upsdl.c

/*-
 * Copyright (c) 2006, Stephan Uphoff <[email protected]>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>


int prepareFile(const char* filename,int* fdp);
int mapBuffer(char** bufferp,int fd1,int fd2);
int startIO(int fd,char *buffer);

static int pagesize;

#define FILESIZE (32*1024)
static char wbuffer[FILESIZE];

/* Create a FILESIZE sized file - then remove file data from the cache*/
int prepareFile(const char* filename,int* fdp)
{
  int fd;
  int len;
  int status;
  void *addr;

  fd = open(filename,O_CREAT | O_TRUNC | O_RDWR,S_IRWXU);
  if (fd == -1)
    {
      perror("Creating file");
      return fd;
    }
  
  len = write(fd,wbuffer,FILESIZE);
  if (len < 0)
    {
      perror("Write failed");
      return 1;
    }

  status = fsync(fd);
   if (status != 0)
    {
        perror("fsync failed");
	return 1;
    }

  addr = mmap(NULL,FILESIZE, PROT_READ | PROT_WRITE , MAP_SHARED, fd, 0);
  if (addr == MAP_FAILED)
    {
      perror("Mmap failed");
      return 1;
    }

  status = msync(addr,FILESIZE,MS_INVALIDATE | MS_SYNC);
  if (status != 0)
    {
        perror("Msync failed");
	return 1;
    }

  munmap(addr,FILESIZE);

  *fdp = fd;
  return 0;
}


/* mmap a 2 page buffer - first page is from fd1, second page from fd2 */
int mapBuffer(char** bufferp,int fd1,int fd2)
{
  void* addr;
  char *buffer;

  addr = mmap(NULL,pagesize*2, PROT_READ | PROT_WRITE , MAP_SHARED, fd1, 0);
  if (addr == MAP_FAILED)
    {
      perror("Mmap failed");
      return 1;
    }
 
  buffer = addr;
  addr = mmap(buffer + pagesize,pagesize, PROT_READ | PROT_WRITE , MAP_FIXED | 
MAP_SHARED, fd2, 0);
 
  if (addr == MAP_FAILED)
    {
      perror("Mmap2 failed");
      return 1;
    }
  *bufferp = buffer;
  return 0;
}


int startIO(int fd,char *buffer)
{
  ssize_t len;
  len = write(fd,buffer,2*pagesize);
  if (len == -1) 
    {
      perror("write failed");
      return 1;
    }
  return 0;
}


int main(int argc __unused, char *argv[] __unused)
{

  int fdA,fdB,fdDelayA,fdDelayB;
  int status;
  char *bufferA,*bufferB;
  pid_t pid;

  pagesize = getpagesize();

  if ((prepareFile("A",&fdA))
      || (prepareFile("B",&fdB))
      || (prepareFile("DelayA",&fdDelayA))
      || (prepareFile("DelayB",&fdDelayB))
      || (mapBuffer(&bufferA,fdDelayA,fdB))
      || (mapBuffer(&bufferB,fdDelayB,fdA)))
    exit(1);
  
  pid = fork();

  if (pid == 0)
    {
      status = startIO(fdA,bufferA);
      exit(status);
    }

  if (pid == -1)
    {
      exit(1);
    }
  status = startIO(fdB,bufferB);
  exit(status);

}