From owner-freebsd-hackers  Thu Aug 17 22:27: 1 2000
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To: freebsd-hackers@freebsd.org
Subject: 'group' in ioctl()
From: FUJITA Kazutoshi <fujita@soum.co.jp>
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Date: Fri, 18 Aug 2000 14:26:50 +0900
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Hi, hackers.

I have been given the task of writing a PCI device driver for
a special card on 4.0-RELEASE.
But I'm novice in device driver programming.

In writing ioctl routine, I have to decide ioctl command code.
So I saw some other device driver source code and system header
files, I found some macros in <sys/ioccom.h>.

#define _IOC(inout,group,num,len) \
	((unsigned long)(inout | ((len & IOCPARM_MASK) << 16) | ((group) << 8) | (num)))
#define _IO(g,n)        _IOC(IOC_VOID,  (g), (n), 0)
#define _IOR(g,n,t)     _IOC(IOC_OUT,   (g), (n), sizeof(t))
#define _IOW(g,n,t)     _IOC(IOC_IN,    (g), (n), sizeof(t))
/* this should be _IORW, but stdio got there first */
#define _IOWR(g,n,t)    _IOC(IOC_INOUT, (g), (n), sizeof(t))

What 'group' should I use ?


Regards,


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