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SubjectRe: linux-2.4.0 breaks grub install into partition
Andries Brouwer wrote:
> If a program needs the partition starting point, it can use the
> HDIO_GETGEO ioctl which returns a
> struct hd_geometry {
> unsigned char heads;
> unsigned char sectors;
> unsigned short cylinders;
> unsigned long start;
> };

Ah yes, this is what I was looking for. This should be sufficient for
the time (at least until 2^32 sectors become an issue (2 TB disks).

> If one needs the partition starting point from the command line,
> there are various utilities (e.g., hdparm -g) that will print it.
> > Nor does it seem that these exists an ioctl() to find the base
> > device and offset for a partition subdevice, which I have to admit to
> > being rather shocked to find out.
> No. And that is an operation very often used, mostly inside
> the kernel, and also the kernel has no mechanism.
> One sees MKDEV(MAJOR(dev), MINOR(dev)&mask) or similar stuff
> everywhere. In my big "large device number" rewrite, the minorstruct
> of a subdevice has a pointer to the minorstruct of the whole device.
> (Basically because MKDEV() becomes an expensive operation involving
> a search and possibly a memory allocation.)

This would be a very good thing to have.


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