Re: udev and raw support

[Greg KH <greg@kroah.com>]

On Mon, Apr 25, 2005 at 11:14:36PM -0700, Phil Dibowitz wrote:
> Greg KH wrote:
> > 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.
> 
> Fair enough. Wouldn't it make sense to make a simple raw module that
> simply was equivalent to opening the block device with O_DIRECT if for
> no other reason than, erm, "backwards" compatiblity with other unices -
> for ease of the writers of mplayer/xine/ogle/etc.?

No, raw creates a char device.  O_DIRECT is a block device.  Two totally
different interfaces.

And hey, just prod those "other unices" to offer O_DIRECT support if you
need that kind of compatibility :)

> > 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.
> 
> I would be interested to experiment, even though I'm sure you're
> right... but I think I'm missing something... don't the major/minor
> number need to be the same:
> 
> [phil@rider rc2.d]$ sudo mknod /dev/raw/raw1 c 22 0

I think raw1 should be 22 1, not 22 0.  Isn't 22 0 rawctl?  Oops, no
rawctl is 162 0, so shouldn't raw1 be 162 1?

Major 22 char device is reserved for a Digi serial card, which I don't
think you are trying to use :)

Yup, making the device node by hand here, on a gentoo box which does not
have an updated raw command worked just fine.

See Documentation/devices.txt for more info on what you should be using
for major/minor numbers here.

thanks,

greg k-h


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_ide95&alloc_id\x14396&op=click
_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel