ext2文件系统源代码之xattr.c

今天我们来看ext2的扩展属性的主要文件xattr.c，内部有扩展属性的最重要的代码实现，但是文件也真的很长，我们来开始吧。

/* 作者版权信息 * linux/fs/ext2/xattr.c * * Copyright (C) 2001-2003 Andreas Gruenbacher <[e-mail]> * 被Harrison Xing修改过 * Fix by Harrison Xing <[e-mail]>. * Extended attributes for symlinks and special files added per *  suggestion of Luka Renko <[e-mail]>. * xattr consolidation Copyright (c) 2004 James Morris <[e-mail]>, *  Red Hat Inc. * */#include <linux/buffer_head.h>#include <linux/module.h>#include <linux/init.h>#include <linux/slab.h>#include <linux/mbcache.h>#include <linux/quotaops.h>#include <linux/rwsem.h>#include "ext2.h"#include "xattr.h"#include "acl.h"/*宏定义，参数是buffer_head就诶勾踢指针，得到ext2_xattr_header类型的指针，指向buffer的头部*/#define HDR(bh) ((struct ext2_xattr_header *)((bh)->b_data))/*将指针转化为ext2_xattr_entry类型的*/#define ENTRY(ptr) ((struct ext2_xattr_entry *)(ptr))/*获得buffer的第一个项指针*/#define FIRST_ENTRY(bh) ENTRY(HDR(bh)+1)/*判断当前的项是不是最后一个*/#define IS_LAST_ENTRY(entry) (*(__u32 *)(entry) == 0)/*调试信息*/#ifdef EXT2_XATTR_DEBUG# define ea_idebug(inode, f...) do { \printk(KERN_DEBUG "inode %s:%ld: ", \inode->i_sb->s_id, inode->i_ino); \printk(f); \printk("\n"); \} while (0)# define ea_bdebug(bh, f...) do { \char b[BDEVNAME_SIZE]; \printk(KERN_DEBUG "block %s:%lu: ", \bdevname(bh->b_bdev, b), \(unsigned long) bh->b_blocknr); \printk(f); \printk("\n"); \} while (0)#else# define ea_idebug(f...)# define ea_bdebug(f...)#endif/*一些用到的函数声明*/static int ext2_xattr_set2(struct inode *, struct buffer_head *,   struct ext2_xattr_header *);static int ext2_xattr_cache_insert(struct buffer_head *);static struct buffer_head *ext2_xattr_cache_find(struct inode *, struct ext2_xattr_header *);static void ext2_xattr_rehash(struct ext2_xattr_header *,      struct ext2_xattr_entry *);/*系统存储的属性缓存*/static struct mb_cache *ext2_xattr_cache;/*属性的名称和处理函数的映射*/static struct xattr_handler *ext2_xattr_handler_map[] = {[EXT2_XATTR_INDEX_USER]     = &ext2_xattr_user_handler,#ifdef CONFIG_EXT2_FS_POSIX_ACL[EXT2_XATTR_INDEX_POSIX_ACL_ACCESS]  = &ext2_xattr_acl_access_handler,[EXT2_XATTR_INDEX_POSIX_ACL_DEFAULT] = &ext2_xattr_acl_default_handler,#endif[EXT2_XATTR_INDEX_TRUSTED]     = &ext2_xattr_trusted_handler,#ifdef CONFIG_EXT2_FS_SECURITY[EXT2_XATTR_INDEX_SECURITY]     = &ext2_xattr_security_handler,#endif};/*扩展属性的集合*/struct xattr_handler *ext2_xattr_handlers[] = {&ext2_xattr_user_handler,&ext2_xattr_trusted_handler,#ifdef CONFIG_EXT2_FS_POSIX_ACL&ext2_xattr_acl_access_handler,&ext2_xattr_acl_default_handler,#endif#ifdef CONFIG_EXT2_FS_SECURITY&ext2_xattr_security_handler,#endifNULL};/*由扩展属性在数组里的下表，获得对应的处理函数结构体，参数name_index就是下表*/static inline struct xattr_handler *ext2_xattr_handler(int name_index){struct xattr_handler *handler = NULL;/*如果参数合法，返回对应的结构体*/if (name_index > 0 && name_index < ARRAY_SIZE(ext2_xattr_handler_map))/*上边刚说过的结构体*/handler = ext2_xattr_handler_map[name_index];return handler;}/*ext2_xattr_get()函数，复制一个扩展属性结构体到一个给定的buffer里，或者是计算需要的buffer大小，参数buffer如果是NULL的话，就计算需要的buffer大小，当失败的时候返回负的错误编号，成功时候返回消耗的字节数目*/intext2_xattr_get(struct inode *inode, int name_index, const char *name,       void *buffer, size_t buffer_size){struct buffer_head *bh = NULL;struct ext2_xattr_entry *entry;size_t name_len, size;char *end;int error;/*调试信息，不管了*/ea_idebug(inode, "name=%d.