open.c

上一个上传的有问题,这个是好的。visopsys包括系统内核和GUI的全部SOURCE code ,还包括一些基本的docs文档。里面src子目录对应所有SOURCE code.对于想研究操作系统的朋

// 
//  Visopsys
//  Copyright (C) 1998-2007 J. Andrew McLaughlin
//  
//  This library is free software; you can redistribute it and/or modify it
//  under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation; either version 2.1 of the License, or (at
//  your option) any later version.
//
//  This library is distributed in the hope that it will be useful, but
//  WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
//  General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public License
//  along with this library; if not, write to the Free Software Foundation,
//  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
//  open.c
//

// This is the standard "open" function, as found in standard C libraries

#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/api.h>


int open(const char *fileName, int flags)
{
  // Excerpted from the GNU man page:
  //
  // The open() system call is used to convert a pathname into a file
  // descriptor (a small, non-negative integer for use in subsequent I/O as
  // with read, write, etc.).  The file offset is set to the beginning of
  // the file.
  //
  // The parameter flags is one of O_RDONLY, O_WRONLY or O_RDWR which
  // request opening the file read-only, write-only or read/write, respec-
  // tively, bitwise-or'ed with zero or more of the following:
  //
  // O_CREAT
  //   If the file does not exist it will be created.
  // O_TRUNC
  //   If the file already exists and is a regular file and the open
  //   mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be
  //   truncated to length 0.
  // O_EXCL When used with O_CREAT, if the file already exists it is an
  //   error and the open will fail.
  // O_APPEND
  //   The file is opened in append mode.  Before each write, the file
  //   pointer is positioned at the end of the file, as if with lseek.
  // O_DIRECTORY
  //   If pathname is not a directory, cause the open to fail.

  int status = 0;
  fileStream *theStream = NULL;
  int newFlags = 0;

  // We have to adapt the UNIX/POSIX flags to our flags

  if (visopsys_in_kernel)
    return (errno = ERR_BUG);

  // First the 'exclusive' ones
  if (flags & O_RDONLY)
    newFlags |= OPENMODE_READ;
  else if (flags & O_WRONLY)
    newFlags |= OPENMODE_WRITE;
  else if (flags & O_RDWR)
    newFlags |= OPENMODE_READWRITE;

  // The rest
  if (flags & O_CREAT)
    newFlags |= OPENMODE_CREATE;
  if (flags & O_TRUNC)
    newFlags |= OPENMODE_TRUNCATE;
  if ((newFlags & OPENMODE_CREATE) && (flags & O_EXCL))
    newFlags |= ~OPENMODE_CREATE;
  if ((newFlags & OPENMODE_TRUNCATE) && (flags & O_APPEND))
    newFlags |= ~OPENMODE_TRUNCATE;

  // Get memory for the file stream
  theStream = malloc(sizeof(fileStream));
  if (theStream == NULL)
    return (errno = ERR_MEMORY);

  bzero(theStream, sizeof(fileStream));
  status = fileStreamOpen(fileName, newFlags, theStream);
  if (status < 0)
    {
      free(theStream);
      return (errno = status);
    }

  if ((flags & O_DIRECTORY) && (theStream->f.type != dirT))
    {
      // Supposed to fail if not a directory
      fileStreamClose(theStream);
      free(theStream);
      return (errno = ERR_NOTADIR);
    }

  // If we're not appending, seek to the beginning of the file, since the
  // fileStreamOpen() call is automatically in 'append' mode
  if (!(flags & O_APPEND))
    {
      status = fileStreamSeek(theStream, 0);
      if (status < 0)
	{
	  fileStreamClose(theStream);
	  free(theStream);
	  return (errno = status);
	}
    }

  return ((int) theStream);
}