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Re: [RFC PATCH 00/18] Add qemu-storage-daemon
From: |
Stefan Hajnoczi |
Subject: |
Re: [RFC PATCH 00/18] Add qemu-storage-daemon |
Date: |
Tue, 5 Nov 2019 16:52:50 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
On Thu, Oct 17, 2019 at 03:01:46PM +0200, Kevin Wolf wrote:
> This series adds a new tool 'qemu-storage-daemon', which can be used to
> export and perform operations on block devices. There is some overlap
> between qemu-img/qemu-nbd and the new qemu-storage-daemon, but there are
> a few important differences:
>
> * The qemu-storage-daemon has QMP support. The command set is obviously
> restricted compared to the system emulator because there is no guest,
> but all of the block operations are present.
>
> This means that it can access advanced options or operations that the
> qemu-img command line doesn't expose. For example, blockdev-create is
> a lot more powerful than 'qemu-img create', and qemu-storage-daemon
> allows to execute it without starting a guest.
>
> Compared to qemu-nbd it means that, for example, block jobs can now be
> executed on the server side, and backing chains shared by multiple VMs
> can be modified this way.
>
> * The existing tools all have a separately invented one-off syntax for
> the job at hand, which usually comes with restrictions compared to the
> system emulator. qemu-storage-daemon shares the same syntax with the
> system emulator for most options and prefers QAPI based interfaces
> where possible (such as --blockdev), so it should be easy to make use
> of in libvirt.
>
> * While this series implements only NBD exports, the storage daemon is
> intended to serve multiple protocols and its syntax reflects this. In
> the past, we had proposals to add new one-off tools for exporting over
> new protocols like FUSE or TCMU.
>
> With a generic storage daemon, additional export methods have a home
> without adding a new tool for each of them.
No comments on the command-line, QAPI, or monitor aspects, but the
general idea of having a qemu-storage-daemon is likely to be useful.
Acked-by: Stefan Hajnoczi <address@hidden>
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