inode.c

对minix代码进行注释

/*
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Copyright (C) 1996  Gertjan van Wingerde    ([e-mail])
 *	Minix V2 fs support.
 *
 *  Modified for 680x0 by Andreas Schwab
 */

#include <linux/module.h>
#include "minix.h"
#include <linux/buffer_head.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/highuid.h>
#include <linux/vfs.h>

static void minix_read_inode(struct inode * inode);
static int minix_write_inode(struct inode * inode, int wait);
static int minix_statfs(struct dentry *dentry, struct kstatfs *buf);
static int minix_remount (struct super_block * sb, int * flags, char * data);

static void minix_delete_inode(struct inode *inode)
{
	truncate_inode_pages(&inode->i_data, 0);
	//从位移0开始将所有页截去
	inode->i_size = 0;
	minix_truncate(inode);
	minix_free_inode(inode);
}

static void minix_put_super(struct super_block *sb)
{
	int i;
	struct minix_sb_info *sbi = minix_sb(sb);

	if (!(sb->s_flags & MS_RDONLY)) {
		sbi->s_ms->s_state = sbi->s_mount_state;
		mark_buffer_dirty(sbi->s_sbh);
	}
	for (i = 0; i < sbi->s_imap_blocks; i++)
		brelse(sbi->s_imap[i]);
	//将超级块中的inode位图释放
	for (i = 0; i < sbi->s_zmap_blocks; i++)
		brelse(sbi->s_zmap[i]);
	//将超级块中的数据块位图释放(表示空闲与否)
	brelse (sbi->s_sbh);
	kfree(sbi->s_imap);
	sb->s_fs_info = NULL;
	kfree(sbi);

	return;
}

static kmem_cache_t * minix_inode_cachep;

static struct inode *minix_alloc_inode(struct super_block *sb)
{
	struct minix_inode_info *ei;
	ei = (struct minix_inode_info *)kmem_cache_alloc(minix_inode_cachep, SLAB_KERNEL);
	//从高速缓存描述符中获得新对象
	if (!ei)
		return NULL;
	return &ei->vfs_inode;
}

static void minix_destroy_inode(struct inode *inode)
{
	kmem_cache_free(minix_inode_cachep, minix_i(inode));
	//释放一个对象
}

static void init_once(void * foo, kmem_cache_t * cachep, unsigned long flags)
{
	struct minix_inode_info *ei = (struct minix_inode_info *) foo;

	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
	    SLAB_CTOR_CONSTRUCTOR)
		inode_init_once(&ei->vfs_inode);
}
 
static int init_inodecache(void)
{
	minix_inode_cachep = kmem_cache_create("minix_inode_cache",
					     sizeof(struct minix_inode_info),
					     0, (SLAB_RECLAIM_ACCOUNT|
						SLAB_MEM_SPREAD),
					     init_once, NULL);
	if (minix_inode_cachep == NULL)
		return -ENOMEM;
	return 0;
}

static void destroy_inodecache(void)
{
	if (kmem_cache_destroy(minix_inode_cachep))
		printk(KERN_INFO "minix_inode_cache: not all structures were freed\n");
}

static struct super_operations minix_sops = {
	.alloc_inode	= minix_alloc_inode,
	.destroy_inode	= minix_destroy_inode,
	.read_inode	= minix_read_inode,
	.write_inode	= minix_write_inode,
	.delete_inode	= minix_delete_inode,
	.put_super	= minix_put_super,
	.statfs		= minix_statfs,
	.remount_fs	= minix_remount,
};

static int minix_remount (struct super_block * sb, int * flags, char * data)
{
	struct minix_sb_info * sbi = minix_sb(sb);
	struct minix_super_block * ms;

	ms = sbi->s_ms;
	if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY))
		return 0;
	if (*flags & MS_RDONLY) {
		if (ms->s_state & MINIX_VALID_FS ||
		    !(sbi->s_mount_state & MINIX_VALID_FS))
			return 0;
		/* Mounting a rw partition read-only. */
		ms->s_state = sbi->s_mount_state;
		mark_buffer_dirty(sbi->s_sbh);
	} else {
	  	/* Mount a partition which is read-only, read-write. */
		sbi->s_mount_state = ms->s_state;
		ms->s_state &= ~MINIX_VALID_FS;
		mark_buffer_dirty(sbi->s_sbh);

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

static int minix_fill_super(struct super_block *s, void *data, int silent)
{
	//访问磁盘上的超级块，填充超级块对象

	struct buffer_head *bh;
	struct buffer_head **map;
	struct minix_super_block *ms;
	int i, block;
	struct inode *root_inode;
	struct minix_sb_info *sbi;

	sbi = kmalloc(sizeof(struct minix_sb_info), GFP_KERNEL);
	//分配超级块对象的内存
	if (!sbi)
		return -ENOMEM;
	s->s_fs_info = sbi;
	//s:磁盘上的超级块
	memset(sbi, 0, sizeof(struct minix_sb_info));

