[libvirt] [RFC] Add API to change qemu agent response timeout

[Daniel P. Berrangé]

On Thu, Oct 03, 2019 at 04:52:12PM -0500, Jonathon Jongsma wrote:
> Some layered products such as oVirt have requested a way to avoid being
> blocked by guest agent commands when querying a loaded vm. For example,
> many guest agent commands are polled periodically to monitor changes,
> and rather than blocking the calling process, they'd prefer to simply
> time out when an agent query is taking too long.
> 
> This patch adds a way for the user to specify a custom agent timeout
> that is applied to all agent commands.
> 
> One special case to note here is the 'guest-sync' command. 'guest-sync'
> is issued internally prior to calling any other command. (For example,
> when libvirt wants to call 'guest-get-fsinfo', we first call
> 'guest-sync' and then call 'guest-get-fsinfo').
> 
> Previously, the 'guest-sync' command used a 5-second timeout
> (VIR_DOMAIN_QEMU_AGENT_COMMAND_DEFAULT), whereas the actual command that
> followed always blocked indefinitely
> (VIR_DOMAIN_QEMU_AGENT_COMMAND_BLOCK). As part of this patch, if a
> custom timeout is specified that is shorter than
> 5 seconds,  this new timeout also used for 'guest-sync'. If there is no
> custom timeout or if the custom timeout is longer than 5 seconds, we
> will continue to use the 5-second timeout.
> 
> See https://bugzilla.redhat.com/show_bug.cgi?id=1705426 for additional details.
> 
> Signed-off-by: Jonathon Jongsma <jjongsma at redhat.com>
> ---
>  include/libvirt/libvirt-qemu.h |  2 +

For something that is fullfilling a RFE from oVirt, adding an API in
libvirt-qemu.h is not a viable solution.

We class libvirt-qemu.h API usage as unsupported, as it is a
providing a backdoor around libvirt, for dev/test scenarios
only.

For anything that is to be used in production, it has to be
fully supported in the main libvirt API or XML schema.

Regards,
Daniel
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