super.c

讲述linux的初始化过程

	/* N.B. after this point bh must be released */
got_root:
	root_block = s->u.affs_sb.s_root_block;

	s->u.affs_sb.s_partition_size   = size;
	s->s_blocksize_bits             = blocksize == 512 ? 9 :
					  blocksize == 1024 ? 10 :
					  blocksize == 2048 ? 11 : 12;

	/* Find out which kind of FS we have */
	bb = affs_bread(dev,0,s->s_blocksize);
	if (!bb)
		goto out_no_root_block;
	chksum = be32_to_cpu(*(u32 *)bb->b_data);
	affs_brelse(bb);

	/* Dircache filesystems are compatible with non-dircache ones
	 * when reading. As long as they aren't supported, writing is
	 * not recommended.
	 */
	if ((chksum == FS_DCFFS || chksum == MUFS_DCFFS || chksum == FS_DCOFS
	     || chksum == MUFS_DCOFS) && !(s->s_flags & MS_RDONLY)) {
		printk(KERN_NOTICE "AFFS: Dircache FS - mounting %s read only\n",
			kdevname(dev));
		s->s_flags |= MS_RDONLY;
		s->u.affs_sb.s_flags |= SF_READONLY;
	}
	switch (chksum) {
		case MUFS_FS:
		case MUFS_INTLFFS:
			s->u.affs_sb.s_flags |= SF_MUFS;
			/* fall thru */
		case FS_INTLFFS:
			s->u.affs_sb.s_flags |= SF_INTL;
			break;
		case MUFS_DCFFS:
		case MUFS_FFS:
			s->u.affs_sb.s_flags |= SF_MUFS;
			break;
		case FS_DCFFS:
		case FS_FFS:
			break;
		case MUFS_OFS:
			s->u.affs_sb.s_flags |= SF_MUFS;
			/* fall thru */
		case FS_OFS:
			s->u.affs_sb.s_flags |= SF_OFS;
			s->s_flags |= MS_NOEXEC;
			break;
		case MUFS_DCOFS:
		case MUFS_INTLOFS:
			s->u.affs_sb.s_flags |= SF_MUFS;
		case FS_DCOFS:
		case FS_INTLOFS:
			s->u.affs_sb.s_flags |= SF_INTL | SF_OFS;
			s->s_flags |= MS_NOEXEC;
			break;
		default:
			goto out_unknown_fs;
	}

	if (mount_flags & SF_VERBOSE) {
		chksum = cpu_to_be32(chksum);
		printk(KERN_NOTICE "AFFS: Mounting volume \"%*s\": Type=%.3s\\%c, Blocksize=%d\n",
			GET_END_PTR(struct root_end,bh->b_data,blocksize)->disk_name[0],
			&GET_END_PTR(struct root_end,bh->b_data,blocksize)->disk_name[1],
			(char *)&chksum,((char *)&chksum)[3] + '0',blocksize);
	}

	s->s_flags |= MS_NODEV | MS_NOSUID;

	/* Keep super block in cache */
	bb = affs_bread(dev,root_block,s->s_blocksize);
	if (!bb)
		goto out_no_root_block;
	s->u.affs_sb.s_root_bh = bb;
	/* N.B. after this point s_root_bh must be released */

	/* Allocate space for bitmaps, zones and others */

	size   = s->u.affs_sb.s_partition_size - reserved;
	num_bm = (size + s->s_blocksize * 8 - 32 - 1) / (s->s_blocksize * 8 - 32);
	az_no  = (size + AFFS_ZONE_SIZE - 1) / (AFFS_ZONE_SIZE - 32);
	ptype  = num_bm * sizeof(struct affs_bm_info) +
		 az_no * sizeof(struct affs_alloc_zone) +
		 MAX_ZONES * sizeof(struct affs_zone);
	pr_debug("AFFS: num_bm=%d, az_no=%d, sum=%d\n",num_bm,az_no,ptype);
	if (!(s->u.affs_sb.s_bitmap = kmalloc(ptype, GFP_KERNEL)))
		goto out_no_bitmap;
	memset(s->u.affs_sb.s_bitmap,0,ptype);
	/* N.B. after the point s_bitmap must be released */

	s->u.affs_sb.s_zones   = (struct affs_zone *)&s->u.affs_sb.s_bitmap[num_bm];
	s->u.affs_sb.s_alloc   = (struct affs_alloc_zone *)&s->u.affs_sb.s_zones[MAX_ZONES];
	s->u.affs_sb.s_num_az  = az_no;

	mapidx = 0;

	if (ROOT_END_S(bh->b_data,s)->bm_flag == 0) {
		if (!(s->s_flags & MS_RDONLY)) {
			printk(KERN_NOTICE "AFFS: Bitmap invalid - mounting %s read only\n",
				kdevname(dev));
			s->s_flags |= MS_RDONLY;
		}
		affs_brelse(bh);
		bh = NULL;
		goto nobitmap;
	}

