Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uwvax!barney.cs.wisc.edu!zwilling
From: zwilling@barney.cs.wisc.edu (Mike Zwilling)
Newsgroups: comp.os.mach
Subject: Problem using external pagers
Message-ID: <9510@spool.cs.wisc.edu>
Date: 8 Jan 90 22:35:15 GMT
Sender: news@spool.cs.wisc.edu
Organization: U of Wisconsin CS Dept
Lines: 85

I'm running Mach 2.5 on a micro-vax III and am having problems writing
an external pager.  A couple months ago I posted a request for advice
on writing external pagers, but received none.  Since then I've been
sidetracked, but now I'm working on it again.  

While trying to get my pager to work, I attempted to use the
Network memory server (netmemoryserver) supplied with the 2.5 
distribution.   I seem to be having the same problem with it as with
my pager, so below is a sample program utilizing the netmemoryserver
which demonstrates the problem.  Basically, I can allocate the
memory, but when I first "touch" it, a bus error occurs.  If I replace
the vm_map call with a vm_allocate, everything works fine, so apparently
when the page fault occurs, the netmemoryserver is not being 
"activated."  

Any advice would be greatly appreciated, even confirmation that the
attached program is correct.  If I get it running, I'll post the
solution.

Thanks in advance,

Mike Zwilling   University of Wisconsin -- Madison              
Computer Sciences Dept.
1210 W. Dayton St.
Madison, WI  53706    email: zwilling@cs.wisc.edu   ph# (608) 263-4076

/********************** cut here **********************************/

#include <mach.h>
#include <servers/netname.h>
#include <mach_error.h>
#include <netmemory.h>
#include <stdio.h>
#include <strings.h>


main()
{
    port_t          mem_port;
    memory_object_t paging_object;
    port_t          control_port;
    int             serv_err;
    kern_return_t   retcode;
    vm_address_t    address;
    char            c;

    printf("Looking up port for memory server\n");
    retcode = netname_look_up(name_server_port,"",
			      "netmemoryserver", &mem_port);
    if (retcode != KERN_SUCCESS) {       
	mach_error("error looking up port for memory server",retcode);
	printf("memory server may not be running\n");
	exit(1);
    }

    printf("Allocating memory object\n");
    retcode = netmemory_create(mem_port, 8192, &paging_object, 
			       &control_port);
    if (retcode != KERN_SUCCESS)
	mach_error("Error from netmemory_create is",retcode);

    /*
     * I've tried both including and excluding this call
     * init_netmemory(control_port);
     */

    printf("Allocating region in the  memory object\n");
    retcode = vm_map(task_self_, &address, 4096, 0, TRUE, 
		     paging_object, 0, 0, VM_PROT_WRITE, 
		     VM_PROT_WRITE, VM_INHERIT_SHARE);
    if (retcode != KERN_SUCCESS)
    mach_error("Error from vm_map is",retcode);
      

    c = * ((char*)address);          /* crashes on this line */
    *(char*)address = 'X';           /* or this line */
    *(((char*)address) + 1) = '\0';  /* or this line */
    printf("Data on page 1 is: %s\n", (char*)address);
}

--
Mike Zwilling   University of Wisconsin -- Madison              
Computer Sciences Dept.
1210 W. Dayton St.
Madison, WI  53706    email: zwilling@cs.wisc.edu   ph# (608) 263-4076