	/* N.B. These should be compile-time tests.
	   Unfortunately that is impossible. */
	if (32 != sizeof (struct minix_inode))
		panic("bad V1 i-node size");
	if (64 != sizeof(struct minix2_inode))
		panic("bad V2 i-node size");

	if (!sb_set_blocksize(s, BLOCK_SIZE))
		goto out_bad_hblock;

	if (!(bh = sb_bread(s, 1)))
		goto out_bad_sb;
	//将磁盘的第一块读入到bh中

	ms = (struct minix_super_block *) bh->b_data;
	//ms指向bh中的数据
	sbi->s_ms = ms;
	sbi->s_sbh = bh;
	sbi->s_mount_state = ms->s_state;
	sbi->s_ninodes = ms->s_ninodes;
	sbi->s_nzones = ms->s_nzones;
	sbi->s_imap_blocks = ms->s_imap_blocks;
	sbi->s_zmap_blocks = ms->s_zmap_blocks;
	sbi->s_firstdatazone = ms->s_firstdatazone;
	sbi->s_log_zone_size = ms->s_log_zone_size;
	sbi->s_max_size = ms->s_max_size;
	s->s_magic = ms->s_magic;
	if (s->s_magic == MINIX_SUPER_MAGIC) {
		sbi->s_version = MINIX_V1;
		sbi->s_dirsize = 16;
		sbi->s_namelen = 14;
		sbi->s_link_max = MINIX_LINK_MAX;
	} else if (s->s_magic == MINIX_SUPER_MAGIC2) {
		sbi->s_version = MINIX_V1;
		sbi->s_dirsize = 32;
		sbi->s_namelen = 30;
		sbi->s_link_max = MINIX_LINK_MAX;
	} else if (s->s_magic == MINIX2_SUPER_MAGIC) {
		sbi->s_version = MINIX_V2;
		sbi->s_nzones = ms->s_zones;
		sbi->s_dirsize = 16;
		sbi->s_namelen = 14;
		sbi->s_link_max = MINIX2_LINK_MAX;
	} else if (s->s_magic == MINIX2_SUPER_MAGIC2) {
		sbi->s_version = MINIX_V2;
		sbi->s_nzones = ms->s_zones;
		sbi->s_dirsize = 32;
		sbi->s_namelen = 30;
		sbi->s_link_max = MINIX2_LINK_MAX;
	} else
		goto out_no_fs;

	/*
	 * Allocate the buffer map to keep the superblock small.
	 */
	if (sbi->s_imap_blocks == 0 || sbi->s_zmap_blocks == 0)
		goto out_illegal_sb;
	i = (sbi->s_imap_blocks + sbi->s_zmap_blocks) * sizeof(bh);
	map = kmalloc(i, GFP_KERNEL);
	if (!map)
		goto out_no_map;
	memset(map, 0, i);
	sbi->s_imap = &map[0];
	sbi->s_zmap = &map[sbi->s_imap_blocks];

	block=2;
	//从第二块开始读
	for (i=0 ; i < sbi->s_imap_blocks ; i++) {
		if (!(sbi->s_imap[i]=sb_bread(s, block)))
			goto out_no_bitmap;
		block++;
	}
	//顺序将inode影射表读入
	for (i=0 ; i < sbi->s_zmap_blocks ; i++) {
		if (!(sbi->s_zmap[i]=sb_bread(s, block)))
			goto out_no_bitmap;
		block++;
	}
	//顺序将磁盘块影射表读入

	minix_set_bit(0,sbi->s_imap[0]->b_data);
	minix_set_bit(0,sbi->s_zmap[0]->b_data);
	//设置后面一个指针的第0位

	/* set up enough so that it can read an inode */
	s->s_op = &minix_sops;
	root_inode = iget(s, MINIX_ROOT_INO);
	//获得root inode，即第一个inode
	if (!root_inode || is_bad_inode(root_inode))
		goto out_no_root;

	s->s_root = d_alloc_root(root_inode);
	//allocate root dentry 
	if (!s->s_root)
		goto out_iput;

	if (!NO_TRUNCATE)
		s->s_root->d_op = &minix_dentry_operations;
	//设置目录项操作函数

	if (!(s->s_flags & MS_RDONLY)) {
		ms->s_state &= ~MINIX_VALID_FS;
		mark_buffer_dirty(bh);
		//设置bh为脏
	}
	if (!(sbi->s_mount_state & MINIX_VALID_FS))
		printk("MINIX-fs: mounting unchecked file system, "
			"running fsck is recommended\n");
 	else if (sbi->s_mount_state & MINIX_ERROR_FS)
		printk("MINIX-fs: mounting file system with errors, "
			"running fsck is recommended\n");
	return 0;

out_iput:
	iput(root_inode);
	goto out_freemap;

out_no_root:
	if (!silent)
		printk("MINIX-fs: get root inode failed\n");
	goto out_freemap;

out_no_bitmap:
	printk("MINIX-fs: bad superblock or unable to read bitmaps\n");
out_freemap:
	for (i = 0; i < sbi->s_imap_blocks; i++)
		brelse(sbi->s_imap[i]);
	for (i = 0; i < sbi->s_zmap_blocks; i++)
		brelse(sbi->s_zmap[i]);
	kfree(sbi->s_imap);
	goto out_release;

out_no_map:
	if (!silent)
		printk("MINIX-fs: can't allocate map\n");
	goto out_release;

out_illegal_sb:
	if (!silent)
		printk("MINIX-fs: bad superblock\n");
	goto out_release;

out_no_fs:
	if (!silent)
		printk("VFS: Can't find a Minix or Minix V2 filesystem "
			"on device %s\n", s->s_id);
out_release:
	brelse(bh);
	goto out;

out_bad_hblock:
	printk("MINIX-fs: blocksize too small for device\n");
	goto out;

out_bad_sb:
	printk("MINIX-fs: unable to read superblock\n");
out:
	s->s_fs_info = NULL;
	kfree(sbi);
	return -EINVAL;
}