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From: y-carden@uniandes.edu.co
To: questions@freebsd.org
Subject: Some questions about kernel programming
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Date: Thu, 12 Jul 2001 06:58:09 -0500
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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		   |
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| UNIVERSIDAD DE LOS ANDES	mailto: y-carden@uniandes.edu.co   | 
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