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Re: [Qemu-devel] [PATCH v2 00/17] blockdev-add QMP command
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2 00/17] blockdev-add QMP command |
Date: |
Tue, 01 Oct 2013 09:54:40 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
On 10/01/2013 09:50 AM, Kevin Wolf wrote:
> Am 01.10.2013 um 17:41 hat Eric Blake geschrieben:
>> On 10/01/2013 07:20 AM, Kevin Wolf wrote:
>>> This series adds a blockdev-add QMP command and a row of cleanup patches to
>>> separate legacy -drive/drive_add behaviour from blockdev_init() to the
>>> wrapper
>>> function drive_init().
>>>
>>> v2:
>>>
>>> - Removed I/O throttling and copy-on-read options from the schema: Both are
>>> candidates for becoming block filters instead. For the time being, you can
>>> use the existing QMP commands in order to enable I/O throttling on a
>>> device
>>> created with blockdev-add in a second step.
>>
>> Tolerable as a stop-gap; but doesn't that mean that there is a window
>> where throttling is not active? Anything that can restrict block
>> operations must ultimately be specified atomically up front to avoid a
>> non-deterministic burst during the race window. But in the interest of
>> incremental improvements, I can live with the approach used here, while
>> still waiting for throttling to be implemented as a true filter device.
>
> Immediately after blockdev-add, the block device is still completely
> unused. You can set the throttling options before you do the
> corresponding device-add or block job command or whatever you're
> planning to do with the device.
Ah. So there's no race window after all. Good to know.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCH v2 08/17] blockdev: Move parsing of 'if' option to drive_init, (continued)