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) {
		/* assert(header == HDR(bh)); */
		lock_buffer(bh);
		if (header->h_refcount == cpu_to_le32(1)) {
			__u32 hash = le32_to_cpu(header->h_hash);

			ea_bdebug(bh, "modifying in-place");
			/*
			 * This must happen under buffer lock for
			 * ext2_xattr_set2() to reliably detect modified block
			 */
			mb2_cache_entry_delete_block(EXT2_SB(sb)->s_mb_cache,
						     hash, bh->b_blocknr);

			/* keep the buffer locked while modifying it. */
		} else {
			int offset;

			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;
}