	/* The following section is ugly, I know. Especially because of the
	 * reuse of some variables that are not named properly.
	 */

	key    = root_block;
	ptype  = s->s_blocksize / 4 - 49;
	stype  = ptype + 25;
	offset = s->u.affs_sb.s_reserved;
	az_no  = 0;
	while (bh) {
		bm = (u32 *)bh->b_data;
		for (i = ptype; i < stype && bm[i]; i++, mapidx++) {
			if (mapidx >= num_bm) {
				printk(KERN_ERR "AFFS: Extraneous bitmap pointer - "
					       "mounting %s read only.\n",kdevname(dev));
				s->s_flags |= MS_RDONLY;
				s->u.affs_sb.s_flags |= SF_READONLY;
				continue;
			}
			bb = affs_bread(dev,be32_to_cpu(bm[i]),s->s_blocksize);
			if (!bb)
				goto out_no_read_bm;
			if (affs_checksum_block(s->s_blocksize,bb->b_data,NULL,NULL) &&
			    !(s->s_flags & MS_RDONLY)) {
				printk(KERN_WARNING "AFFS: Bitmap (%d,key=%u) invalid - "
				       "mounting %s read only.\n",mapidx,be32_to_cpu(bm[i]),
					kdevname(dev));
				s->s_flags |= MS_RDONLY;
				s->u.affs_sb.s_flags |= SF_READONLY;
			}
			/* Mark unused bits in the last word as allocated */
			if (size <= s->s_blocksize * 8 - 32) {	/* last bitmap */
				ptype = size / 32 + 1;		/* word number */
				key   = size & 0x1F;		/* used bits */
				if (key && !(s->s_flags & MS_RDONLY)) {
					chksum = cpu_to_be32(0x7FFFFFFF >> (31 - key));
					((u32 *)bb->b_data)[ptype] &= chksum;
					affs_fix_checksum(s->s_blocksize,bb->b_data,0);
					mark_buffer_dirty(bb);
					bmalt = 1;
				}
				ptype = (size + 31) & ~0x1F;
				size  = 0;
				s->u.affs_sb.s_flags |= SF_BM_VALID;
			} else {
				ptype = s->s_blocksize * 8 - 32;
				size -= ptype;
			}
			s->u.affs_sb.s_bitmap[mapidx].bm_firstblk = offset;
			s->u.affs_sb.s_bitmap[mapidx].bm_bh       = NULL;
			s->u.affs_sb.s_bitmap[mapidx].bm_key      = be32_to_cpu(bm[i]);
			s->u.affs_sb.s_bitmap[mapidx].bm_count    = 0;
			offset += ptype;

			for (j = 0; ptype > 0; j++, az_no++, ptype -= key) {
				key = MIN(ptype,AFFS_ZONE_SIZE);	/* size in bits */
				s->u.affs_sb.s_alloc[az_no].az_size = key / 32;
				s->u.affs_sb.s_alloc[az_no].az_free =
					affs_count_free_bits(key / 8,bb->b_data +
					     j * (AFFS_ZONE_SIZE / 8) + 4);
			}
			affs_brelse(bb);
		}
		key   = be32_to_cpu(bm[stype]);		/* Next block of bitmap pointers	*/
		ptype = 0;
		stype = s->s_blocksize / 4 - 1;
		affs_brelse(bh);
		bh = NULL;
		if (key) {
			bh = affs_bread(dev,key,s->s_blocksize);
			if (!bh)
				goto out_no_bm_ext;
		}
	}
	if (mapidx < num_bm)
		goto out_bad_num;

nobitmap:
	s->u.affs_sb.s_bm_count = num_bm;

	/* set up enough so that it can read an inode */

	s->s_dirt  = 1;
	root_inode = iget(s,root_block);
	if (!root_inode)
		goto out_no_root;
	s->s_root  = d_alloc_root(root_inode);
	if (!s->s_root)
		goto out_no_root;
	s->s_root->d_op = &affs_dentry_operations;

