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.
Peter