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

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.