[libvirt] [libvirt PATCH] qemu: Support discard for disk

[Osier Yang]

On 15/05/13 21:44, Paolo Bonzini wrote:
> Il 15/05/2013 15:17, Daniel P. Berrange ha scritto:
>> On Wed, May 15, 2013 at 02:56:03PM +0200, Paolo Bonzini wrote:
>>> Il 14/05/2013 14:44, Osier Yang ha scritto:
>>>> QEMU introduced "discard" option for drive since commit a9384aff53,
>>>>
>>>> <...>
>>>> @var{discard} is one of "ignore" (or "off") or "unmap" (or "on") and
>>>> controls whether @dfn{discard} (also known as @dfn{trim} or @dfn{unmap})
>>>> requests are ignored or passed to the filesystem.  Some machine types
>>>> may not support discard requests.
>>>> </...>
>>>>
>>>> This patch exposes the support in libvirt.
>>>>
>>>> QEMU supported "discard" for "-drive" since v1.5.0-rc0:
>>> I would prefer to use ignore/unmap instead of off/on in libvirt.
>> If we think there's any chance QEMU might gain a 3rd possible
>> value for this setting, then I tend to agree with you that
>> avoiding off/on would be desirable.
> Yes, the 3rd setting would be "anchor", i.e. when discarding keep any
> preallocation but discard the data.  This corresponds to the XFS ioctl
> XFS_IOC_ZERO_RANGE.
>
Agreed then, will make the change.

Osier