Re: [Qemu-devel] [PATCH v2 00/17] blockdev-add QMP command

[Kevin Wolf <kwolf@redhat.com>]

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.

Kevin