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Message-ID: <3865908.1586874010@warthog.procyon.org.uk>
Date: Tue, 14 Apr 2020 15:20:10 +0100
From: David Howells <dhowells@...hat.com>
To: linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
linux-afs@...ts.infradead.org, ceph-devel@...r.kernel.org
cc: dhowells@...hat.com, keyrings@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
fweimer@...hat.com
Subject: What's a good default TTL for DNS keys in the kernel
Since key.dns_resolver isn't given a TTL for the address information obtained
for getaddrinfo(), no expiry is set on dns_resolver keys in the kernel for
NFS, CIFS or Ceph. AFS gets one if it looks up a cell SRV or AFSDB record
because that is looked up in the DNS directly, but it doesn't look up A or
AAAA records, so doesn't get an expiry for the addresses themselves.
I've previously asked the libc folks if there's a way to get this information
exposed in struct addrinfo, but I don't think that ended up going anywhere -
and, in any case, would take a few years to work through the system.
For the moment, I think I should put a default on any dns_resolver keys and
have it applied either by the kernel (configurable with a /proc/sys/ setting)
or by the key.dnf_resolver program (configurable with an /etc file).
Any suggestion as to the preferred default TTL? 10 minutes?
David
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