svn commit: r192535 - head/sys/kern

John Baldwin jhb at
Fri May 22 15:26:08 UTC 2009

On Friday 22 May 2009 9:44:18 am Scott Long wrote:
> John Baldwin wrote:
> > On Thursday 21 May 2009 6:11:02 pm Attilio Rao wrote:
> >> At this point I wonder what's the purpose of maintaining the sleeping
> >> version for such functions?
> > 
> > Actually, I still very much do not like using M_NOWAIT needlessly.  I would 
> > much rather the solution for make_dev() be that the 1 or 2 places that need 
> > to do it with a mutex held instead queue a task to do the actual make_dev() 
> > in a taskqueue when no locks are held.  This is basically what 
> > destroy_dev_sched() is doing.  Perhaps a make_dev_sched() with a similar 
> > callback to be called on completion would be better.  Having a device driver 
> > do all the work to setup the hardware only to fail to create a node in /dev 
> > so that userland can actually use it is pretty rediculous and useless.
> > 
> It's a lot easier for me to handle a failure of make_dev in CAM than it 
> is to decouple the call to it.  Please don't dictate policy.

But what is there for CAM to handle?  I would expect CAM to handle hardware
events such as the devices arriving or leaving.  A temporary memory shortage
it not a hardware event.  As a user, if I insert a USB stick when the system
happens to be temporarily low on memory, is it more useful for the cdev to
appear a few microseconds later from a deferred context once memory is
available or for no device to ever appear at all?

John Baldwin

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