Re: [PATCH net-next v3] net-loopback: set lo dev initial state to UP

On Tue, 9 Feb 2021 11:18:05 -0800 Mahesh Bandewar (महेश बंडेवार) wrote:

On Tue, Feb 9, 2021 at 11:04 AM Jakub Kicinski [off-list ref] wrote:

quoted

On Tue, 9 Feb 2021 10:49:23 -0800 Mahesh Bandewar (महेश बंडेवार) wrote:  

quoted

On Tue, Feb 9, 2021 at 8:23 AM Jakub Kicinski [off-list ref] wrote:  

quoted

On Tue, 9 Feb 2021 12:54:59 +0100 Petr Machata wrote:  

quoted

This will break user scripts, and it fact breaks kernel's very own
selftest. We currently have this internally:

    diff --git a/tools/testing/selftests/net/fib_nexthops.sh b/tools/testing/selftests/net/fib_nexthops.sh
    index 4c7d33618437..bf8ed24ab3ba 100755
    --- a/tools/testing/selftests/net/fib_nexthops.sh
    +++ b/tools/testing/selftests/net/fib_nexthops.sh
    @@ -121,8 +121,6 @@ create_ns()
      set -e
      ip netns add ${n}
      ip netns set ${n} $((nsid++))
    - ip -netns ${n} addr add 127.0.0.1/8 dev lo
    - ip -netns ${n} link set lo up

      ip netns exec ${n} sysctl -qw net.ipv4.ip_forward=1
      ip netns exec ${n} sysctl -qw net.ipv4.fib_multipath_use_neigh=1

This now fails because the ip commands are run within a "set -e" block,
and kernel rejects addition of a duplicate address.  

Thanks for the report, could you send a revert with this explanation?  

Rather than revert, shouldn't we just fix the self-test in that regard?  

The selftest is just a messenger. We all know Linus's stand on
regressions, IMO we can't make an honest argument that the change
does not break user space after it broke our own selftest. Maybe
others disagree..  

Actually that was the reason behind encompassing this behavior change
with a sysctl.

Which as I explained to you is pointless for portable applications.