minix文件系统源码分析之inode.c(基于linux1.2.13)

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

#ifdef MODULE
#include <linux/module.h>
#include <linux/version.h>
#else
#define MOD_INC_USE_COUNT
#define MOD_DEC_USE_COUNT
#endif

#include <linux/sched.h>
#include <linux/minix_fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/locks.h>

#include <asm/system.h>
#include <asm/segment.h>
#include <asm/bitops.h>

void minix_put_inode(struct inode *inode)
{
  if (inode->i_nlink)
    return;
  // 文件大小变成0
  inode->i_size = 0;
  // 删除inode的内容
  minix_truncate(inode);
  // 释放inode节点,插入空闲队列
  minix_free_inode(inode);
}

// 回写超级块内容
static void minix_commit_super (struct super_block * sb,
             struct minix_super_block * ms)
{
  // sb->u.minix_sb.s_sbh是管理该超级块的buffer 
  mark_buffer_dirty(sb->u.minix_sb.s_sbh, 1);
  sb->s_dirt = 0;
}
// 回写超级块信息到硬盘
void minix_write_super (struct super_block * sb)
{
  struct minix_super_block * ms;
  // 没有设置只读标记
  if (!(sb->s_flags & MS_RDONLY)) {
    ms = sb->u.minix_sb.s_ms;

    if (ms->s_state & MINIX_VALID_FS)
      ms->s_state &= ~MINIX_VALID_FS;
    minix_commit_super (sb, ms);
  }
  sb->s_dirt = 0;
}

// 回写超级块的内容 
void minix_put_super(struct super_block *sb)
{
  int i;
  // 加锁
  lock_super(sb);
  // 
  if (!(sb->s_flags & MS_RDONLY)) {
    sb->u.minix_sb.s_ms->s_state = sb->u.minix_sb.s_mount_state;
    mark_buffer_dirty(sb->u.minix_sb.s_sbh, 1);
  }
  // 置为0说明没有不在使用
  sb->s_dev = 0;
  // 回写inode位图信息
  for(i = 0 ; i < MINIX_I_MAP_SLOTS ; i++)
    brelse(sb->u.minix_sb.s_imap[i]);
  // 回写块位图信息
  for(i = 0 ; i < MINIX_Z_MAP_SLOTS ; i++)
    brelse(sb->u.minix_sb.s_zmap[i]);
  // 回写超级块其他字段
  brelse (sb->u.minix_sb.s_sbh);
  // 解锁
  unlock_super(sb);
  MOD_DEC_USE_COUNT;
  return;
}

static struct super_operations minix_sops = { 
  minix_read_inode,
  NULL,
  minix_write_inode,
  minix_put_inode,
  minix_put_super,
  minix_write_super,
  minix_statfs,
  minix_remount
};
// 重新挂载文件系统,其实只能改变flag,而不是卸载再挂载
int minix_remount (struct super_block * sb, int * flags, char * data)
{
  struct minix_super_block * ms;
  // s_ms保存的minix文件系统超级块的信息
  ms = sb->u.minix_sb.s_ms;
  if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY))
    return 0;
  if (*flags & MS_RDONLY) {
    if (ms->s_state & MINIX_VALID_FS ||
        !(sb->u.minix_sb.s_mount_state & MINIX_VALID_FS))
      return 0;
    /* Mounting a rw partition read-only. */
    ms->s_state = sb->u.minix_sb.s_mount_state;
    mark_buffer_dirty(sb->u.minix_sb.s_sbh, 1);
    sb->s_dirt = 1;
    minix_commit_super (sb, ms);
  }
  else {
      /* Mount a partition which is read-only, read-write. */
    sb->u.minix_sb.s_mount_state = ms->s_state;
    ms->s_state &= ~MINIX_VALID_FS;
    mark_buffer_dirty(sb->u.minix_sb.s_sbh, 1);
    sb->s_dirt = 1;

    if (!(sb->u.minix_sb.s_mount_state & MINIX_VALID_FS))
      printk ("MINIX-fs warning: remounting unchecked fs, "
        "running fsck is recommended.\n");
    else if ((sb->u.minix_sb.s_mount_state & MINIX_ERROR_FS))
      printk ("MINIX-fs warning: remounting fs with errors, "
        "running fsck is recommended.\n");
  }
  return 0;
}

