Date: Fri, 10 Nov 2000 19:29:26 -0800
From: "Matt D. Robinson" <[EMAIL PROTECTED]>
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....
- Ted
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