Re: [Qemu-devel] PATCH: v3 Allow control over drive file open mode

[Jamie Lokier <jamie@shareable.org>]

Daniel P. Berrange wrote:
> On Fri, Aug 01, 2008 at 10:10:09AM -0500, Anthony Liguori wrote:
> > Daniel P. Berrange wrote:
> > >This is version 3 of the patch.
> > >  
> > 
> > Allowing the user to specify what mode we use to open a file is IMHO not 
> > a good interface for a user.  A user should only be concerned with how 
> > we expose a disk to the guest, not the underlying implementation of how 
> > we support this.  It has subtle side-effects that a user is not going to 
> > expect unless they are intimately familiar with how QEMU is implemented 
> > (like snapshotting breaking).
> 
> So if I'm understanding you correctly, you'd be OK with a mode=ro, which 
> would make the emulated drive itself read-only - independant of what 
> open() flags we use for opening the file on the host ?  
> 
> So my next question would be, what IDE / SCSI / USB drives have a
> concept of 'read only' ? A CDROM clearly is clearly readonly, and
> floppy disks probably be to but can you mark general disks as read
> only ?

Many USB drives do have a little switch.  USB drives use the SCSI
protocol, so SCSI is sort of covered.

They aren't as common but there are read-only IDE interfaces out
there, for phorensic disk reading.

-- Jamie