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Date: Wed, 18 Jun 97 19:32:00 EDT
From: luoqi@watermarkgroup.com (Luoqi Chen)
Message-Id: <9706182332.AA25334@watermarkgroup.com>
To: yifeng@ecsl.cs.sunysb.edu
Subject: Re:  no subject (file transmission)
Cc: hackers@FreeBSD.Org
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> 1) How to get the system time and user time, used by a process, in the kernel?
>    I have tried to use getrusage() function in the /sys/kern/kern_resource.c, 
>    but it won't work.  I can not reboot the machine successfully.  I bet I 
>    have done something wrong; neither this is not a good way to do it nor I do
>    not use it currectly.  
Do not call getrusage(), call calcru() instead,
	
	struct timeval utime, stime, itime;
	struct proc *p;

	...
	calcru(p, &utime, &stime, &itime);
	...

> 2) How to open a file and write messages into the file in the kernel?

To open a file,

	char *path;
	struct vnode *vp;
	struct nameidata nd;
	struct proc *p;
	int error;

	NDINIT(&nd, LOOKUP, FOLLOW, UIO_USERSPACE, path, p);
	error = vn_open(&nd, O_CREAT|FWRITE, 0644);
	if (error) {
	}
	vp = nd.ni_vp;
	VOP_UNLOCK(vp);

keep the vp around, that's your handle to the file.

To close it,
	error = vn_close(vp, FWRITE, p->p_ucred, p);

To write to it,
	error = vn_rdwr(UIO_WRITE, vp, buf, len, 0, UIO_SYSSPACE,
		IO_APPEND|IO_UNIT, p->ucred, (int *)0, p);