// 读超级块
struct super_block *minix_read_super(struct super_block *s,void *data, 
             int silent)
{
  struct buffer_head *bh;
  struct minix_super_block *ms;
  int i,dev=s->s_dev,block;

  if (32 != sizeof (struct minix_inode))
    panic("bad i-node size");
  MOD_INC_USE_COUNT;
  lock_super(s);
  set_blocksize(dev, BLOCK_SIZE);
  // 读入超级块
  if (!(bh = bread(dev,1,BLOCK_SIZE))) {
    // 重置为未使用标记
    s->s_dev=0;
    unlock_super(s);
    printk("MINIX-fs: unable to read superblock\n");
    MOD_DEC_USE_COUNT;
    return NULL;
  }
  // 转成minix类型的超级块类型
  ms = (struct minix_super_block *) bh->b_data;
  // s是vfs的通用结构体,minix_sb是存储超级块信息的结构,s_ms是保存minix类型超级块的结构
  s->u.minix_sb.s_ms = ms;
  // bh是管理该超级块的buffer
  s->u.minix_sb.s_sbh = bh;
  // 
  s->u.minix_sb.s_mount_state = ms->s_state;
  // 块大小
  s->s_blocksize = 1024;
  // 右移10位,用于算出第几块
  s->s_blocksize_bits = 10;
  // inode的个数
  s->u.minix_sb.s_ninodes = ms->s_ninodes;
  // 文件系统的总块数,包括数据块,保存元数据的块
  s->u.minix_sb.s_nzones = ms->s_nzones;
  // inode位图块数
  s->u.minix_sb.s_imap_blocks = ms->s_imap_blocks;
  // 数据块位图块数
  s->u.minix_sb.s_zmap_blocks = ms->s_zmap_blocks;
  // 第一个数据块在硬盘的块号
  s->u.minix_sb.s_firstdatazone = ms->s_firstdatazone;
  // 右移s_log_zone_size位得到每块的大小,区别于用于存储数据的块大小 
  s->u.minix_sb.s_log_zone_size = ms->s_log_zone_size;
  // 单文件最大字节数 
  s->u.minix_sb.s_max_size = ms->s_max_size;
  // 文件系统魔数
  s->s_magic = ms->s_magic;
  // minix系统的版本
  if (s->s_magic == MINIX_SUPER_MAGIC) {
    // 目录项结构体minix_dir_entry的大小,两个字节存inode号,14个存文件名
    s->u.minix_sb.s_dirsize = 16;
    // 文件名长度
    s->u.minix_sb.s_namelen = 14;
  } else if (s->s_magic == MINIX_SUPER_MAGIC2) {
    s->u.minix_sb.s_dirsize = 32;
    s->u.minix_sb.s_namelen = 30;
  } else {
    // 魔数不对
    s->s_dev = 0;
    unlock_super(s);
    brelse(bh);
    if (!silent)
      printk("VFS: Can't find a minix filesystem on dev 0x%04x.\n", dev);
    MOD_DEC_USE_COUNT;
    return NULL;
  }
  // 初始化
  for (i=0;i < MINIX_I_MAP_SLOTS;i++)
    s->u.minix_sb.s_imap[i] = NULL;
  for (i=0;i < MINIX_Z_MAP_SLOTS;i++)
    s->u.minix_sb.s_zmap[i] = NULL;
  block=2;
  // 从第二块开始读,第一块保存超级块信息了,第二块起的n块保存块位图、inode位图
  for (i=0 ; i < s->u.minix_sb.s_imap_blocks ; i++)
    if ((s->u.minix_sb.s_imap[i]=bread(dev,block,BLOCK_SIZE)) != NULL)
      block++;
    else
      break;
  for (i=0 ; i < s->u.minix_sb.s_zmap_blocks ; i++)
    if ((s->u.minix_sb.s_zmap[i]=bread(dev,block,BLOCK_SIZE)) != NULL)
      block++;
    else
      break;
  // 没有全部读成功,报错
  if (block != 2+s->u.minix_sb.s_imap_blocks+s->u.minix_sb.s_zmap_blocks) {
    for(i=0;i<MINIX_I_MAP_SLOTS;i++)
      brelse(s->u.minix_sb.s_imap[i]);
    for(i=0;i<MINIX_Z_MAP_SLOTS;i++)
      brelse(s->u.minix_sb.s_zmap[i]);
    s->s_dev=0;
    unlock_super(s);
    brelse(bh);
    printk("MINIX-fs: bad superblock or unable to read bitmaps\n");
    MOD_DEC_USE_COUNT;
    return NULL;
  }
  // 操作系统查找空闲项的时候,成功则返回第几项,失败则返回0,所以第0项不使用。否则返回0无法判断语义
  set_bit(0,s->u.minix_sb.s_imap[0]->b_data);
  set_bit(0,s->u.minix_sb.s_zmap[0]->b_data);
  unlock_super(s);
  /* set up enough so that it can read an inode */
  s->s_dev = dev;
  // 操作超级块的函数集
  s->s_op = &minix_sops;
  // 获取第MINIX_ROOT_INO即第1个inode(第0个不用),第一个inode是根inode,即文件系统的起点
  s->s_mounted = iget(s,MINIX_ROOT_INO);
  // 获取失败则报错
  if (!s->s_mounted) {
    s->s_dev = 0;
    brelse(bh);
    printk("MINIX-fs: get root inode failed\n");
    MOD_DEC_USE_COUNT;
    return NULL;
  }
  if (!(s->s_flags & MS_RDONLY)) {
    ms->s_state &= ~MINIX_VALID_FS;
    mark_buffer_dirty(bh, 1);
    s->s_dirt = 1;
  }
  if (!(s->u.minix_sb.s_mount_state & MINIX_VALID_FS))
    printk ("MINIX-fs: mounting unchecked file system, "
      "running fsck is recommended.\n");
   else if (s->u.minix_sb.s_mount_state & MINIX_ERROR_FS)
    printk ("MINIX-fs: mounting file system with errors, "
      "running fsck is recommended.\n");
  return s;
}
// 显示minix文件系统的参数,块数、可用数、文件名长度等
void minix_statfs(struct super_block *sb, struct statfs *buf)
{
  long tmp;