%s, buffer=%p, buffer_size=%ld",  name_index, name, buffer, (long)buffer_size);/*如果要求的属性名称为NULL，说明传入参数有问题*/if (name == NULL)return -EINVAL;/*读i_file_acl之前必须上锁*/down_read(&EXT2_I(inode)->xattr_sem);error = -ENODATA;/*i_file_acl指向属性的文件块号，如果为空，直接返回*/if (!EXT2_I(inode)->i_file_acl)goto cleanup;ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);/*读取这个块进入内存*/bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);error = -EIO;if (!bh)goto cleanup;ea_bdebug(bh, "b_count=%d, refcount=%d",atomic_read(&(bh->b_count)), le32_to_cpu(HDR(bh)->h_refcount));/*end指向buffer的末尾*/end = bh->b_data + bh->b_size;/*检查读取的缓冲区，看看这个块是不是坏块*/if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||    HDR(bh)->h_blocks != cpu_to_le32(1)) {    /*如果是坏块，报错并返回IO错误*/bad_block:ext2_error(inode->i_sb, "ext2_xattr_get","inode %ld: bad block %d", inode->i_ino,EXT2_I(inode)->i_file_acl);error = -EIO;goto cleanup;}/* 根据属性的名字寻找这个属性 *//*先获得属性名字长度*/name_len = strlen(name);error = -ERANGE;/*最大名字长度是255*/if (name_len > 255)goto cleanup;/*获得属性的第一项*/entry = FIRST_ENTRY(bh);/*遍历属性的每一项*/while (!IS_LAST_ENTRY(entry)) {struct ext2_xattr_entry *next =EXT2_XATTR_NEXT(entry);/*检验当前项是不是合法*/if ((char *)next >= end)goto bad_block;/*匹配，是不是我们想要的*/if (name_index == entry->e_name_index &&    name_len == entry->e_name_len &&    memcmp(name, entry->e_name, name_len) == 0)goto found;entry = next;}/* 检查余下的项，看看有没有坏的 */while (!IS_LAST_ENTRY(entry)) {struct ext2_xattr_entry *next =EXT2_XATTR_NEXT(entry);if ((char *)next >= end)goto bad_block;entry = next;}/*创建一个新的扩展属性项，并且插入它*/if (ext2_xattr_cache_insert(bh))ea_idebug(inode, "cache insert failed");error = -ENODATA;goto cleanup;found:/* 检查保存value的块号，否则说明这个块是坏的 */if (entry->e_value_block != 0)goto bad_block;size = le32_to_cpu(entry->e_value_size);/*检查块的大小是否合法*/if (size > inode->i_sb->s_blocksize ||    le16_to_cpu(entry->e_value_offs) + size > inode->i_sb->s_blocksize)goto bad_block;/*创建一个新的扩展属性项，并且插入到缓冲区*/if (ext2_xattr_cache_insert(bh))ea_idebug(inode, "cache insert failed");if (buffer) {error = -ERANGE;if (size > buffer_size)goto cleanup;/* 返回属性 */memcpy(buffer, bh->b_data + le16_to_cpu(entry->e_value_offs),size);}error = size;cleanup:/*释放资源的引用*/brelse(bh);up_read(&EXT2_I(inode)->xattr_sem);return error;}/*ext2_xattr_list()函数，复制一系列的属性到buffer里，当buffer是NULL的时候就只计算需要的字节数，成功返回需要的字节数，失败返回错误码 */static intext2_xattr_list(struct inode *inode, char *buffer, size_t buffer_size){struct buffer_head *bh = NULL;struct ext2_xattr_entry *entry;char *end;size_t rest = buffer_size;int error;ea_idebug(inode, "buffer=%p, buffer_size=%ld",  buffer, (long)buffer_size);/*在读取i_file_acl之前必须上xattr_sem锁*/down_read(&EXT2_I(inode)->xattr_sem);error = 0;/*检查i_file_acl是不是为空*/if (!EXT2_I(inode)->i_file_acl)goto cleanup;ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);/*从硬盘上读取这个属性所在的块*/bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);error = -EIO;if (!bh)goto cleanup;ea_bdebug(bh, "b_count=%d, refcount=%d",atomic_read(&(bh->b_count)), le32_to_cpu(HDR(bh)->h_refcount));/*end指向缓冲区的末尾*/end = bh->b_data + bh->b_size;/*检验缓冲区是不是合法*/if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||    HDR(bh)->h_blocks != cpu_to_le32(1)) {    /*坏块，打印信息，返回IO错误*/bad_block:ext2_error(inode->i_sb, "ext2_xattr_list","inode %ld: bad block %d", inode->i_ino,EXT2_I(inode)->i_file_acl);error = -EIO;goto cleanup;}/* 检查得到的buffer里的数据结构是不是对的 *//*第一个项*/entry = FIRST_ENTRY(bh);/*遍历每一个项*/while (!IS_LAST_ENTRY(entry)) {struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(entry);if ((char *)next >= end)goto bad_block;entry = next;}/*创建一个新的项并插入*/if (ext2_xattr_cache_insert(bh))ea_idebug(inode, "cache insert failed");/* 列出所有的属性名称 */for (entry = FIRST_ENTRY(bh); !IS_LAST_ENTRY(entry);     entry = EXT2_XATTR_NEXT(entry)) {     /*得到属性处理结构体*/struct xattr_handler *handler =ext2_xattr_handler(entry->e_name_index);if (handler) {/*调用这个结构体的函数list来列出所有的属性*/size_t size = handler->list(inode, buffer, rest,    entry->e_name,    entry->e_name_len);/*检查函数是否成功*/if (buffer) {if (size > rest) {error = -ERANGE;goto cleanup;}buffer += size;}rest -= size;}}/*返回所占用的全部空间大小*/error = buffer_size - rest;  /* total size */cleanup:/*释放占用的全部空间*/brelse(bh);up_read(&EXT2_I(inode)->xattr_sem);return error;}/* 这个函数是从inode调用的listxattr()函数 */ssize_text2_listxattr(struct dentry *dentry, char *buffer, size_t size){/*直接调用前边的函数*/return ext2_xattr_list(dentry->d_inode, buffer, size);}/* 如果EXT2_FEATURE_COMPAT_EXT_ATTR位没有设置，就设置了 */static void ext2_xattr_update_super_block(struct super_block *sb){if (EXT2_HAS_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR))return;EXT2_SET_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR);sb->s_dirt = 1;mark_buffer_dirty(EXT2_SB(sb)->s_sbh);}/*ext2_xattr_set()函数可以创建，替换，删除一个inode的扩展属性buffer是NULL就删除，不为NUll就是替换或者是创建一个属性，flags参数的值XATTR_REPLACE和XATTR_CREATE标记处扩展属性必须存在和必须不能存在，失败的时候返回负的错误号 */intext2_xattr_set(struct inode *inode, int name_index, const char *name,       const void *value, size_t value_len, int flags){struct super_block *sb = inode->i_sb;struct buffer_head *bh = NULL;struct ext2_xattr_header *header = NULL;struct ext2_xattr_entry *here, *last;size_t name_len, free, min_offs = sb->s_blocksize;int not_found = 1, error;char *end;ea_idebug(inode, "name=%d.%s, value=%p, value_len=%ld",  name_index, name, value, (long)value_len);/*参数检查*/if (value == NULL)value_len = 0;if (name == NULL)return -EINVAL;/*名字长度检查*/name_len = strlen(name);if (name_len > 255 || value_len > sb->s_blocksize)return -ERANGE;/*在对文件的i_file_acl字段读写之前，必须上锁*/down_write(&EXT2_I(inode)->xattr_sem);/*如果i_file_acl字段不为0*/if (EXT2_I(inode)->i_file_acl) {/* inode已经有一个扩展属性块了，读取这个块的内容 */bh = sb_bread(sb, EXT2_I(inode)->i_file_acl);error = -EIO;/*检查是否读取出错*/if (!bh)goto