Re: best way to access device driver functions

[Kyle Moffett <mrmacman_g4@mac.com>]

On Sep 16, 2005, at 12:02:59, linux-os (Dick Johnson) wrote:
> Somebody reported to me that there was some special "optimization"  
> in Linux that interpreted ioctl() function calls without regard to  
> the specific device that was open (gawd I hope not), and that if  
> you used "already-used" function numbers for your device-specific  
> ioctl(), then strange things would occur.

IIRC, that used to be the case, but isn't anymore.

> However, the kernel is now LOCKED during an ioctl() call. Older  
> Linux versions didn't lock the kernel. The upshotof this is that if  
> you have some ioctl() function that takes some time, like testing  
> the memory in your board, you will find the system unresponsive  
> during that test! You can unlock the kernel in your ioctl() if this  
> is a problem.

This is *completely* wrong.  The kernel used to lock_kernel() for  
*every* ioctl.  Recent changes added locked and unlocked ioctls, such  
that ioctls that do not need the BKL can ignore it completely.  You  
claimed to have read the code, given this typical Wrongbot statement,  
I guess I can say for sure that you didn't.

Cheers,
Kyle Moffett

--
Premature optimization is the root of all evil in programming
  -- C.A.R. Hoare

PS:  Use a different email service!  Your "I tried to kill it with  
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I am not the intended recipient for the following email text.  I will  
destroy all copies of this information, including further copies of  
it, because I am not the intended recipient of those either.  Plonk!
> .
> I apologize for the following. I tried to kill it with the above dot :
>
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