Subject: Re: [PATCH net-next 00/12] Unmask upper DSCP bits - part 2

From: Guillaume Nault <[email-masked]>
Date: Tue, 27 Aug 2024 15:47:05 +0200

On Tue, Aug 27, 2024 at 02:18:01PM +0300, Ido Schimmel wrote:
> tl;dr - This patchset continues to unmask the upper DSCP bits in the
> IPv4 flow key in preparation for allowing IPv4 FIB rules to match on
> DSCP. No functional changes are expected. Part 1 was merged in commit
> ("Merge branch 'unmask-upper-dscp-bits-part-1'").
> 
> The TOS field in the IPv4 flow key ('flowi4_tos') is used during FIB
> lookup to match against the TOS selector in FIB rules and routes.
> 
> It is currently impossible for user space to configure FIB rules that
> match on the DSCP value as the upper DSCP bits are either masked in the
> various call sites that initialize the IPv4 flow key or along the path
> to the FIB core.
> 
> In preparation for adding a DSCP selector to IPv4 and IPv6 FIB rules, we

Hum, do you plan to add a DSCP selector for IPv6? That shouldn't be
necessary as IPv6 already takes all the DSCP bits into account. Also we
don't need to keep any compatibility with the legacy TOS interpretation,
as it has never been defined nor used in IPv6.

> need to make sure the entire DSCP value is present in the IPv4 flow key.
> This patchset continues to unmask the upper DSCP bits, but this time in
> the output route path.