cleanup;ea_bdebug(bh, "b_count=%d, refcount=%d",atomic_read(&(bh->b_count)),le32_to_cpu(HDR(bh)->h_refcount));/*header指向头部*/header = HDR(bh);/*end指向尾部*/end = bh->b_data + bh->b_size;/*检查头部的数据，看这个缓冲区是不是对的*/if (header->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||    header->h_blocks != cpu_to_le32(1)) {bad_block:ext2_error(sb, "ext2_xattr_set","inode %ld: bad block %d", inode->i_ino,    EXT2_I(inode)->i_file_acl);error = -EIO;goto cleanup;}/* 寻找我们想要的属性 *//* 先把here指向第一个项 */here = FIRST_ENTRY(bh);/*遍历所有的项*/while (!IS_LAST_ENTRY(here)) {/*next指向下一个*/struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(here);/*检查这个块是不是坏块，好的应该是正好不会超出缓冲区的*/if ((char *)next >= end)goto bad_block;/*得到属性值在文件里的偏移量*/if (!here->e_value_block && here->e_value_size) {size_t offs = le16_to_cpu(here->e_value_offs);/*min_offs指向最小的偏移量*/if (offs < min_offs)min_offs = offs;}/*判定有没有找到我们想要的项，首先要name_index一致，另外名称长度和名字也要一致*/not_found = name_index - here->e_name_index;if (!not_found)not_found = name_len - here->e_name_len;if (!not_found)not_found = memcmp(name, here->e_name,name_len);if (not_found <= 0)break;/*指向下一个项*/here = next;}last = here;/* 计算还没有遍历的，是不是有不合法的数据，还要计算min_offs */while (!IS_LAST_ENTRY(last)) {struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(last);if ((char *)next >= end)goto bad_block;if (!last->e_value_block && last->e_value_size) {size_t offs = le16_to_cpu(last->e_value_offs);if (offs < min_offs)min_offs = offs;}last = next;}/* 看看是不是有多余的空间了. */free = min_offs - ((char*)last - (char*)header) - sizeof(__u32);} else {/* 这个块是坏的，我们需要一个新的块 */free = sb->s_blocksize -sizeof(struct ext2_xattr_header) - sizeof(__u32);here = last = NULL;  }if (not_found) {/* 请求删除的项没找到，返回错误 */error = -ENODATA;if (flags & XATTR_REPLACE)goto cleanup;error = 0;if (value == NULL)goto cleanup;} else {/* 创建一个已经存在的项吗 */error = -EEXIST;if (flags & XATTR_CREATE)goto cleanup;if (!here->e_value_block && here->e_value_size) {size_t size = le32_to_cpu(here->e_value_size);if (le16_to_cpu(here->e_value_offs) + size >     sb->s_blocksize || size > sb->s_blocksize)goto bad_block;free += EXT2_XATTR_SIZE(size);}free += EXT2_XATTR_LEN(name_len);}error = -ENOSPC;/*空间不够创建*/if (free < EXT2_XATTR_LEN(name_len) + EXT2_XATTR_SIZE(value_len))goto cleanup;/* 设置新属性. */if (header) {struct mb_cache_entry *ce;/*从ext2_xattr_cache获得一个缓冲区*/ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev,bh->b_blocknr);/*访问前上锁*/lock_buffer(bh);if (header->h_refcount == cpu_to_le32(1)) {ea_bdebug(bh, "modifying in-place");if (ce)mb_cache_entry_free(ce);} else {int offset;if (ce)mb_cache_entry_release(ce);unlock_buffer(bh);ea_bdebug(bh, "cloning");header = kmalloc(bh->b_size, GFP_KERNEL);error = -ENOMEM;if (header == NULL)goto cleanup;/*把原来缓冲区的内容放到新分配的header里*/memcpy(header, HDR(bh), bh->b_size);header->h_refcount = cpu_to_le32(1);/*offset是偏移，here指向项，last指向最后一个entry*/offset = (char *)here - bh->b_data;here = ENTRY((char *)header + offset);offset = (char *)last - bh->b_data;last = ENTRY((char *)header + offset);}} else {/* 创建缓冲区，建立新的block结构体 */header = kzalloc(sb->s_blocksize, GFP_KERNEL);error = -ENOMEM;if (header == NULL)goto cleanup;end = (char *)header + sb->s_blocksize;header->h_magic = cpu_to_le32(EXT2_XATTR_MAGIC);header->h_blocks = header->h_refcount = cpu_to_le32(1);last = here = ENTRY(header+1);}/* 修改属性. */if (not_found) {/* 插入新的属性名称 *//* 得到对应名称的项的字节大小size，rest是余下的大小 */size_t size = EXT2_XATTR_LEN(name_len);size_t rest = (char *)last - (char *)here;/*为新的属性腾出位置*/memmove((char *)here + size, here, rest);/*新的地方先初始化为0*/memset(here, 0, size);/*赋值*/here->e_name_index = name_index;here->e_name_len = name_len;memcpy(here->e_name, name, name_len);} else {/* 如果属性的值就存在本块内 */if (!here->e_value_block && here->e_value_size) {/*指向第一个值*/char *first_val = (char *)header + min_offs;size_t offs = le16_to_cpu(here->e_value_offs);char *val = (char *)header + offs;size_t size = EXT2_XATTR_SIZE(le32_to_cpu(here->e_value_size));/*如果新旧属性值长度一样*/if (size == EXT2_XATTR_SIZE(value_len)) {/* 直接替换*/here->e_value_size = cpu_to_le32(value_len);memset(val + size - EXT2_XATTR_PAD, 0,       EXT2_XATTR_PAD); /* Clear pad bytes. */memcpy(val, value, value_len);goto skip_replace;}/* 新旧属性长度不一样，移除旧的 */memmove(first_val + size, first_val, val - first_val);memset(first_val, 0, size);here->e_value_offs = 0;min_offs += size;/* 还要调整所有的偏移 */last = ENTRY(header+1);while (!IS_LAST_ENTRY(last)) {size_t o = le16_to_cpu(last->e_value_offs);if (!last->e_value_block && o < offs)last->e_value_offs =cpu_to_le16(o + size);last = EXT2_XATTR_NEXT(last);}}if (value == NULL) {/* 移除原有的属性名 */size_t size = EXT2_XATTR_LEN(name_len);last = ENTRY((char *)last - size);memmove(here, (char*)here + size,(char*)last - (char*)here);memset(last, 0, size);}}if (value != NULL) {/* 插入新的值 */here->e_value_size = cpu_to_le32(value_len);/*值不是空值的话*/if (value_len) {/*修改*/size_t size = EXT2_XATTR_SIZE(value_len);char *val = (char *)header + min_offs - size;here->e_value_offs =cpu_to_le16((char *)val - (char *)header);memset(val + size - EXT2_XATTR_PAD, 0,       EXT2_XATTR_PAD); /* Clear the pad bytes. */memcpy(val, value, value_len);}}skip_replace:if (IS_LAST_ENTRY(ENTRY(header+1))) {/* 这个块不是空的. */if (bh && header == HDR(bh))unlock_buffer(bh);  /* we were modifying in-place. */error = ext2_xattr_set2(inode, bh, NULL);} else {ext2_xattr_rehash(header, here);if (bh && header == HDR(bh))unlock_buffer(bh);  /* we were modifying in-place. */error = ext2_xattr_set2(inode, bh, header);}cleanup:/*释放对buffer_head的引用*/brelse(bh);if (!(bh && header == HDR(bh)))kfree(header);/*释放锁*/up_write(&EXT2_I(inode)->xattr_sem);return error;}/*ext2_xattr_set()函数的下一半，更新文件系统*/static intext2_xattr_set2(struct inode *inode, struct buffer_head *old_bh,struct ext2_xattr_header *header){struct super_block *sb = inode->i_sb;struct buffer_head *new_bh = NULL;int error;if (header) {/*在缓存里寻找header的项*/new_bh = ext2_xattr_cache_find(inode, header);/*如果找到了*/if (new_bh) {/*同一个*/if (new_bh == old_bh) {ea_bdebug(new_bh, "keeping this block");} else {/* The old block is released after updating   the inode.  */ea_bdebug(new_bh, "reusing block");error = -EDQUOT;if (DQUOT_ALLOC_BLOCK(inode, 1)) {unlock_buffer(new_bh);goto cleanup;}HDR(new_bh)->h_refcount = cpu_to_le32(1 +le32_to_cpu(HDR(new_bh)->h_refcount));ea_bdebug(new_bh, "refcount now=%d",le32_to_cpu(HDR(new_bh)->h_refcount));}unlock_buffer(new_bh);} else if (old_bh && header == HDR(old_bh)) {/* Keep this block. No need to lock the block as we   don't need to change the reference count. */new_bh = old_bh;get_bh(new_bh);ext2_xattr_cache_insert(new_bh);} else {/* We need to allocate a new block */int goal = le32_to_cpu(EXT2_SB(sb)->s_es->           s_first_data_block) +   EXT2_I(inode)->i_block_group *   EXT2_BLOCKS_PER_GROUP(sb);int block = ext2_new_block(inode, goal,   NULL, NULL, &error);if (error)goto cleanup;ea_idebug(inode, "creating block %d", block);new_bh = sb_getblk(sb, block);if (!new_bh) {ext2_free_blocks(inode, block, 1);error = -EIO;goto cleanup;}lock_buffer(new_bh);memcpy(new_bh->b_data, header, new_bh->b_size);set_buffer_uptodate(new_bh);unlock_buffer(new_bh);ext2_xattr_cache_insert(new_bh);ext2_xattr_update_super_block(sb);}/*new_bh脏了*/mark_buffer_dirty(new_bh);if (IS_SYNC(inode)) {sync_dirty_buffer(new_bh);error = -EIO;if (buffer_req(new_bh) && !buffer_uptodate(new_bh))goto cleanup;}}/*更新inode的i_file_acl字段，修改时间等*/EXT2_I(inode)->i_file_acl = new_bh ? new_bh->b_blocknr : 0;inode->i_ctime = CURRENT_TIME_SEC;/*是否需要同步*/if (IS_SYNC(inode)) {error = ext2_sync_inode (inode);if (error && error != -ENOSPC) {if (new_bh && new_bh != old_bh)DQUOT_FREE_BLOCK(inode, 1);goto cleanup;}} elsemark_inode_dirty(inode);error = 0;/*如果存在原有的块，并且我们已经不用了就释放*/if (old_bh && old_bh != new_bh) {struct mb_cache_entry *ce;/*找到他在缓存里的位置*/ce = mb_cache_entry_get(ext2_xattr_cache, old_bh->b_bdev,old_bh->b_blocknr);lock_buffer(old_bh);if (HDR(old_bh)->h_refcount == cpu_to_le32(1)) {/* 如果引用仅仅有一个，释放 */if (ce)mb_cache_entry_free(ce);ea_bdebug(old_bh, "freeing");ext2_free_blocks(inode, old_bh->b_blocknr, 1);/* We let our caller release old_bh, so we * need to duplicate the buffer before. */get_bh(old_bh);bforget(old_bh);} else {/* 减少引用计数 */HDR(old_bh)->h_refcount = cpu_to_le32(le32_to_cpu(HDR(old_bh)->h_refcount) - 1);if (ce)mb_cache_entry_release(ce);DQUOT_FREE_BLOCK(inode, 1);mark_buffer_dirty(old_bh);ea_bdebug(old_bh, "refcount now=%d",le32_to_cpu(HDR(old_bh)->h_refcount));}unlock_buffer(old_bh);}cleanup:brelse(new_bh);return error;}/* ext2_xattr_delete_inode()函数释放与inode相关的属性资源 */voidext2_xattr_delete_inode(struct inode *inode){struct buffer_head *bh = NULL;struct mb_cache_entry *ce;/*读i_file_acl之前都要上这个锁*/down_write(&EXT2_I(inode)->xattr_sem);if (!EXT2_I(inode)->i_file_acl)goto cleanup;/*读这个属性所在的块*/bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);/*如果读取出现错误*/if (!bh) {ext2_error(inode->i_sb, "ext2_xattr_delete_inode","inode %ld: block %d read error", inode->i_ino,EXT2_I(inode)->i_file_acl);goto