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SubjectRe: linux-2.4.0 breaks grub install into partition
  Perhaps I should comment on this...

From: Alexander Viro <>
Subject: Re: linux-2.4.0 breaks grub install into partition
Date: Sat, 8 Jul 2000 20:48:02 -0400 (EDT)

> No, since you are using the functionality that was never promised to be
> there. Example: fs has a perfect right to copy superblock out of the
> buffer cache and slam it back whenever it wants, completely ignoring any
> changes you've done to buffer cache. Or to keep it in pagecache and don't
> have buffer heads hashed. You are _not_ supposed to bypass r/w
> filesystem

I don't think what GRUB does is a wrong thing basically. Some types
of software always need (or want) to access raw devices, for example,
FDISK programs, filesystem resizers, and fast database servers. So,
AFAIK, all the realistic operating systems export raw devices to
user-level programs and support one or more system calls to keep
anything in the kernel consistent.

For now, the grub shell calls sync() (twice before any operation)
and ioctl(fd, BLKFLSBUF, 0) (after and before operations) under
Linux. I thought that was enough, since sync should make filesystems
and buffer caches consistent, and BLKFLSBUF should flush buffer caches
to actual disks. I even thought that was overkill.

Therefore, I was surprised when I heard that wasn't still enough. If
that is not a problem which should be fixed in Linux, how should we
fix the grub shell? What is supposed to do with raw devices?


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