application, (called multiple times in a tight loop, for example), it would affect load.

[Other Info]

Observed on Ubuntu kernel 4.4.0-93-generic on both 14.04 and 16.04

=====================================================================================================
Ubuntu16 system

stack at cluster04:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.3 LTS
Release:	16.04
Codename:	xenial

stack at cluster04:~$ uname -r
4.4.0-93-generic

stack at cluster04:~$ apt-cache policy iproute2
iproute2:
  Installed: 4.3.0-1ubuntu3.16.04.1
Version table:
*** 4.3.0-1ubuntu3.16.04.1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
=================================================================================================

Ubuntu14 system:
root at boomslang:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 14.04.3 LTS
Release:	14.04
Codename:	trusty

root at boomslang:~# uname -r
4.4.0-96-generic

root at boomslang:~# apt-cache policy iproute2
iproute2:
  Installed: 3.12.0-2ubuntu1
  Version table:
 *** 3.12.0-2ubuntu1 0
        500 http://za.archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages

** Affects: iproute2 (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: iproute2 (CentOS)
     Importance: Unknown
         Status: Unknown


** Tags: patch
-- 
[ip link] Message truncated error for large number of passthrough VFs
https://bugs.launchpad.net/bugs/1720126
You received this bug notification because you are a member of Ubuntu Sponsors Team, which is subscribed to the bug report.