cleanup;}ea_bdebug(bh, "b_count=%d", atomic_read(&(bh->b_count)));/*检验读取出来的buffer_head是不是有问题，是不是ext2文件系统的属性*/if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||    HDR(bh)->h_blocks != cpu_to_le32(1)) {ext2_error(inode->i_sb, "ext2_xattr_delete_inode","inode %ld: bad block %d", inode->i_ino,EXT2_I(inode)->i_file_acl);goto cleanup;}/*在ext2_xattr_cache缓存里寻找并删除*/ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev, bh->b_blocknr);lock_buffer(bh);/*引用计数为1就删除*/if (HDR(bh)->h_refcount == cpu_to_le32(1)) {if (ce)mb_cache_entry_free(ce);ext2_free_blocks(inode, EXT2_I(inode)->i_file_acl, 1);get_bh(bh);bforget(bh);unlock_buffer(bh);} else {/*递减引用计数*/HDR(bh)->h_refcount = cpu_to_le32(le32_to_cpu(HDR(bh)->h_refcount) - 1);if (ce)mb_cache_entry_release(ce);ea_bdebug(bh, "refcount now=%d",le32_to_cpu(HDR(bh)->h_refcount));unlock_buffer(bh);mark_buffer_dirty(bh);if (IS_SYNC(inode))sync_dirty_buffer(bh);DQUOT_FREE_BLOCK(inode, 1);}EXT2_I(inode)->i_file_acl = 0;cleanup:brelse(bh);up_write(&EXT2_I(inode)->xattr_sem);}/* ext2_xattr_put_super()当文件系统被卸载的时候调用 */voidext2_xattr_put_super(struct super_block *sb){mb_cache_shrink(sb->s_bdev);}/* ext2_xattr_cache_insert()函数在属性缓存里创建一个新的扩展属性项，不管它是不是已经在ext2_xattr_cache缓存里，成返回0 */static intext2_xattr_cache_insert(struct buffer_head *bh){/*插入缓存是需要hash来便于查找*/__u32 hash = le32_to_cpu(HDR(bh)->h_hash);struct mb_cache_entry *ce;int error;/*在ext2_xattr_cache分配缓存*/ce = mb_cache_entry_alloc(ext2_xattr_cache);if (!ce)return -ENOMEM;/*把这个ce插入*/error = mb_cache_entry_insert(ce, bh->b_bdev, bh->b_blocknr, &hash);/*插入失败，释放缓存*/if (error) {mb_cache_entry_free(ce);if (error == -EBUSY) {ea_bdebug(bh, "already in cache (%d cache entries)",atomic_read(&ext2_xattr_cache->c_entry_count));error = 0;}} else {ea_bdebug(bh, "inserting [%x] (%d cache entries)", (int)hash,  atomic_read(&ext2_xattr_cache->c_entry_count));mb_cache_entry_release(ce);}return error;}/* ext2_xattr_cmp()函数比较两个扩展属性块，当这两个一样时返回0，不一样返回1，有错误返回负数 */static intext2_xattr_cmp(struct ext2_xattr_header *header1,       struct ext2_xattr_header *header2){struct ext2_xattr_entry *entry1, *entry2;/*得到这两个缓冲区的head*/entry1 = ENTRY(header1+1);entry2 = ENTRY(header2+1);/*遍历开始*/while (!IS_LAST_ENTRY(entry1)) {/*第一个没有到结尾第二个到结尾了，说明不一样*/if (IS_LAST_ENTRY(entry2))return 1;/*比较*/if (entry1->e_hash != entry2->e_hash ||    entry1->e_name_index != entry2->e_name_index ||    entry1->e_name_len != entry2->e_name_len ||    entry1->e_value_size != entry2->e_value_size ||    memcmp(entry1->e_name, entry2->e_name, entry1->e_name_len))return 1;if (entry1->e_value_block != 0 || entry2->e_value_block != 0)return -EIO;/*比较value*/if (memcmp((char *)header1 + le16_to_cpu(entry1->e_value_offs),   (char *)header2 + le16_to_cpu(entry2->e_value_offs),   le32_to_cpu(entry1->e_value_size)))return 1;/*指向下一个*/entry1 = EXT2_XATTR_NEXT(entry1);entry2 = EXT2_XATTR_NEXT(entry2);}/*不一样*/if (!IS_LAST_ENTRY(entry2))return 1;return 0;}/*ext2_xattr_cache_find()函数，寻找一个标记的扩展属性块。