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Re: [Qemu-block] [PATCH v2 3/6] qapi: add nbd-server-remove

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH v2 3/6] qapi: add nbd-server-remove
Date: Wed, 17 Jan 2018 10:03:36 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 01/17/2018 09:51 AM, Vladimir Sementsov-Ogievskiy wrote:

>>> I have a script (for managing libvirt guest, but it can be adopted for
>>> qemu or even used for qemu monitor), which allows
>>> me run qmp commands on vms as easy as:
>>> |qmp VMNAME query-block-jobs or qmp VMNAME nbd-server-remove name exp1
>>> mode hard or even |
>>> |qmp VMNAME blockdev-add id disk driver qcow2 cache {writeback true
>>> direct true} aio native discard unmap file {driver file filename
>>> /tmp/somedisk} |||
>> Yeah, there are various scripting solutions around QMP that can make it
>> easier; but HMP is often still an easy front-line interface for
>> experiments.
> isn't it because these solutions are not available directly in monitor,
> when HMP is?

QMP can be directly accessed in a monitor; it just requires more typing.
 If you are developing QMP commands, it may be easier to use
./scripts/qmp/qmp-shell (couple it with a readline wrapper, and you can
even get tab-completion and history across sessions).  There's also
things like libvirt's 'virsh qmp-monitor-command' for shell-scripting
access to arbitrary QMP commands, provided your guest is run by libvirt.

> may be, we need third type of monitor HQMP which is QMP with simplified
> syntax? Or
> allow qmp commands in simplified syntax directly in HMP?

No, I don't think we need either thing.  Wrappers around existing
monitors is better than bloating qemu proper with a third flavor of
monitor.  And HMP is for humans, with no restrictions on back-compat
changes, so if it doesn't do something you want for quick-and-dirty
testing, you can either add a new HMP command, or just use QMP (or one
of its wrappers, like qmp-shell) in the first place.  Ultimately, our
long-term concern is only about the QMP interface; HMP is supposed to be
convenient.  So if it starts costing too much time to port a QMP
interface to HMP, then don't worry about it.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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