  put_fs_long(MINIX_SUPER_MAGIC, &buf->f_type);
  put_fs_long(1024, &buf->f_bsize);
  tmp = sb->u.minix_sb.s_nzones - sb->u.minix_sb.s_firstdatazone;
  tmp <<= sb->u.minix_sb.s_log_zone_size;
  put_fs_long(tmp, &buf->f_blocks);
  tmp = minix_count_free_blocks(sb);
  put_fs_long(tmp, &buf->f_bfree);
  put_fs_long(tmp, &buf->f_bavail);
  put_fs_long(sb->u.minix_sb.s_ninodes, &buf->f_files);
  put_fs_long(minix_count_free_inodes(sb), &buf->f_ffree);
  put_fs_long(sb->u.minix_sb.s_namelen, &buf->f_namelen);
  /* Don't know what value to put in buf->f_fsid */
}
// i_data里保存的是文件内容的块号和硬盘块号的对应关系
#define inode_bmap(inode,nr) ((inode)->u.minix_i.i_data[(nr)])
// bh->b_data保存的是文件内容块号和硬盘块号的对应关系
static int block_bmap(struct buffer_head * bh, int nr)
{
  int tmp;

  if (!bh)
    return 0;
  tmp = ((unsigned short *) bh->b_data)[nr];
  brelse(bh);
  return tmp;
}
// 获取文件内容的逻辑块号在硬盘中对应的实际块号
int minix_bmap(struct inode * inode,int block)
{
  int i;

