/*
   * linux/fs/ext2/xattr.c
   *
   * Copyright (C) 2001-2003 Andreas Gruenbacher <agruen@suse.de>
   *
   * Fix by Harrison Xing <harrison@mountainviewdata.com>.
   * Extended attributes for symlinks and special files added per
   *  suggestion of Luka Renko <luka.renko@hermes.si>.
   * xattr consolidation Copyright (c) 2004 James Morris <jmorris@redhat.com>,
   *  Red Hat Inc.
   *
   */
  
  /*
   * Extended attributes are stored on disk blocks allocated outside of
   * any inode. The i_file_acl field is then made to point to this allocated
   * block. If all extended attributes of an inode are identical, these
   * inodes may share the same extended attribute block. Such situations
   * are automatically detected by keeping a cache of recent attribute block
   * numbers and hashes over the block's contents in memory.
   *
   *
   * Extended attribute block layout:
   *
   *   +------------------+
   *   | header           |
   *   | entry 1          | |
   *   | entry 2          | | growing downwards
   *   | entry 3          | v
   *   | four null bytes  |
   *   | . . .            |
   *   | value 1          | ^
   *   | value 3          | | growing upwards
   *   | value 2          | |
   *   +------------------+
   *
   * The block header is followed by multiple entry descriptors. These entry

   * descriptors are variable in size, and aligned to EXT2_XATTR_PAD

   * byte boundaries. The entry descriptors are sorted by attribute name,
   * so that two extended attribute blocks can be compared efficiently.
   *
   * Attribute values are aligned to the end of the block, stored in
   * no specific order. They are also padded to EXT2_XATTR_PAD byte
   * boundaries. No additional gaps are left between them.
   *
   * Locking strategy
   * ----------------
   * EXT2_I(inode)->i_file_acl is protected by EXT2_I(inode)->xattr_sem.
   * EA blocks are only changed if they are exclusive to an inode, so
   * holding xattr_sem also means that nothing but the EA block's reference
   * count will change. Multiple writers to an EA block are synchronized
   * by the bh lock. No more than a single bh lock is held at any time
   * to avoid deadlocks.
   */
  
  #include <linux/buffer_head.h>

  #include <linux/init.h>
  #include <linux/slab.h>
  #include <linux/mbcache.h>
  #include <linux/quotaops.h>
  #include <linux/rwsem.h>

  #include <linux/security.h>

  #include "ext2.h"
  #include "xattr.h"
  #include "acl.h"
  
  #define HDR(bh) ((struct ext2_xattr_header *)((bh)->b_data))
  #define ENTRY(ptr) ((struct ext2_xattr_entry *)(ptr))
  #define FIRST_ENTRY(bh) ENTRY(HDR(bh)+1)
  #define IS_LAST_ENTRY(entry) (*(__u32 *)(entry) == 0)
  
  #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("
  "); \
  	} 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("
  "); \
  	} while (0)
  #else
  # define ea_idebug(f...)
  # define ea_bdebug(f...)
  #endif
  
  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 *);
  
  static struct mb_cache *ext2_xattr_cache;

  static const 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
  };

  const 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
  };

  static inline const struct xattr_handler *

  ext2_xattr_handler(int name_index)
  {

  	const struct xattr_handler *handler = NULL;

  
  	if (name_index > 0 && name_index < ARRAY_SIZE(ext2_xattr_handler_map))
  		handler = ext2_xattr_handler_map[name_index];
  	return handler;
  }
  
  /*
   * ext2_xattr_get()
   *
   * Copy an extended attribute into the buffer
   * provided, or compute the buffer size required.
   * Buffer is NULL to compute the size of the buffer required.
   *
   * Returns a negative error number on failure, or the number of bytes
   * used / required on success.
   */
  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;
  
  	ea_idebug(inode, "name=%d.%s, buffer=%p, buffer_size=%ld",
  		  name_index, name, buffer, (long)buffer_size);
  
  	if (name == NULL)
  		return -EINVAL;

  	name_len = strlen(name);
  	if (name_len > 255)
  		return -ERANGE;

  	down_read(&EXT2_I(inode)->xattr_sem);
  	error = -ENODATA;
  	if (!EXT2_I(inode)->i_file_acl)
  		goto cleanup;
  	ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);
  	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 = bh->b_data + bh->b_size;
  	if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
  	    HDR(bh)->h_blocks != cpu_to_le32(1)) {
  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;
  	}

