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Re: [Qemu-devel] [PATCH] ide: refuse WIN_READ_NATIVE_MAX on empty device
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] ide: refuse WIN_READ_NATIVE_MAX on empty device |
Date: |
Fri, 5 Apr 2013 14:19:41 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, Apr 05, 2013 at 12:56:07PM +0200, Markus Armbruster wrote:
> Stefan Hajnoczi <address@hidden> writes:
>
> > What is the highest addressable sector on an empty CD-ROM? Nothing is
> > addressable so produce an error.
> >
> > This patch prevents a divide-by-zero in ide_set_sector() since
> > s->sectors and s->heads would be 0. Not to mention that a sector=-1
> > argument would be nonsense.
> >
> > Note that WIN_READ_NATIVE_MAX can be triggered using hdparm -N 1024
> > /dev/cdrom. The LBA bit will be set to 1 though, so the only easy way
> > to go down the ide_set_sector() CHS code path which divides by zero is
> > to comment out the s->select & 0x40 case for testing.
>
> Suggests you did that.
>
> Have you tried the reproducer with a physical drive? Does it fail the
> command when empty, too?
Believe it or not, I don't have access to an ATAPI CD-ROM drive. Would
you be able to try out hdparm -N 1024 /dev/cdrom?
Note that READ NATIVE MAX is optional, real drives may not implement it
since it seems geared towards the Host Protected Area feature which
makes no sense on CD-ROMs. (The idea is a reserved area on the disk
where system data can be stored and the OS will not touch it.)
Stefan
Re: [Qemu-devel] [PATCH] ide: refuse WIN_READ_NATIVE_MAX on empty device, Stefan Hajnoczi, 2013/04/10