  if (block<0) {
    printk("minix_bmap: block<0");
    return 0;
  }
  if (block >= 7+512+512*512) {
    printk("minix_bmap: block>big");
    return 0;
  }
  // 小于7的块号直接存在inode里
  if (block < 7)
    return inode_bmap(inode,block);
  block -= 7;
  // inode的i_data的第八个元素保存了一个块号,该块里的内容保存了512个块号,即第8块开始的文件内容
  if (block < 512) {
    // 先拿到一级块号
    i = inode_bmap(inode,7);
    if (!i)
      return 0;
    // 把一级块号对应的数据从硬盘读取进来,然后再根据偏移找到对应的二级块号,即文件内容对应的块号
    return block_bmap(bread(inode->i_dev,i,BLOCK_SIZE),block);
  }
  block -= 512;
  /*
    inode的i_data的第九个元素保存了一个块号,该块包括了512块号,
    512块号每个块号对应的块又保存了512个块号,最后的512块号保存了文件内容的块号
  */
  i = inode_bmap(inode,8);
  if (!i)
    return 0;
  // >>9即除以512算出在哪个二级块
  i = block_bmap(bread(inode->i_dev,i,BLOCK_SIZE),block>>9);
  if (!i)
    return 0;
  // &511算出偏移
  return block_bmap(bread(inode->i_dev,i,BLOCK_SIZE),block & 511);
}
// 读取buffer中某个硬盘数据块对应的内容,create=1,说明没有对应数据块则创建一个
static struct buffer_head * inode_getblk(struct inode * inode, int nr, int create)
{
  int tmp;
  unsigned short *p;
  struct buffer_head * result;

  p = inode->u.minix_i.i_data + nr;
repeat:
  // 硬盘块号
  tmp = *p;
  if (tmp) {
    // 判断是不是在buffer里。
    result = getblk(inode->i_dev, tmp, BLOCK_SIZE);
    // 判断p指向块号是不是变了,是的话说明获取的数据result不是对的
    if (tmp == *p)
      return result;
    brelse(result);
    goto repeat;
  }
  // create是0说明不需要新建,等于1即找不到的时候新建一个
  if (!create)
    return NULL;
  // 从硬盘中创建一个新的块
  tmp = minix_new_block(inode->i_sb);
  if (!tmp)
    return NULL;
  // 
  result = getblk(inode->i_dev, tmp, BLOCK_SIZE);
  // p非空说明该项被使用了,则释放,可能因为中断引起的
  if (*p) {
    minix_free_block(inode->i_sb,tmp);
    brelse(result);
    goto repeat;
  }
  // 保存映射关系
  *p = tmp;
  // 创建时间
  inode->i_ctime = CURRENT_TIME;
  // inode新增了一个映射关系,需要回写到硬盘 
  inode->i_dirt = 1;
  return result;
}

// 读取buffer中硬盘某个块的对应的数据,或者新建一个块,bh->b_data保存了512个文件块号到硬盘块号。逻辑类似上面的函数
static struct buffer_head * block_getblk(struct inode * inode, 
  struct buffer_head * bh, int nr, int create)
{
  int tmp;
  unsigned short *p;
  struct buffer_head * result;

  if (!bh)
    return NULL;
  // 数据不是最新的,则先刷新缓存的数据
  if (!bh->b_uptodate) {
    ll_rw_block(READ, 1, &bh);
    wait_on_buffer(bh);
    if (!bh->b_uptodate) {
      brelse(bh);
      return NULL;
    }
  }
  p = nr + (unsigned short *) bh->b_data;
repeat:
  tmp = *p;
  if (tmp) {
    result = getblk(bh->b_dev, tmp, BLOCK_SIZE);
    if (tmp == *p) {
      brelse(bh);
      return result;
    }
    brelse(result);
    goto repeat;
  }
  if (!create) {
    brelse(bh);
    return NULL;
  }
  tmp = minix_new_block(inode->i_sb);
  if (!tmp) {
    brelse(bh);
    return NULL;
  }
  result = getblk(bh->b_dev, tmp, BLOCK_SIZE);
  if (*p) {
    minix_free_block(inode->i_sb,tmp);
    brelse(result);
    goto repeat;
  }
  *p = tmp;
  mark_buffer_dirty(bh, 1);
  brelse(bh);
  return result;
}
/*
  获取硬盘某块数据的内容,是对上面两个函数的封装,
  主要是计算block的逻辑,inode_getblk,block_getblk是已经知道要获取
  的是硬盘的哪个块。minix_getblk是给这两个函数计算出最终的硬盘块号
*/
struct buffer_head * minix_getblk(struct inode * inode, int block, int create)
{
  struct buffer_head * bh;

