Am 07.03.2013 um 09:56 hat Peter Lieven geschrieben: > On 07.03.2013 09:50, Kevin Wolf wrote: > >Am 06.03.2013 um 21:39 hat Paolo Bonzini geschrieben: > >>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. > > > >What semantics would the both operations have? Is truncate the same as > >it used to be? I don't really understand what "revalidate" would do, it > >sounds like a read-only operation from its name? > > > >>>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. > > > >This is probably right. > > If bs->growable is 1 for all drivers, whats the fix status of CVE-2008-0928? > This > flag was introduced as a fix for this problem. > > bdrv_check_byte_request() does nothing useful if bs->growable is 1.
Don't ignore the difference between bdrv_open() and bdrv_file_open(). Typically you have two BDSes: On top there is e.g. a qcow2 BDS that is opened through bdrv_open() and has bs->growable = false. Its bs->file is using the file protocol (raw-posix driver) and opened by bdrv_file_open(). This one has bs->file->growable = true so that qcow2 can write to newly allocated areas without calling bdrv_truncate() first. Kevin
