Re: [PATCH 0/2] keepalive default

[Eric Blake]

On 7/9/20 3:35 AM, Daniel P. Berrangé wrote:
> On Wed, Jul 08, 2020 at 10:15:37PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > Hi all!
> >
> > We understood, that keepalive is almost superfluous with default 2 hours
> > in /proc/tcp_keepalive_time. Forcing user to setup keepalive for the
> > whole system doesn't seem right, better setup it per-socket.
>
> Adding the ability to explicitly configure the keepalive settings makes
> sense for QEMU. Completely ignoring system defaults when no explicit
> settings are given though is not valid IMHO.

We already have the ability to add per-socket keepalive (see commit 
aec21d3175, in 4.2).  I guess what you are trying to further do is 
determine whether the default value for that field, when not explicitly 
specified by the user, can have saner semantics (default off for chardev 
sockets, default on for nbd clients where retry was enabled).  But since 
you already have to explicitly opt-in to nbd retry, what's so hard about 
opting in to keepalive at the same time, other than more typing?  Given 
that the easiest way to do this is via a machine-coded generation of the 
command line or QMP command, it doesn't seem that hard to just keep 
things as they are with explicit opt-in to per-socket keepalive.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org