  if (block<0) {
    printk("minix_getblk: block<0");
    return NULL;
  }
  if (block >= 7+512+512*512) {
    printk("minix_getblk: block>big");
    return NULL;
  }
  if (block < 7)
    return inode_getblk(inode,block,create);
  block -= 7;
  if (block < 512) {
    bh = inode_getblk(inode,7,create);
    return block_getblk(inode, bh, block, create);
  }
  block -= 512;
  bh = inode_getblk(inode,8,create);
  bh = block_getblk(inode, bh, block>>9, create);
  return block_getblk(inode, bh, block & 511, create);
}
// 读某块内容,先从buffer获取,没有的话再去读取硬盘里的数据
struct buffer_head * minix_bread(struct inode * inode, int block, int create)
{
  struct buffer_head * bh;
  // 从buffer里读取对应硬盘块的数据
  bh = minix_getblk(inode,block,create);
  // 失败或者是最新的则返回
  if (!bh || bh->b_uptodate)
    return bh;
  // 获取到但是不是最新的数据则调驱动层去读取最新的
  ll_rw_block(READ, 1, &bh);
  wait_on_buffer(bh);
  // 是最新的则返回
  if (bh->b_uptodate)
    return bh;
  brelse(bh);
  return NULL;
}

void minix_read_inode(struct inode * inode)
{
  struct buffer_head * bh;
  struct minix_inode * raw_inode;
  int block, ino;
  // inode号
  ino = inode->i_ino;
  inode->i_op = NULL;
  inode->i_mode = 0;
  if (!ino || ino >= inode->i_sb->u.minix_sb.s_ninodes) {
    printk("Bad inode number on dev 0x%04x: %d is out of range\n",
      inode->i_dev, ino);
    return;
  }
  // 文件系统第一块是引导扇区,第二块是超级块,算出inode在硬盘的块号,imap是存储数据块位图相关的信息需要的空大小
  block = 2 + inode->i_sb->u.minix_sb.s_imap_blocks +
        inode->i_sb->u.minix_sb.s_zmap_blocks +
        (ino-1)/MINIX_INODES_PER_BLOCK;
  // 把整一块读进来
  if (!(bh=bread(inode->i_dev,block, BLOCK_SIZE))) {
    printk("Major problem: unable to read inode from dev 0x%04x\n",
      inode->i_dev);
    return;
  }
  // 算出inode在该块的块内偏移,得到inode的内容
  raw_inode = ((struct minix_inode *) bh->b_data) +
        (ino-1)%MINIX_INODES_PER_BLOCK;
  // 赋值过去
  inode->i_mode = raw_inode->i_mode;
  inode->i_uid = raw_inode->i_uid;
  inode->i_gid = raw_inode->i_gid;
  inode->i_nlink = raw_inode->i_nlinks;
  inode->i_size = raw_inode->i_size;
  inode->i_mtime = inode->i_atime = inode->i_ctime = raw_inode->i_time;
  inode->i_blocks = inode->i_blksize = 0;
  // 如果是字符或者块文件,i_zone[0]保存的是设备号
  if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode))
    inode->i_rdev = raw_inode->i_zone[0];
  // 一般文件i_zone保存的是文件内容的块号
  else for (block = 0; block < 9; block++)
    inode->u.minix_i.i_data[block] = raw_inode->i_zone[block];
  // 用完释放
  brelse(bh);
  // 根据文件类型赋值对应的操作函数集
  if (S_ISREG(inode->i_mode))
    inode->i_op = &minix_file_inode_operations;
  else if (S_ISDIR(inode->i_mode))
    inode->i_op = &minix_dir_inode_operations;
  else if (S_ISLNK(inode->i_mode))
    inode->i_op = &minix_symlink_inode_operations;
  else if (S_ISCHR(inode->i_mode))
    inode->i_op = &chrdev_inode_operations;
  else if (S_ISBLK(inode->i_mode))
    inode->i_op = &blkdev_inode_operations;
  else if (S_ISFIFO(inode->i_mode))
    init_fifo(inode);
}

