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

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

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.