From owner-freebsd-hackers  Sat May  6 12:59:53 2000
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To: Alexander Langer <alex@big.endian.de>
Cc: hackers@FreeBSD.ORG
Subject: Re: problem with ioctl handler in a module 
In-Reply-To: Message from Alexander Langer <alex@big.endian.de> 
   of "Sat, 06 May 2000 20:09:40 +0200." <20000506200940.A8087@cichlids.cichlids.com> 
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Date: Sat, 06 May 2000 12:58:10 -0700
From: Jake Burkholder <jburkhol@home.com>
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> Hello!
> 
> I have:
> 
> int ziva_ioctl(dev_t dev, u_long cmd, caddr_t arg, int flag, struct
> proc* pr)
> 
> when this function catches a ioctl from userspace, called as:
> 	int foo = 199;
> 	ioctl(fd, 10, &foo);
> 
> the u_long cmd contains 10, which is correct (so the ioctl-handler is
> called correctly).
> 
> However, I can't get the value of the int.
> 
> I tried something like:
> 	if (*((int *) arg) == 199)
> 		<bleh>.
> 
> But this doesn't work, <bleh> is not executed. Somehow, I can't access 
> the memory this way.
> 
> Anyone knows, what I'm doing wrong?

The request parameter to ioctl needs to contain length information.

I think you want something like:

#define ZIVA_IOCTL   _IOW('c', 10, int)

int foo = 199;
ioctl(fd, ZIVA_IOCTL, &foo);

Then arg should be right.  See iocomm.h.



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