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SubjectRe: rfc: test whether a device has a partition table
On Sat, May 22, 2004 at 01:18:34PM +0200, Uwe Bonnes wrote:

> around last september there was a discussion about the linux kernel
> recognizing "supperfloppys" as disks with bogus partition tables.

Yes - already had forgotten about that - thanks for reviving

> Linux Torvalds wrote at one point in the discussion:

> >I don't mind the 0x00/0x80 "boot flag" checks - those look fairly
> > obvious and look reasonably safe to add to the partitioning code.
>
> The discussion seemed to fade out with no visible result, and for example my
> USB stick "ID 0d7d:1420 Apacer" with a floppy as second partition gets
> recognized as:
> SCSI device sdc: 2880 512-byte hdwr sectors (1 MB)
> sdc: Write Protect is off
> sdc: sdc1 sdc2 sdc3 sdc4

What do you mean by "floppy as second partition"?

> Find appended a patch that does the 0x00/0x80 "boot flag" checks. Please
> discuss and consider for inclusion into the kernel.

> +#define BOOT_IND(p) (get_unaligned(&p->boot_ind))
> #define SYS_IND(p) (get_unaligned(&p->sys_ind))

Hmm. get_unaligned() for a single byte?
I see no reason for these two macros.
Also, it is a good habit to parenthesize macro parameters.

> + /*
> + Some consistancy check for a valid partition table

consistency

> + Boot indicator must either be 0x80 or 0x0 on all primary partitions
> + Only one partition may be marked bootable (0x80)
> + */
> + p = (struct partition *) (data + 0x1be);
> + for (slot = 1 ; slot <= 4 ; slot++, p++) {
> + if ((BOOT_IND(p) != 0x80) && (BOOT_IND(p) != 0x0))
> + return 0;
> + if (BOOT_IND(p) == 0x80)
> + nr_bootable++;
> + }
> + if (nr_bootable > 1)
> + return 0;

I have no objections.

Does it in your case suffice to check for 0 / 0x80 only
(without testing nr_bootable)?

I would prefer to omit that test, until there is at least one
person who shows a boot sector where it is needed.

Andries
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