  	/* find named attribute */

  	entry = FIRST_ENTRY(bh);
  	while (!IS_LAST_ENTRY(entry)) {
  		struct ext2_xattr_entry *next =
  			EXT2_XATTR_NEXT(entry);
  		if ((char *)next >= end)
  			goto bad_block;
  		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;
  	}

  	if (ext2_xattr_cache_insert(bh))
  		ea_idebug(inode, "cache insert failed");
  	error = -ENODATA;
  	goto cleanup;
  found:
  	/* check the buffer size */
  	if (entry->e_value_block != 0)
  		goto bad_block;
  	size = le32_to_cpu(entry->e_value_size);
  	if (size > inode->i_sb->s_blocksize ||
  	    le16_to_cpu(entry->e_value_offs) + size > inode->i_sb->s_blocksize)
  		goto bad_block;
  
  	if (ext2_xattr_cache_insert(bh))
  		ea_idebug(inode, "cache insert failed");
  	if (buffer) {
  		error = -ERANGE;
  		if (size > buffer_size)
  			goto cleanup;
  		/* return value of attribute */
  		memcpy(buffer, bh->b_data + le16_to_cpu(entry->e_value_offs),
  			size);
  	}
  	error = size;
  
  cleanup:
  	brelse(bh);
  	up_read(&EXT2_I(inode)->xattr_sem);
  
  	return error;
  }
  
  /*
   * ext2_xattr_list()
   *
   * Copy a list of attribute names into the buffer
   * provided, or compute the buffer size required.
   * Buffer is NULL to compute the size of the buffer required.
   *
   * Returns a negative error number on failure, or the number of bytes
   * used / required on success.
   */
  static int

  ext2_xattr_list(struct dentry *dentry, char *buffer, size_t buffer_size)

  {

  	struct inode *inode = dentry->d_inode;

  	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);
  
  	down_read(&EXT2_I(inode)->xattr_sem);
  	error = 0;
  	if (!EXT2_I(inode)->i_file_acl)
  		goto cleanup;
  	ea_idebug(inode, "reading block %d", EXT2_I(inode)->i_file_acl);
  	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 = bh->b_data + bh->b_size;
  	if (HDR(bh)->h_magic != cpu_to_le32(EXT2_XATTR_MAGIC) ||
  	    HDR(bh)->h_blocks != cpu_to_le32(1)) {
  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;
  	}
  
  	/* check the on-disk data structure */
  	entry = FIRST_ENTRY(bh);
  	while (!IS_LAST_ENTRY(entry)) {
  		struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(entry);
  
  		if ((char *)next >= end)
  			goto bad_block;
  		entry = next;
  	}
  	if (ext2_xattr_cache_insert(bh))
  		ea_idebug(inode, "cache insert failed");
  
  	/* list the attribute names */
  	for (entry = FIRST_ENTRY(bh); !IS_LAST_ENTRY(entry);
  	     entry = EXT2_XATTR_NEXT(entry)) {

  		const struct xattr_handler *handler =

  			ext2_xattr_handler(entry->e_name_index);
  
  		if (handler) {

  			size_t size = handler->list(dentry, buffer, rest,

  						    entry->e_name,

  						    entry->e_name_len,
  						    handler->flags);

  			if (buffer) {
  				if (size > rest) {
  					error = -ERANGE;
  					goto cleanup;
  				}
  				buffer += size;
  			}
  			rest -= size;
  		}
  	}
  	error = buffer_size - rest;  /* total size */
  
  cleanup:
  	brelse(bh);
  	up_read(&EXT2_I(inode)->xattr_sem);
  
  	return error;
  }
  
  /*
   * Inode operation listxattr()
   *

   * dentry->d_inode->i_mutex: don't care

   */
  ssize_t
  ext2_listxattr(struct dentry *dentry, char *buffer, size_t size)
  {

  	return ext2_xattr_list(dentry, buffer, size);

  }
  
  /*
   * If the EXT2_FEATURE_COMPAT_EXT_ATTR feature of this file system is
   * not set, set it.
   */
  static void ext2_xattr_update_super_block(struct super_block *sb)
  {
  	if (EXT2_HAS_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR))
  		return;

  	spin_lock(&EXT2_SB(sb)->s_lock);

