Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking

[Kevin Wolf]

Am 07.03.2013 um 10:25 hat Peter Lieven geschrieben:
> 
> Am 07.03.2013 um 10:22 schrieb Kevin Wolf <address@hidden>:
> 
> > Am 07.03.2013 um 10:16 hat Peter Lieven geschrieben:
> >>>> 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.
> >> 
> >> Sorry, I have to admin I am little confused by what is happening in 
> >> bdrv_open().
> >> 
> >> However, what I can say is that bs->growable is 1 for an iSCSI backed
> >> harddrive and I wonder how this can happen if bdrv_file_open is not used 
> >> for
> >> opening it because that is the only place where bs->growable is set to 1.
> >> 
> >> cmdline:
> >> x86_64-softmmu/qemu-system-x86_64 -k de -enable-kvm -m 1024 -drive 
> >> if=virtio,file=iscsi://172.21.200.31/iqn.2001-05.com.equallogic:0-8a0906-16470e107-713001aa6de511e0-001-test/0
> >>  -vnc :1 -boot dc -monitor stdio
> > 
> > It is used for the iscsi driver. You have a raw BDS (growable == false)
> > on top of an iscsi one (growable == true).
> 
> Ok, but growable == true is wrong for the iSCSI driver isn`t it?

I guess it depends on your definition. If you say that growable includes
the capability of growing the image, then yes, it's wrong. If you only
interpret it as permission to write beyond EOF (if the driver supports
that), then it's right even though any such attempt will result in an
error.

Practically speaking, the difference is between -EIO returned from
bdrv_check_byte_request() and -EIO from iscsi_aio_write16_cb(), i.e.
the result is the same.

Kevin