ext2文件系统源代码之xattr.c
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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 <[email protected]> * 被Harrison Xing修改过 * Fix by Harrison Xing <[email protected]>. * Extended attributes for symlinks and special files added per * suggestion of Luka Renko <[email protected]>. * xattr consolidation Copyright (c) 2004 James Morris <[email protected]>, * 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, #endif NULL }; /*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*/ int ext2_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 int ext2_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_t ext2_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 */ int ext2_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 int ext2_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; } } else mark_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 */ void ext2_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 */ void ext2_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 int ext2_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 int ext2_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 __init init_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*/ void exit_ext2_xattr(void) { mb_cache_destroy(ext2_xattr_cache); }
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