  	EXT2_SET_COMPAT_FEATURE(sb, EXT2_FEATURE_COMPAT_EXT_ATTR);

  	spin_unlock(&EXT2_SB(sb)->s_lock);

  	sb->s_dirt = 1;
  	mark_buffer_dirty(EXT2_SB(sb)->s_sbh);

  }
  
  /*
   * ext2_xattr_set()
   *

   * Create, replace or remove an extended attribute for this inode.  Value

   * is NULL to remove an existing extended attribute, and non-NULL to
   * either replace an existing extended attribute, or create a new extended
   * attribute. The flags XATTR_REPLACE and XATTR_CREATE
   * specify that an extended attribute must exist and must not exist
   * previous to the call, respectively.
   *
   * Returns 0, or a negative error number on failure.
   */
  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;
  	
  	/*
  	 * header -- Points either into bh, or to a temporarily
  	 *           allocated buffer.
  	 * here -- The named entry found, or the place for inserting, within
  	 *         the block pointed to by header.
  	 * last -- Points right after the last named entry within the block
  	 *         pointed to by header.
  	 * min_offs -- The offset of the first value (values are aligned
  	 *             towards the end of the block).
  	 * end -- Points right after the block pointed to by header.
  	 */
  	
  	ea_idebug(inode, "name=%d.%s, value=%p, value_len=%ld",
  		  name_index, name, value, (long)value_len);

  	if (value == NULL)
  		value_len = 0;
  	if (name == NULL)
  		return -EINVAL;
  	name_len = strlen(name);
  	if (name_len > 255 || value_len > sb->s_blocksize)
  		return -ERANGE;
  	down_write(&EXT2_I(inode)->xattr_sem);
  	if (EXT2_I(inode)->i_file_acl) {
  		/* The inode already has an extended attribute block. */
  		bh = sb_bread(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));
  		header = HDR(bh);
  		end = bh->b_data + bh->b_size;
  		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;
  		}
  		/* Find the named attribute. */
  		here = FIRST_ENTRY(bh);
  		while (!IS_LAST_ENTRY(here)) {
  			struct ext2_xattr_entry *next = EXT2_XATTR_NEXT(here);
  			if ((char *)next >= end)
  				goto bad_block;
  			if (!here->e_value_block && here->e_value_size) {
  				size_t offs = le16_to_cpu(here->e_value_offs);
  				if (offs < min_offs)
  					min_offs = offs;
  			}
  			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;
  			here = next;
  		}
  		last = here;
  		/* We still need to compute min_offs and last. */
  		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;
  		}
  
  		/* Check whether we have enough space left. */
  		free = min_offs - ((char*)last - (char*)header) - sizeof(__u32);
  	} else {
  		/* We will use a new extended attribute block. */
  		free = sb->s_blocksize -
  			sizeof(struct ext2_xattr_header) - sizeof(__u32);
  		here = last = NULL;  /* avoid gcc uninitialized warning. */
  	}
  
  	if (not_found) {
  		/* Request to remove a nonexistent attribute? */
  		error = -ENODATA;
  		if (flags & XATTR_REPLACE)
  			goto cleanup;
  		error = 0;
  		if (value == NULL)
  			goto cleanup;
  	} else {
  		/* Request to create an existing attribute? */
  		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;
  	if (free < EXT2_XATTR_LEN(name_len) + EXT2_XATTR_SIZE(value_len))
  		goto cleanup;
  
  	/* Here we know that we can set the new attribute. */
  
  	if (header) {
  		struct mb_cache_entry *ce;
  
  		/* assert(header == HDR(bh)); */
  		ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev,
  					bh->b_blocknr);
  		lock_buffer(bh);
  		if (header->h_refcount == cpu_to_le32(1)) {
  			ea_bdebug(bh, "modifying in-place");
  			if (ce)
  				mb_cache_entry_free(ce);
  			/* keep the buffer locked while modifying it. */
  		} 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;
  			memcpy(header, HDR(bh), bh->b_size);
  			header->h_refcount = cpu_to_le32(1);
  
  			offset = (char *)here - bh->b_data;
  			here = ENTRY((char *)header + offset);
  			offset = (char *)last - bh->b_data;
  			last = ENTRY((char *)header + offset);
  		}
  	} else {
  		/* Allocate a buffer where we construct the new block. */

