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SubjectRe: [ANNOUNCE] Generalised Kernel Hooks Interface (GKHI)
Date
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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