From: Jonathan Morton <chromatix99@gmail.com>
To: "Rodney W. Grimes" <4bone@gndrsh.dnsmgr.net>
Cc: Dave Taht <dave.taht@gmail.com>,
ECN-Sane <ecn-sane@lists.bufferbloat.net>
Subject: Re: [Ecn-sane] Fwd: [PATCH net] ipv4: Ignore ECN bits for fib lookups in fib_compute_spec_dst()
Date: Tue, 29 Dec 2020 22:59:23 +0200 [thread overview]
Message-ID: <25865485-3505-49F7-ACE4-8F13B43BC54E@gmail.com> (raw)
In-Reply-To: <202012292013.0BTKDGCk078796@gndrsh.dnsmgr.net>
> On 29 Dec, 2020, at 10:13 pm, Rodney W. Grimes <4bone@gndrsh.dnsmgr.net> wrote:
>
> If these are purely kernel macros that scope of work is well contained. Are these macro's exported from a header to userland visible code?
It appears RT_TOS is defined in a "uapi" header, that is, Userspace API. So yes, and this also means any bugs in it have propagated into userspace code built against it.
Actually, it looks like it is not a bug in the macro itself, but in its intended application, referring to an obsolete and very short-lived specification. It's extracting *specifically* the widened Type of Service bitfield, containing the non-orthogonal "flags" indicating Max Throughput, Min Latency, Max Reliability, and Min Cost (this last being the short-lived part of the spec, as Diffserv and ECN replaced it very quickly). The mask specifically excludes the Precedence field and thus the most-significant half of the Diffserv field.
- Jonathan Morton
prev parent reply other threads:[~2020-12-29 20:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <49ff39b1f55c914847cd58678bae6282112db701.1608836260.git.gnault@redhat.com>
2020-12-29 3:18 ` Dave Taht
2020-12-29 13:33 ` Rodney W. Grimes
2020-12-29 15:21 ` Jonathan Morton
2020-12-29 20:13 ` Rodney W. Grimes
2020-12-29 20:59 ` Jonathan Morton [this message]
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