Am 07.03.2013 um 09:53 hat Peter Lieven geschrieben: > On 06.03.2013 21:39, Paolo Bonzini wrote: > >Il 06/03/2013 20:03, Peter Lieven ha scritto: > >>Am 06.03.2013 19:48, schrieb Jeff Cody: > >>>On Wed, Mar 06, 2013 at 07:31:51PM +0100, Paolo Bonzini wrote: > >>>>Il 06/03/2013 19:14, Jeff Cody ha scritto: > >>>>>QCOW breaks with it using a normal raw posix file as a device. As a > >>>>>test: qemu-img create -f qcow test.qcow 5G. Now run qemu with that > >>>>>drive mounted, and try to partition and format it. QEMU now asserts. > >>>>> > >>>>>The nicety of being able to using truncate during a write call, > >>>>>especially for VHDX (which can have relatively large block/cluster > >>>>>sizes), so to grow the file sparsely in a dynamically allocated file. > >>>> > >>>>Perhaps we need two APIs, "truncate" and "revalidate". > >>>> > >>>>Truncate should be a no-op if (!bs->growable). > >>>> > >>>>Revalidate could be called by the block_resize monitor command with no > >>>>size specified. > >>>> > >>>>Paolo > >>> > >>>I think that is a good solution. Is it better to have "truncate" and > >>>"revalidate", or "truncate" and "grow", with grow being a subset of > >>>truncate, with fewer restrictions? There may still be operations > >>>where it is OK to grow a file, but not OK to shrink it. > >> > >>Or as a first step: > >> > >>a) Call brdv_drain_all() only if the device is shrinked (independently of > >>!bs->growable) > >>b) Call brdv_drain_all() inside iscsi_truncate() because it is a special > >>requirement there > >>c) Fix the value of bs->growable for all drivers > > > >Let's start from (c). bdrv_file_open sets bs->growable = 1. I think it > >should be removed and only the file protocol should set it. > > > >Then we can add bdrv_revalidate and, for block_resize, call > >bdrv_revalidate+bdrv_truncate. For bs->growable = 0 && > >!bs->drv->bdrv_truncate, bdrv_truncate can just check that the actual > >size is the same or bigger as the one requested, and fail otherwise. > > > >Paolo > > > > Regarding brd_drain_all(). Is the fix right to call it only on device shrink? > In this case it has to be added to iscsi_truncate as well.
The real fix would bdrv_drain(bs). I hope we're not too far away from that today, even though we're not quite there. Kevin