Re: [Qemu-devel] [PATCH] ide: refuse WIN_READ_NATIVE_MAX on empty device

[Markus Armbruster]

Stefan Hajnoczi <address@hidden> writes:

> 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

# hdparm -N /dev/cdrom

/dev/cdrom:
 READ_NATIVE_MAX_ADDRESS failed: Input/output error
# hdparm -N 1024 /dev/cdrom

/dev/cdrom:
 setting max visible sectors to 1024 (temporary)
 READ_NATIVE_MAX_ADDRESS failed: Input/output error
 READ_NATIVE_MAX_ADDRESS failed: Input/output error

Same with and without media.

If the command makes no sense for CD-ROMs, and generally isn't
implemented by them, we should consider not implementing either, by
clearing its IDE_CD bit in ide_cmd_table.