成功的话返回找到的块的buffer_head，失败返回NULL*/static struct buffer_head *ext2_xattr_cache_find(struct inode *inode, struct ext2_xattr_header *header){__u32 hash = le32_to_cpu(header->h_hash);struct mb_cache_entry *ce;/*没有共享在hash里*/if (!header->h_hash)return NULL;  ea_idebug(inode, "looking for cached blocks [%x]", (int)hash);again:/*在ext2_xattr_cache缓存里一个一个的找*/ce = mb_cache_entry_find_first(ext2_xattr_cache, 0,       inode->i_sb->s_bdev, hash);/*寻找的循环*/while (ce) {struct buffer_head *bh;/*检验得到的是不是合法的*/if (IS_ERR(ce)) {if (PTR_ERR(ce) == -EAGAIN)goto again;break;}/*读取这一块进入内存*/bh = sb_bread(inode->i_sb, ce->e_block);/*如果IO读取出错*/if (!bh) {ext2_error(inode->i_sb, "ext2_xattr_cache_find","inode %ld: block %ld read error",inode->i_ino, (unsigned long) ce->e_block);} else {/*开始读取buffer_head*/lock_buffer(bh);/*一个缓冲区被引用太多次*/if (le32_to_cpu(HDR(bh)->h_refcount) >   EXT2_XATTR_REFCOUNT_MAX) {ea_idebug(inode, "block %ld refcount %d>%d",  (unsigned long) ce->e_block,  le32_to_cpu(HDR(bh)->h_refcount),  EXT2_XATTR_REFCOUNT_MAX);/*匹配*/} else if (!ext2_xattr_cmp(header, HDR(bh))) {ea_bdebug(bh, "b_count=%d",  atomic_read(&(bh->b_count)));mb_cache_entry_release(ce);return bh;}unlock_buffer(bh);brelse(bh);}/*继续找*/ce = mb_cache_entry_find_next(ce, 0, inode->i_sb->s_bdev, hash);}return NULL;}#define NAME_HASH_SHIFT 5#define VALUE_HASH_SHIFT 16/*ext2_xattr_hash_entry()计算这个扩展属性的hash值 */static inline void ext2_xattr_hash_entry(struct ext2_xattr_header *header, struct ext2_xattr_entry *entry){__u32 hash = 0;char *name = entry->e_name;int n;for (n=0; n < entry->e_name_len; n++) {hash = (hash << NAME_HASH_SHIFT) ^       (hash >> (8*sizeof(hash) - NAME_HASH_SHIFT)) ^       *name++;}if (entry->e_value_block == 0 && entry->e_value_size != 0) {__le32 *value = (__le32 *)((char *)header +le16_to_cpu(entry->e_value_offs));for (n = (le32_to_cpu(entry->e_value_size) +     EXT2_XATTR_ROUND) >> EXT2_XATTR_PAD_BITS; n; n--) {hash = (hash << VALUE_HASH_SHIFT) ^       (hash >> (8*sizeof(hash) - VALUE_HASH_SHIFT)) ^       le32_to_cpu(*value++);}}entry->e_hash = cpu_to_le32(hash);}#undef NAME_HASH_SHIFT#undef VALUE_HASH_SHIFT#define BLOCK_HASH_SHIFT 16/* * ext2_xattr_rehash()重新计算hash值 */static void ext2_xattr_rehash(struct ext2_xattr_header *header,      struct ext2_xattr_entry *entry){struct ext2_xattr_entry *here;__u32 hash = 0;ext2_xattr_hash_entry(header, entry);here = ENTRY(header+1);while (!IS_LAST_ENTRY(here)) {if (!here->e_hash) {/* Block is not shared if an entry's hash value == 0 */hash = 0;break;}hash = (hash << BLOCK_HASH_SHIFT) ^       (hash >> (8*sizeof(hash) - BLOCK_HASH_SHIFT)) ^       le32_to_cpu(here->e_hash);here = EXT2_XATTR_NEXT(here);}header->h_hash = cpu_to_le32(hash);}#undef BLOCK_HASH_SHIFT/*ext2属性初始化*/int __initinit_ext2_xattr(void){/*创建缓冲区*/ext2_xattr_cache = mb_cache_create("ext2_xattr", NULL,sizeof(struct mb_cache_entry) +sizeof(((struct mb_cache_entry *) 0)->e_indexes[0]), 1, 6);if (!ext2_xattr_cache)return -ENOMEM;return 0;}/*ext2属性退出销毁*/voidexit_ext2_xattr(void){mb_cache_destroy(ext2_xattr_cache);}