Re: [Qemu-devel] format=raw,readonly errors

[Carl Karsten]

On Mon, May 8, 2017 at 10:32 AM, John Snow <address@hidden> wrote:

>
>
> On 05/08/2017 10:15 AM, Carl Karsten wrote:
> > On Mon, May 8, 2017 at 3:51 AM, Markus Armbruster <address@hidden>
> wrote:
> >
> >> Carl Karsten <address@hidden> writes:
> >>
> >>> address@hidden:~/temp$ qemu-system-x86_64 -m 256 -display curses  -drive
> >>> file=disk.cow -drive file=boot.img
> >>> WARNING: Image format was not specified for 'boot.img' and probing
> >> guessed
> >>> raw.
> >>>          Automatically detecting the format is dangerous for raw
> images,
> >>> write operations on block 0 will be restricted.
> >>>          Specify the 'raw' format explicitly to remove the
> restrictions.
> >>>
> >>> This is OK, as I don't want anything writing to that thing anyway.  So
> to
> >>> get rid of the waring:
> >>>
> >>> address@hidden:~/temp$ qemu-system-x86_64 -drive
> >>> file=boot.img,format=raw,readonly qemu-system-x86_64: Can't use a
> >> read-only
> >>> drive
> >>> qemu-system-x86_64: Initialization of device ide-hd failed: Device
> >>> initialization failed.
> >>
> >> -drive without if=... creates an IDE disk[*].  IDE disks can't do
> >> read-only.  Have you tried omitting ",readonly"?
> >>
> >
> >
> > omitting works, but my goal was for the drive to be read only.
> >
> >
>
> I don't think there's a way to make physical IDE drives "read only." I
> don't think there's any jumper settings or any of the like which can
> accomplish this.
>
> Unlike floppy disks (which you could notch the corner of) or SD cards
> (which have the write lock), I don't think ATA disks have a method for
> being "read only," so this isn't a feature QEMU can support.
>
> What you CAN do, however, is to use -snapshot or otherwise use something
> like a qcow2 overlay to trap all writes to a temporary file that you can
> discard at a later point in time, effectively keeping your original
> image "read only."
>
> I believe that SCSI disks support a read-only mode, though.
>


k - that all makes sense.

kinda ;)

 "write operations on block 0 will be restricted."

Is there a way to explicitly enable that?

The installer on the usb stick keeps stepping on itself rendering it
broken, both physical usb drive and a dd image.

I can play with OS permissions too, but that restricted warning made me
think that would be 'best'.

but but, now that I have index/bootindex working I probably won't be
trashing my installer any more, so non-issue.



-- 
Carl K