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

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

Agreed then, will make the change.


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