  		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);
  	}
  
  	/* Iff we are modifying the block in-place, bh is locked here. */
  
  	if (not_found) {
  		/* Insert the new name. */
  		size_t size = EXT2_XATTR_LEN(name_len);
  		size_t rest = (char *)last - (char *)here;
  		memmove((char *)here + size, here, rest);
  		memset(here, 0, size);
  		here->e_name_index = name_index;
  		here->e_name_len = name_len;
  		memcpy(here->e_name, name, name_len);
  	} else {
  		if (!here->e_value_block && here->e_value_size) {
  			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));
  
  			if (size == EXT2_XATTR_SIZE(value_len)) {
  				/* The old and the new value have the same
  				   size. Just replace. */
  				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;
  			}
  
  			/* Remove the old value. */
  			memmove(first_val + size, first_val, val - first_val);
  			memset(first_val, 0, size);
  			here->e_value_offs = 0;
  			min_offs += size;
  
  			/* Adjust all value offsets. */
  			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) {
  			/* Remove the old name. */
  			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) {
  		/* Insert the new value. */
  		here->e_value_size = cpu_to_le32(value_len);
  		if (value_len) {
  			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))) {
  		/* This block is now empty. */
  		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:
  	brelse(bh);
  	if (!(bh && header == HDR(bh)))
  		kfree(header);
  	up_write(&EXT2_I(inode)->xattr_sem);
  
  	return error;
  }
  
  /*
   * Second half of ext2_xattr_set(): Update the file system.
   */
  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) {
  		new_bh = ext2_xattr_cache_find(inode, header);
  		if (new_bh) {
  			/* We found an identical block in the cache. */
  			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 = dquot_alloc_block(inode, 1);
  				if (error) {

  					unlock_buffer(new_bh);
  					goto cleanup;
  				}

  				le32_add_cpu(&HDR(new_bh)->h_refcount, 1);

  				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 */

  			ext2_fsblk_t goal = ext2_group_first_block_no(sb,
  						EXT2_I(inode)->i_block_group);

  			int block = ext2_new_block(inode, goal, &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);

  				mark_inode_dirty(inode);

  				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);
  		}
  		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;
  		}
  	}
  
  	/* Update the inode. */
  	EXT2_I(inode)->i_file_acl = new_bh ? new_bh->b_blocknr : 0;
  	inode->i_ctime = CURRENT_TIME_SEC;
  	if (IS_SYNC(inode)) {

  		error = sync_inode_metadata(inode, 1);

  		/* In case sync failed due to ENOSPC the inode was actually
  		 * written (only some dirty data were not) so we just proceed
  		 * as if nothing happened and cleanup the unused block */
  		if (error && error != -ENOSPC) {

  			if (new_bh && new_bh != old_bh) {
  				dquot_free_block_nodirty(inode, 1);
  				mark_inode_dirty(inode);
  			}

  			goto cleanup;
  		}
  	} else
  		mark_inode_dirty(inode);
  
  	error = 0;
  	if (old_bh && old_bh != new_bh) {
  		struct mb_cache_entry *ce;
  
  		/*
  		 * If there was an old block and we are no longer using it,
  		 * release the old block.
  		 */
  		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)) {
  			/* Free the old block. */
  			if (ce)
  				mb_cache_entry_free(ce);
  			ea_bdebug(old_bh, "freeing");
  			ext2_free_blocks(inode, old_bh->b_blocknr, 1);

  			mark_inode_dirty(inode);

  			/* We let our caller release old_bh, so we
  			 * need to duplicate the buffer before. */
  			get_bh(old_bh);
  			bforget(old_bh);
  		} else {
  			/* Decrement the refcount only. */

  			le32_add_cpu(&HDR(old_bh)->h_refcount, -1);

  			if (ce)
  				mb_cache_entry_release(ce);

  			dquot_free_block_nodirty(inode, 1);
  			mark_inode_dirty(inode);