	/* Record date of last change if the bitmap was truncated and
	 * create data zones if the volume is writable.
	 */

	if (!(s->s_flags & MS_RDONLY)) {
		if (bmalt) {
			secs_to_datestamp(CURRENT_TIME,&ROOT_END(
				s->u.affs_sb.s_root_bh->b_data,root_inode)->disk_altered);
			affs_fix_checksum(s->s_blocksize,s->u.affs_sb.s_root_bh->b_data,5);
			mark_buffer_dirty(s->u.affs_sb.s_root_bh);
		}
		affs_make_zones(s);
	}

	pr_debug("AFFS: s_flags=%lX\n",s->s_flags);
	return s;

out_bad_opts:
	printk(KERN_ERR "AFFS: Error parsing options\n");
	goto out_fail;
out_bad_size:
	printk(KERN_ERR "AFFS: Could not determine device size\n");
	goto out_free_prefix;
out_no_valid_block:
	if (!silent)
		printk(KERN_ERR "AFFS: No valid root block on device %s\n",
			kdevname(dev));
	goto out_restore;
out_unknown_fs:
	printk(KERN_ERR "AFFS: Unknown filesystem on device %s: %08X\n",
		kdevname(dev), chksum);
	goto out_free_bh;
out_no_root_block:
	printk(KERN_ERR "AFFS: Cannot read root block\n");
	goto out_free_bh;
out_no_bitmap:
	printk(KERN_ERR "AFFS: Bitmap allocation failed\n");
	goto out_free_root_block;
out_no_read_bm:
	printk(KERN_ERR "AFFS: Cannot read bitmap\n");
	goto out_free_bitmap;
out_no_bm_ext:
	printk(KERN_ERR "AFFS: Cannot read bitmap extension\n");
	goto out_free_bitmap;
out_bad_num:
	printk(KERN_ERR "AFFS: Got only %d bitmap blocks, expected %d\n",
		mapidx, num_bm);
	goto out_free_bitmap;
out_no_root:
	printk(KERN_ERR "AFFS: Get root inode failed\n");

	/*
	 * Begin the cascaded cleanup ...
	 */
	iput(root_inode);
out_free_bitmap:
	kfree(s->u.affs_sb.s_bitmap);
out_free_root_block:
	affs_brelse(s->u.affs_sb.s_root_bh);
out_free_bh:
	affs_brelse(bh);
out_restore:
	set_blocksize(dev, s->u.affs_sb.s_blksize);
out_free_prefix:
	if (s->u.affs_sb.s_prefix)
		kfree(s->u.affs_sb.s_prefix);
out_fail:
	return NULL;
}

static int
affs_remount(struct super_block *sb, int *flags, char *data)
{
	int			 blocksize;
	uid_t			 uid;
	gid_t			 gid;
	int			 mode;
	int			 reserved;
	int			 root_block;
	unsigned long		 mount_flags;
	unsigned long		 read_only = sb->u.affs_sb.s_flags & SF_READONLY;

	pr_debug("AFFS: remount(flags=0x%x,opts=\"%s\")\n",*flags,data);

	if (!parse_options(data,&uid,&gid,&mode,&reserved,&root_block,
	    &blocksize,&sb->u.affs_sb.s_prefix,sb->u.affs_sb.s_volume,&mount_flags))
		return -EINVAL;
	sb->u.affs_sb.s_flags = mount_flags | read_only;
	sb->u.affs_sb.s_mode  = mode;
	sb->u.affs_sb.s_uid   = uid;
	sb->u.affs_sb.s_gid   = gid;

	if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY))
		return 0;
	if (*flags & MS_RDONLY) {
		sb->s_dirt = 1;
		while (sb->s_dirt)
			affs_write_super(sb);
		sb->s_flags |= MS_RDONLY;
	} else if (!(sb->u.affs_sb.s_flags & SF_READONLY)) {
		sb->s_flags &= ~MS_RDONLY;
		affs_make_zones(sb);
	} else {
		affs_warning(sb,"remount","Cannot remount fs read/write because of errors");
		return -EINVAL;
	}
	return 0;
}

static int
affs_statfs(struct super_block *sb, struct statfs *buf)
{
	int		 free;

	pr_debug("AFFS: statfs() partsize=%d, reserved=%d\n",sb->u.affs_sb.s_partition_size,
	     sb->u.affs_sb.s_reserved);

	free          = affs_count_free_blocks(sb);
	buf->f_type    = AFFS_SUPER_MAGIC;
	buf->f_bsize   = sb->s_blocksize;
	buf->f_blocks  = sb->u.affs_sb.s_partition_size - sb->u.affs_sb.s_reserved;
	buf->f_bfree   = free;
	buf->f_bavail  = free;
	return 0;
}

static DECLARE_FSTYPE_DEV(affs_fs_type, "affs", affs_read_super);

static int __init init_affs_fs(void)
{
	return register_filesystem(&affs_fs_type);
}

static void __exit exit_affs_fs(void)
{
	unregister_filesystem(&affs_fs_type);
}

EXPORT_NO_SYMBOLS;

module_init(init_affs_fs)
module_exit(exit_affs_fs)