This following message is printed in the console each time a network
device configured with an IPv6 addresses is ready to be used:

  ADDRCONF(NETDEV_CHANGE): <iface>: link becomes ready

When netns are being extensively used -- e.g. by re-creating netns' with
veth to discuss with each others for testing purposes like mptcp_join.sh
selftest does -- it generates a lot of messages like that: more than 700
when executing mptcp_join.sh with the latest version.

It looks like this message is not that helpful after all: maybe it can
be used as a sign to know if there is something wrong, e.g. if a device
is being regularly reconfigured by accident? But even then, there are
better ways to monitor and diagnose such issues.

When looking at commit 3c21edbd1137 ("[IPV6]: Defer IPv6 device
initialization until the link becomes ready.") which introduces this new
message, it seems it had been added to verify that the new feature was
working as expected. It could have then used a lower level than "info"
from the beginning but it was fine like that back then: 17 years ago.

It seems then OK today to simply lower its level, similar to commit
7c62b8dd5ca8 ("net/ipv6: lower the level of "link is not ready" messages")
and as suggested by Mat [1], Stephen and David [2].

Link: https://lore.kernel.org/mptcp/614e76ac-184e-c553-af72-084f792e60b0@kernel.org/T/ [1]
Link: https://lore.kernel.org/netdev/68035bad-b53e-91cb-0e4a-007f27d62b05@tessares.net/T/ [2]
Suggested-by: Mat Martineau <martineau@kernel.org>
Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
Suggested-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
RFC to v1:
- Thanks to Stephen and David's feedback, this new version is smaller
  and simpler: only the level of the problematic message is changed, no
  more sysctl.
- Link to RFC: https://lore.kernel.org/r/20230601-net-next-skip_print_link_becomes_ready-v1-1-c13e64c14095@tessares.net
---
 net/ipv6/addrconf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3797917237d0..5479da08ef40 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3633,8 +3633,8 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 				idev->if_flags |= IF_READY;
 			}
 
-			pr_info("ADDRCONF(NETDEV_CHANGE): %s: link becomes ready\n",
-				dev->name);
+			pr_debug("ADDRCONF(NETDEV_CHANGE): %s: link becomes ready\n",
+				 dev->name);
 
 			run_pending = 1;
 		}

---
base-commit: a395b8d1c7c3a074bfa83b9759a4a11901a295c5
change-id: 20230601-net-next-skip_print_link_becomes_ready-5bc2655daa24

Best regards,
-- 
Matthieu Baerts <matthieu.baerts@tessares.net>

On Fri, 02 Jun 2023 11:36:07 +0200 Matthieu Baerts wrote:
> This following message is printed in the console each time a network
> device configured with an IPv6 addresses is ready to be used:
> 
>   ADDRCONF(NETDEV_CHANGE): <iface>: link becomes ready
> 
> When netns are being extensively used -- e.g. by re-creating netns' with
> veth to discuss with each others for testing purposes like mptcp_join.sh
> selftest does -- it generates a lot of messages like that: more than 700
> when executing mptcp_join.sh with the latest version.
> 
> It looks like this message is not that helpful after all: maybe it can
> be used as a sign to know if there is something wrong, e.g. if a device
> is being regularly reconfigured by accident? But even then, there are
> better ways to monitor and diagnose such issues.
> 
> When looking at commit 3c21edbd1137 ("[IPV6]: Defer IPv6 device
> initialization until the link becomes ready.") which introduces this new
> message, it seems it had been added to verify that the new feature was
> working as expected. It could have then used a lower level than "info"
> from the beginning but it was fine like that back then: 17 years ago.
> 
> It seems then OK today to simply lower its level, similar to commit
> 7c62b8dd5ca8 ("net/ipv6: lower the level of "link is not ready" messages")
> and as suggested by Mat [1], Stephen and David [2].
> 
> Link: https://lore.kernel.org/mptcp/614e76ac-184e-c553-af72-084f792e60b0@kernel.org/T/ [1]
> Link: https://lore.kernel.org/netdev/68035bad-b53e-91cb-0e4a-007f27d62b05@tessares.net/T/ [2]
> Suggested-by: Mat Martineau <martineau@kernel.org>
> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> Suggested-by: David Ahern <dsahern@kernel.org>
> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

This appears to have been applied as commit f69de8aa4752 ("ipv6: lower
"link become ready"'s level message") in net-next, thank you!

On Fri, Jun 2, 2023 at 11:36 AM Matthieu Baerts
<matthieu.baerts@tessares.net> wrote:
>
> This following message is printed in the console each time a network
> device configured with an IPv6 addresses is ready to be used:
>
>   ADDRCONF(NETDEV_CHANGE): <iface>: link becomes ready
>
> When netns are being extensively used -- e.g. by re-creating netns' with
> veth to discuss with each others for testing purposes like mptcp_join.sh
> selftest does -- it generates a lot of messages like that: more than 700
> when executing mptcp_join.sh with the latest version.
>
> It looks like this message is not that helpful after all: maybe it can
> be used as a sign to know if there is something wrong, e.g. if a device
> is being regularly reconfigured by accident? But even then, there are
> better ways to monitor and diagnose such issues.
>
> When looking at commit 3c21edbd1137 ("[IPV6]: Defer IPv6 device
> initialization until the link becomes ready.") which introduces this new
> message, it seems it had been added to verify that the new feature was
> working as expected. It could have then used a lower level than "info"
> from the beginning but it was fine like that back then: 17 years ago.
>
> It seems then OK today to simply lower its level, similar to commit
> 7c62b8dd5ca8 ("net/ipv6: lower the level of "link is not ready" messages")
> and as suggested by Mat [1], Stephen and David [2].
>
> Link: https://lore.kernel.org/mptcp/614e76ac-184e-c553-af72-084f792e60b0@kernel.org/T/ [1]
> Link: https://lore.kernel.org/netdev/68035bad-b53e-91cb-0e4a-007f27d62b05@tessares.net/T/ [2]
> Suggested-by: Mat Martineau <martineau@kernel.org>
> Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
> Suggested-by: David Ahern <dsahern@kernel.org>
> Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
> ---

Reviewed-by: Eric Dumazet <edumazet@google.com>