  			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()
   *
   * Free extended attribute resources associated with this inode. This
   * is called immediately before an inode is freed.
   */
  void
  ext2_xattr_delete_inode(struct inode *inode)
  {
  	struct buffer_head *bh = NULL;
  	struct mb_cache_entry *ce;
  
  	down_write(&EXT2_I(inode)->xattr_sem);
  	if (!EXT2_I(inode)->i_file_acl)
  		goto cleanup;
  	bh = sb_bread(inode->i_sb, EXT2_I(inode)->i_file_acl);
  	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)));
  	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;
  	}
  	ce = mb_cache_entry_get(ext2_xattr_cache, bh->b_bdev, bh->b_blocknr);
  	lock_buffer(bh);
  	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 {

  		le32_add_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_nodirty(inode, 1);

  	}

  	EXT2_I(inode)->i_file_acl = 0;
  
  cleanup:
  	brelse(bh);
  	up_write(&EXT2_I(inode)->xattr_sem);
  }
  
  /*
   * ext2_xattr_put_super()
   *
   * This is called when a file system is unmounted.
   */
  void
  ext2_xattr_put_super(struct super_block *sb)
  {

  	mb_cache_shrink(sb->s_bdev);

  }
  
  
  /*
   * ext2_xattr_cache_insert()
   *
   * Create a new entry in the extended attribute cache, and insert
   * it unless such an entry is already in the cache.
   *
   * Returns 0, or a negative error number on failure.
   */
  static int
  ext2_xattr_cache_insert(struct buffer_head *bh)
  {
  	__u32 hash = le32_to_cpu(HDR(bh)->h_hash);
  	struct mb_cache_entry *ce;
  	int error;

  	ce = mb_cache_entry_alloc(ext2_xattr_cache, GFP_NOFS);

  	if (!ce)
  		return -ENOMEM;

  	error = mb_cache_entry_insert(ce, bh->b_bdev, bh->b_blocknr, hash);

  	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()
   *
   * Compare two extended attribute blocks for equality.
   *
   * Returns 0 if the blocks are equal, 1 if they differ, and
   * a negative error number on errors.
   */
  static int
  ext2_xattr_cmp(struct ext2_xattr_header *header1,
  	       struct ext2_xattr_header *header2)
  {
  	struct ext2_xattr_entry *entry1, *entry2;
  
  	entry1 = ENTRY(header1+1);
  	entry2 = ENTRY(header2+1);
  	while (!IS_LAST_ENTRY(entry1)) {
  		if (IS_LAST_ENTRY(entry2))
  			return 1;
  		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;
  		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;
  
  		entry1 = EXT2_XATTR_NEXT(entry1);
  		entry2 = EXT2_XATTR_NEXT(entry2);
  	}
  	if (!IS_LAST_ENTRY(entry2))
  		return 1;
  	return 0;
  }
  
  /*
   * ext2_xattr_cache_find()
   *
   * Find an identical extended attribute block.
   *
   * Returns a locked buffer head to the block found, or NULL if such
   * a block was not found or an error occurred.
   */
  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;
  
  	if (!header->h_hash)
  		return NULL;  /* never share */
  	ea_idebug(inode, "looking for cached blocks [%x]", (int)hash);
  again:

  	ce = mb_cache_entry_find_first(ext2_xattr_cache, inode->i_sb->s_bdev,
  				       hash);

  	while (ce) {
  		struct buffer_head *bh;
  
  		if (IS_ERR(ce)) {
  			if (PTR_ERR(ce) == -EAGAIN)
  				goto again;
  			break;
  		}
  
  		bh = sb_bread(inode->i_sb, ce->e_block);
  		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 {
  			lock_buffer(bh);
  			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);
  			} 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);
  		}

  		ce = mb_cache_entry_find_next(ce, inode->i_sb->s_bdev, hash);

  	}
  	return NULL;
  }
  
  #define NAME_HASH_SHIFT 5
  #define VALUE_HASH_SHIFT 16
  
  /*
   * ext2_xattr_hash_entry()
   *
   * Compute the hash of an extended attribute.
   */
  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()
   *
   * Re-compute the extended attribute hash value after an entry has changed.
   */
  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
  
  int __init
  init_ext2_xattr(void)
  {

  	ext2_xattr_cache = mb_cache_create("ext2_xattr", 6);

  	if (!ext2_xattr_cache)
  		return -ENOMEM;
  	return 0;
  }
  
  void
  exit_ext2_xattr(void)
  {
  	mb_cache_destroy(ext2_xattr_cache);
  }