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SubjectRe: linux-2.4.0 breaks grub install into partition
On Sat, Jul 08, 2000 at 02:50:10PM +0200, Torsten Duwe wrote:

> here's a problem we've stumbled across testing the 2.4.0 pre-kernels:
> installing grub (0.5.94 if that should matter) into the boot block of a
> partition mounted r/w no longer works; it flawlessly used to in 2.2.x .
>
> A little investigation using strace and friends shows that grub does its
> proper job, finds the right spots and writes there. The write to the
> partition boot block though is somehow discarded, but no error is returned.
>
> Linux kernel people be informed that grub uses the whole-disk device
> (e.g. /dev/hda) to do its job,

Yes, there are some coherency problems various places.

The sequence mkswap; swapon fails for certain kernels,
unless mkswap does fsync(DEV).

Linux does not guarantee coherency between hda and hda1.
For example, cfdisk will show filesystem labels.
If one showed a label (accessed by cfdisk via /dev/hda)
and then changed it (via /dev/hda1) and then used cfdisk
again, the old contents would be shown. Here a BLKFLSBUF helped.

Sometimes the result of fdisk disappears - one uses fdisk,
rechecks with a new fdisk call that all is really well, reboots,
and finds the old partition table. I am not sure what precisely happens.
Perhaps a dirty (super)block written back, destroying fdisk's changes.

Anyway, whole disk access is a bit suspect in Linux.
The BLKFLSBUF and sync() kludges help a little but still
do not guarantee correct operation.

Andries

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