Re: kern/41189: kernel panic xen dom0 using mke2fs & WAPBL

[Andrew Doran <ad%netbsd.org@localhost>]

The following reply was made to PR kern/41189; it has been noted by GNATS.

From: Andrew Doran <ad%netbsd.org@localhost>
To: David Holland <dholland-bugs%netbsd.org@localhost>
Cc: tech-kern%netbsd.org@localhost, gnats-bugs%NetBSD.org@localhost
Subject: Re: kern/41189: kernel panic xen dom0 using mke2fs & WAPBL
Date: Sat, 9 May 2009 07:30:37 +0000

 On Wed, May 06, 2009 at 11:22:03PM +0000, David Holland wrote:
 
 >  > I disagree. I think the solution is:
 >  > 
 >  > - devfs
 >  > - kill block devices in userspace
 >  > - allow unaligned I/O to disk devices via the raw node
 > 
 > How/why? As I've already explained once (mostly quoted above), devfs
 > will not solve the real problem, just move it around. What are you
 > envisioning that devfs will provide that will avoid the confusion?
 > 
 > And while unaligned I/O seems like a fine idea (as long as it doesn't
 > make physio slower) I don't see how it's relevant.
 > 
 > Please *explain* your reasoning.
 
 I should have been clearer. Have a look at the bigger picture.
 
 - We have longstanding problems with device nodes showing up in multiple
   file systems. For 6.0 we have devfs coming along, which will at some point
   in its development likely eliminate the need to support device nodes on
   other file systems. So devfs will give us a 1:1 mapping between device
   instances and vnodes (or maybe devfs inodes).
 
 - We have longstanding problems providing block device semantics. Block
   devices are an interesting toy but they have no real application. Disk
   character devices suffice with one exception: on NetBSD, transfers on
   these devices must be aligned. So there is no need for physio to cache,
   it could simply buffer to allow misaligned transfers.