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Date: Thu, 12 Jul 2001 15:22:09 -0500
From: Yonny Cardenas <ycardena@yahoo.com>
Organization: Ingenieria Integral Ltda
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To: questions@freebsd.org
Subject: Some questions about kernel programming
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Dear Friends

I have some questions about kernel programming:

1. Why I can call some system calls functions into the kernel but
  another not?, for example: I can call printf(), but I can't call
  socket().

2. Into kernel I can call the socket "low level" functions
  that this system calls invoke  sosocket(), soconnect(), etc.
  but, How I do replace the send() system call? Perhaps, Can I call
  write() into kernel with same parameters?
  For example :
  /* res =  send(skt, buf, buflen, 0); */
  res =  write (skt, buf, buflen);

3. How I can copy a pointer string ( character array ) from user space
to
  kernel space using copyin() without the following problem (I can't
  pass the length the explicitly from user land):

struct    MySystemCall_args {
   char *    address;
};

int MySystemCall( p,uap)
  struct proc *p;
  register struct  MySystemCall_args *uap;
{
  char *the_address;

  printf(" ---> uap->address : %s\n", uap->address );
  printf(" ---> (strlen (uap->address) * sizeof(char)) : %d \n",
   (strlen (uap->address) * sizeof(char)) );
  copyin(uap->address, the_address, (strlen (uap->address) *
sizeof(char))
);
  printf("the_address: %s \n", the_address );
  printf("strlen (the_address): %d \n", strlen (the_address) );

When this code run in mode kernel:
  ---> uap->address : 127.0.0.1
  ---> (strlen (uap->address) * sizeof(char)) : 9
  the_address : 127.0.0.1\M-"\M-Y\M-GX\M-p+\M-@@\M-_\M-*\M-@
  strlen (the_address): 20

This crash the kernel later...

Thanks for your help.

-- 
+------------------------------------------------------------------+
| YONNY CARDENAS B.             Apartado Aereo  22828	      	   |
| Systems Engineer    		Santafe de Bogota D.C.   	   |
|				Colombia - South America	   |	
| Student M.Sc.		     	Tels:   +571 6095477  		   | 
| UNIVERSIDAD DE LOS ANDES     	mailto:	y-carden@uniandes.edu.co   | 
|                                	ycardena@yahoo.com         |
+------------------------------------------------------------------+
UNIX is BSD, and FreeBSD is an advanced 4.4BSD


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