de2-115-fpga-pong/software/hello_world_bsp/HAL/src/alt_fd_lock.c

/******************************************************************************
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* License Agreement                                                           *
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* Copyright (c) 2004 Altera Corporation, San Jose, California, USA.           *
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#include <errno.h>

#include "priv/alt_file.h"

/*
 * alt_fd_lock() is called as a consequence of an ioctl call to gain exclusive
 * access to a device, i.e.:
 *
 * ioctl (fd, TIOCEXCL, NULL);
 *
 * If there are no other open file descriptors which reference the same
 * device, then alt_fd_lock() will grant the lock. Further calls to open() 
 * for this device will fail until the lock is released.
 *
 * This is done by calling close() for this file descriptor, or by calling:
 *
 * ioctl (fd, TIOCNXCL, NULL);
 *
 * The return value is zero for success, or negative in the case of failure.
 */

int alt_fd_lock (alt_fd* fd)
{
  int i;
  int rc = 0;

  ALT_SEM_PEND(alt_fd_list_lock, 0);

  for (i = 0; i < alt_max_fd; i++)
  {
    if ((&alt_fd_list[i] != fd) && (alt_fd_list[i].dev == fd->dev))
    {
      rc = -EACCES;
      goto alt_fd_lock_exit;
    }
  }
  fd->fd_flags |= ALT_FD_EXCL;

 alt_fd_lock_exit:

  ALT_SEM_POST(alt_fd_list_lock);
  return rc;
}