Messages in this thread |  | | Date | Sat, 11 Nov 2000 12:58:08 -0500 | Subject | Re: [ANNOUNCE] Generalised Kernel Hooks Interface (GKHI) | From | tytso@mit ... |
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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....
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