Re: [PATCH] net: dev_forward_skb(): Scrub packet's per-netns info only when crossing netns

----- shmulik.ladkani@gmail.com wrote:

On Thu, 15 Mar 2018 09:35:51 -0700 (PDT) Liran Alon
[off-list ref] wrote:

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----- shmulik.ladkani@gmail.com wrote:

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On Thu, 15 Mar 2018 08:01:03 -0700 (PDT) Liran Alon
[off-list ref] wrote:  

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I still think that default behavior should be to zero skb->mark

only  

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when skb  

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cross netdevs in different netns.  

But the previous default was scrub the mark in *both* xnet and
non-xnet
situations.

Therefore, there might be users which RELY on this (strange)

default

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behavior in their same-netns-veth-pair setups.
Meaning, changing the default behavior might break their apps

relying

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on
the former default behavior.

This is why the "disable mark scrubbing in non-xnet case" should

be

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opt-in.  

We think the same.
The only difference is that I think this for now should be

controllable

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by a global /proc/sys/net/core file instead of giving a flexible

per-netdev

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control.
Because that is a larger change that could be done later.

A flags attribute to veth newlink is a very scoped change.
User controls this per veth creation.
This is way more neat than /proc/sys/net and provides the desired
granular
control.

Also, scoping this to veth has the advantage of not affecting the many
other
dev_forward_skb callers.

Agreed. But isn't this an issue also for the
many others (& future) callers of dev_forward_skb()?
This seems problematic to me.

This will kinda leave a kernel interface with broken default behavior
for backwards comparability.

A flag to netdev or /proc/sys/net/core to "fix" default behavior
will avoid this.

Regards,
Shmulik