minix文件系统源码分析之symlink.c（基于linux1.2.13）

/*
 *  linux/fs/minix/symlink.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  minix symlink handling code
 */

#ifdef MODULE
#include <linux/module.h>
#endif

#include <asm/segment.h>

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/minix_fs.h>
#include <linux/stat.h>

static int minix_readlink(struct inode *, char *, int);
static int minix_follow_link(struct inode *, struct inode *, int, int, struct inode **);

/*
 * symlinks can't do much...
 */
// 操作软链接文件的函数集，在新建软链接文件的时候赋值给inode结构体
struct inode_operations minix_symlink_inode_operations = {
  NULL,      /* no file-operations */
  NULL,      /* create */
  NULL,      /* lookup */
  NULL,      /* link */
  NULL,      /* unlink */
  NULL,      /* symlink */
  NULL,      /* mkdir */
  NULL,      /* rmdir */
  NULL,      /* mknod */
  NULL,      /* rename */
  minix_readlink,    /* readlink */
  minix_follow_link,  /* follow_link */
  NULL,      /* bmap */
  NULL,      /* truncate */
  NULL      /* permission */
};
// 打开软链对应的文件
static int minix_follow_link(struct inode * dir, struct inode * inode,
  int flag, int mode, struct inode ** res_inode)
{
  int error;
  struct buffer_head * bh;

  *res_inode = NULL;
  if (!dir) {
    dir = current->fs->root;
    dir->i_count++;
  }
  if (!inode) {
    iput(dir);
    return -ENOENT;
  }
  if (!S_ISLNK(inode->i_mode)) {
    iput(dir);
    *res_inode = inode;
    return 0;
  }
  if (current->link_count > 5) {
    iput(inode);
    iput(dir);
    return -ELOOP;
  }
  // 读取文件第一块内容
  if (!(bh = minix_bread(inode, 0, 0))) {
    iput(inode);
    iput(dir);
    return -EIO;
  }
  iput(inode);
  current->link_count++;
  // 打开b_data里的保存的文件名对应的文件
  error = open_namei(bh->b_data,flag,mode,res_inode,dir);
  current->link_count--;
  brelse(bh);
  return error;
}
// 读取软链文件的内容，即文件路径
static int minix_readlink(struct inode * inode, char * buffer, int buflen)
{
  struct buffer_head * bh;
  int i;
  char c;

  if (!S_ISLNK(inode->i_mode)) {
    iput(inode);
    return -EINVAL;
  }
  if (buflen > 1023)
    buflen = 1023;
  bh = minix_bread(inode, 0, 0);
  iput(inode);
  if (!bh)
    return 0;
  i = 0;
  while (i<buflen && (c = bh->b_data[i])) {
    i++;
    put_fs_byte(c,buffer++);
  }
  brelse(bh);
  return i;
}