Ext2文件系统 inode

void ext2_read_inode (struct inode * inode)
{
struct buffer_head * bh;
struct ext2_inode * raw_inode;
unsigned long block_group;
unsigned long group_desc;
unsigned long desc;
unsigned long block;
unsigned long offset;
struct ext2_group_desc * gdp;

if ((inode->i_ino != EXT2_ROOT_INO
&& inode->i_ino != EXT2_ACL_IDX_INO
&& inode->i_ino != EXT2_ACL_DATA_INO && inode->i_ino < EXT2_FIRST_INO(inode->i_sb))
|| inode->i_ino > le32_to_cpu(inode->i_sb->u.ext2_sb.s_es->s_inodes_count))
{
ext2_error (inode->i_sb, "ext2_read_inode",
"bad inode number: %lu", inode->i_ino);
goto bad_inode;
}
//块组号
block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
if (block_group >= inode->i_sb->u.ext2_sb.s_groups_count) {
ext2_error (inode->i_sb, "ext2_read_inode",
"group >= groups count");
goto bad_inode;
}
//对于该块组描述符所在的逻辑块号
group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(inode->i_sb);
//该inode对应的块组描述符在该逻辑块中的偏移
desc = block_group & (EXT2_DESC_PER_BLOCK(inode->i_sb) - 1);
bh = inode->i_sb->u.ext2_sb.s_group_desc[group_desc];
if (!bh) {
ext2_error (inode->i_sb, "ext2_read_inode",
"Descriptor not loaded");
goto bad_inode;
}

gdp = (struct ext2_group_desc *) bh->b_data;
/*
* Figure out the offset within the block group inode table
*/
//该inode在该块组中，相对于inode节点起始地址的偏移
offset = ((inode->i_ino - 1) % EXT2_INODES_PER_GROUP(inode->i_sb)) *
EXT2_INODE_SIZE(inode->i_sb);
/*块组描述符.bg_inode_table:　Block number of first inode table block,即inode节点表的起始逻辑块号，所以off需要除以块大小，1K
*/
block = le32_to_cpu(gdp[desc].bg_inode_table) +
(offset >> EXT2_BLOCK_SIZE_BITS(inode->i_sb));
if (!(bh = sb_bread(inode->i_sb, block))) {
ext2_error (inode->i_sb, "ext2_read_inode",
"unable to read inode block - "
"inode=%lu, block=%lu", inode->i_ino, block);
goto bad_inode;
}
/*由于sb_bread已经把inode所在的逻辑块block读入到bh中，所以offset应是相对于该块起始地址的偏移，即offset如下
*/
offset &= (EXT2_BLOCK_SIZE(inode->i_sb) - 1);
raw_inode = (struct ext2_inode *) (bh->b_data + offset);

inode->i_mode = le16_to_cpu(raw_inode->i_mode);
inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
if(!(test_opt (inode->i_sb, NO_UID32))) {
inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
}
inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
inode->i_size = le32_to_cpu(raw_inode->i_size);
inode->i_atime = le32_to_cpu(raw_inode->i_atime);
inode->i_ctime = le32_to_cpu(raw_inode->i_ctime);
inode->i_mtime = le32_to_cpu(raw_inode->i_mtime);
inode->u.ext2_i.i_dtime = le32_to_cpu(raw_inode->i_dtime);
/* We now have enough fields to check if the inode was active or not.
* This is needed because nfsd might try to access dead inodes
* the test is that same one that e2fsck uses
* NeilBrown 1999oct15
*/
if (inode->i_nlink == 0 && (inode->i_mode == 0 || inode->u.ext2_i.i_dtime)) {
/* this inode is deleted */
brelse (bh);
goto bad_inode;
}
inode->i_blksize = PAGE_SIZE;   /* This is the optimal IO size (for stat), not the fs block size */
inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);
inode->i_version = ++event;
inode->u.ext2_i.i_flags = le32_to_cpu(raw_inode->i_flags);
inode->u.ext2_i.i_faddr = le32_to_cpu(raw_inode->i_faddr);
inode->u.ext2_i.i_frag_no = raw_inode->i_frag;
inode->u.ext2_i.i_frag_size = raw_inode->i_fsize;
inode->u.ext2_i.i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
if (S_ISREG(inode->i_mode))
inode->i_size |= ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
else
inode->u.ext2_i.i_dir_acl = le32_to_cpu(raw_inode->i_dir_acl);
inode->i_generation = le32_to_cpu(raw_inode->i_generation);
inode->u.ext2_i.i_prealloc_count = 0;
inode->u.ext2_i.i_block_group = block_group;

/*
* NOTE! The in-memory inode i_data array is in little-endian order
* even on big-endian machines: we do NOT byteswap the block numbers!
*/
for (block = 0; block < EXT2_N_BLOCKS; block++)
inode->u.ext2_i.i_data[block] = raw_inode->i_block[block];

if (inode->i_ino == EXT2_ACL_IDX_INO ||
inode->i_ino == EXT2_ACL_DATA_INO)
/* Nothing to do */ ;
else if (S_ISREG(inode->i_mode)) {
inode->i_op = &ext2_file_inode_operations;
inode->i_fop = &ext2_file_operations;
inode->i_mapping->a_ops = &ext2_aops;
} else if (S_ISDIR(inode->i_mode)) {
inode->i_op = &ext2_dir_inode_operations;
inode->i_fop = &ext2_dir_operations;
inode->i_mapping->a_ops = &ext2_aops;
} else if (S_ISLNK(inode->i_mode)) {
if (!inode->i_blocks)
inode->i_op = &ext2_fast_symlink_inode_operations;
else {
inode->i_op = &page_symlink_inode_operations;
inode->i_mapping->a_ops = &ext2_aops;
}
} else
init_special_inode(inode, inode->i_mode,
le32_to_cpu(raw_inode->i_block[0]));
brelse (bh);
inode->i_attr_flags = 0;
if (inode->u.ext2_i.i_flags & EXT2_SYNC_FL) {
inode->i_attr_flags |= ATTR_FLAG_SYNCRONOUS;
inode->i_flags |= S_SYNC;
}
if (inode->u.ext2_i.i_flags & EXT2_APPEND_FL) {
inode->i_attr_flags |= ATTR_FLAG_APPEND;
inode->i_flags |= S_APPEND;
}
if (inode->u.ext2_i.i_flags & EXT2_IMMUTABLE_FL) {
inode->i_attr_flags |= ATTR_FLAG_IMMUTABLE;
inode->i_flags |= S_IMMUTABLE;
}
if (inode->u.ext2_i.i_flags & EXT2_NOATIME_FL) {
inode->i_attr_flags |= ATTR_FLAG_NOATIME;
inode->i_flags |= S_NOATIME;
}
return;

bad_inode:
make_bad_inode(inode);
return;
}