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From: Daniel Phillips <news-innominate.list.linux.kernel@innominate.de>
Reply-To: Daniel Phillips <phillips@innominate.de>
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Subject: Re: [ANNOUNCE] Generalised Kernel Hooks Interface (GKHI)
Date: Mon, 13 Nov 2000 11:30:52 +0100
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tytso@mit.edu wrote:
> 
>    Date: Fri, 10 Nov 2000 19:29:26 -0800
>    From: "Matt D. Robinson" <yakker@alacritech.com>
> 
>    We're planning to isolate the write functions as much as possible.
>    In the past, we've been bitten by this whole concept of Linux "raw I/O".
>    When I was at SGI, we were able to write to a block device directly
>    through low-level driver functions that weren't inhibited by any
>    locking, and that was after shutting down all processors and any
>    other outstanding interrupts.  For Linux, I had given up and stuck
>    with the raw I/O interpretation of kiobufs, which is just flat out
>    wrong to do for dumping purposes.  Secondly, as Linus said to me a
>    few weeks ago, he doesn't trust the current disk drivers to be able
>    to reliably dump when a crash occurs.  Don't even ask me to go into
>    all the reasons kiobufs are wrong for crash dumping.  Just read
>    the code -- it'll be obvious enough.
> 
> Oh, yeah, I could have told you that from the beginning.  kiobufs were
> never intended to be crash-dump friendly.  :-)   My preference would be
> that each block device that was going to be doing crash dumping would
> use a special busy-looping driver that's guaranteed never to fail.
> (Sort of like how the serial console driver is done; it's separate from
> the rest of the driver, and does not depend on interrupts working.)
> Hence my comment about putting that separate bit of code in a page which
> is write-protected and segregated from everything else....

This is also needed for single-machine source level kernel debugging.

--
Daniel
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