Re: udev and raw support

[Greg KH <greg@kroah.com>]

On Mon, Apr 25, 2005 at 10:39:43PM -0700, Phil Dibowitz wrote:
> Greg KH wrote:
> >
> > What distro are you using?  In order to have udev and raw working
> > together, you need a new version of the raw userspace program (sorry,
> > forgot about this until right now.)  I know SuSE ships it in their
> > distro, don't know about everyone else.
> 
> Debian unstable.
> 
> /sbin/raw seems to be part of util-linux which is at version 2.12p-4 in
> debian unstable - i.e. 2.12p with 4 local debian revisions which may or
> may not include code from later util-linux releases.

I really don't know if they got that patch or not, sorry.

> > Also, why use raw at all?  It's depreciated, nasty code, which no one
> > likes at all, and has no real-world use.  It is also going to be ripped
> > out of the kernel entirely one of these days.  The only people who like
> > it are people who want to create useless benchmarks...
> 
> I've never used it in linux, only in Solaris... but I'm told that it
> will provide better DVD Video read performance. Many of the DVD players
> out there provide support for raw devices, and in fact recommend using them.

For Linux?  Just use O_DIRECT and it should work the same.

> Since even on my high-end system I don't get the DVD playback that I get
> on my living room DVD player, I decided to give it a shot.

My crappy, slow, no-memory, 2+ year old laptop gives great dvd playback,
perhaps you have some other issues with your system (sorry, I'm not
going to be able to help out here, as I don't know anything about video
playback other than it "works for me")

> Why is it depricated? What's wrong with using raw devices?

Because you should use O_DIRECT to access block devices directly, which
properly uses the kernel io subsystems.  raw goes around all of that,
and thinks it is smarter than the kernel.  In the end, it is wrong, and
can be slower.

Anyway, you can get around this by creating the device node by hand if
you really want.  I suggest you file a debian bug to get them to fix the
raw program to work properly with udev.

Good luck,

greg k-h


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