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