static struct buffer_head * minix_update_inode(struct inode * inode)
{
  struct buffer_head * bh;
  struct minix_inode * raw_inode;
  int ino, block;

  ino = inode->i_ino;
  if (!ino || ino >= inode->i_sb->u.minix_sb.s_ninodes) {
    printk("Bad inode number on dev 0x%04x: %d is out of range\n",
      inode->i_dev, ino);
    inode->i_dirt = 0;
    return 0;
  }
  // 算出inode在硬盘哪个数据块,s_imap_blocks和s_zmap_blocks是数据位图和inode位图的块数
  block = 2 + inode->i_sb->u.minix_sb.s_imap_blocks + inode->i_sb->u.minix_sb.s_zmap_blocks +
    (ino-1)/MINIX_INODES_PER_BLOCK;
  if (!(bh=bread(inode->i_dev, block, BLOCK_SIZE))) {
    printk("unable to read i-node block\n");
    inode->i_dirt = 0;
    return 0;
  }
  // 算出inode在这个数据块的偏移
  raw_inode = ((struct minix_inode *)bh->b_data) +
    (ino-1)%MINIX_INODES_PER_BLOCK;
  raw_inode->i_mode = inode->i_mode;
  raw_inode->i_uid = inode->i_uid;
  raw_inode->i_gid = inode->i_gid;
  raw_inode->i_nlinks = inode->i_nlink;
  raw_inode->i_size = inode->i_size;
  raw_inode->i_time = inode->i_mtime;
  if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode))
    raw_inode->i_zone[0] = inode->i_rdev;
  else for (block = 0; block < 9; block++)
    raw_inode->i_zone[block] = inode->u.minix_i.i_data[block];
  inode->i_dirt=0;
  // 回写inode内容到硬盘,上面的代码见read_inode注释
  mark_buffer_dirty(bh, 1);
  return bh;
}

void minix_write_inode(struct inode * inode)
{
  struct buffer_head *bh;
  bh = minix_update_inode(inode);
  brelse(bh);
}
// 回写inode到硬盘
int minix_sync_inode(struct inode * inode)
{
  int err = 0;
  struct buffer_head *bh;
  // 回写
  bh = minix_update_inode(inode);
  // 上面的回写是等待线程定期回写的,失败的话自己调驱动层直接回写
  if (bh && bh->b_dirt)
  {  
    // 驱动层会锁住buffer
    ll_rw_block(WRITE, 1, &bh);
    wait_on_buffer(bh);
    if (bh->b_req && !bh->b_uptodate)
    {
      printk ("IO error syncing minix inode [%04x:%08lx]\n",
        inode->i_dev, inode->i_ino);
      err = -1;
    }
  }
  else if (!bh)
    err = -1;
  brelse (bh);
  return err;
}

#ifdef MODULE

char kernel_version[] = UTS_RELEASE;

static struct file_system_type minix_fs_type = {
  minix_read_super, "minix", 1, NULL
};
// 支持以模块加载
int init_module(void)
{  
  // 注册文件系统
  register_filesystem(&minix_fs_type);
  return 0;
}
// 卸载模块
void cleanup_module(void)
{
  unregister_filesystem(&minix_fs_type);
}

#endif

本文分享自微信公众号 - 编程杂技(theanarkh)

原文出处及转载信息见文内详细说明,如有侵权,请联系 yunjia_community@tencent.com 删除。

原始发表时间:2019-07-10

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