Date: Sun, 26 Sep 1999 18:26:07 -0700 From: Mike Smith <mike@smith.net.au> To: "Juan Lorenzana" <lorenzaj@agcs.com> Cc: hackers@FreeBSD.org Subject: Re: [Fwd: Bsd Problem] Message-ID: <199909270126.SAA15450@dingo.cdrom.com> In-Reply-To: Your message of "Thu, 23 Sep 1999 21:36:29 PDT." <37EAFFCD.6F9F4B0D@agcs.com>
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>
> I was wondering if I could get help. Doug Madderom is a developer at
> AGCS and has asked me to forward this to the FreeBSD newsgroup. Any
> help is appreciated. Thanks.
Commentary follows:
> I wrote a character device driver using ioct as the method to pass data in a
> structure to and from the device driver. If I do not include either a printf or
> scanf in the application program that uses the driver the pointer the OS passes
> to the ioctl in the driver is not set up right and the driver panics. What am I
> doing wrong ?
I don't think the use or non-use of printf/scanf have anything to do
with the problem here. You've probably made several changes at the
same time and missed the significant one.
> Program that fails ( works if first line in program is a printf)
The program is OK.
> Device driver:
> ----------------------------------------------
> /* alarmio driver for free BDS */
It's "FreeBSD". 8)
> struct Ioctl_args *tmp;
...
> *tmp=*(struct Ioctl_args *)arg;
You never point (tmp) at anything, and the code above (which is wrong)
attempts a structure copy of the structure that (arg) points to into
random space. This line should read
tmp = (struct Ioctl_args *)arg;
Normal programming convention would have you make the assignment in the
declaration of tmp:
static int
alarmioioctl(dev_t dev, int cmd, caddr_t arg, int flag, struct proc *p)
{
struct Ioctl_args *tmp = (struct Ioctl_args *)arg;
Hope this helps.
--
\\ The mind's the standard \\ Mike Smith
\\ of the man. \\ msmith@freebsd.org
\\ -- Joseph Merrick \\ msmith@cdrom.com
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