From mboxrd@z Thu Jan  1 00:00:00 1970
From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH 1/2 v2] libext2fs: introduce lseek SEEK_DATA/HOLE
Date: Tue, 15 Jan 2013 13:55:09 -0500
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Cc: linux-ext4@vger.kernel.org, Zheng Liu <wenqing.lz@taobao.com>
To: Zheng Liu <gnehzuil.liu@gmail.com>
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On Mon, Jan 14, 2013 at 10:18:30PM +0800, Zheng Liu wrote:
> +static errcode_t ext2fs_file_llseek_data(ext2_file_t file, __u64 offset)
> +{
> +	int		ret_flags, flag = 1;
> +	ext2_filsys	fs = file->fs;
> +	errcode_t	retval;
> +
> +	/*
> +	 * If offset == EXT2_SEEK_OFFSET_INVALID, that means that
> +	 * the caller wants to find the data from file->pos.
> +	 */
> +	offset = offset != EXT2_SEEK_OFFSET_INVALID ? offset : file->pos;
> +	file->blockno = offset / fs->blocksize;
> +	while (file->blockno * fs->blocksize < EXT2_I_SIZE(&file->inode)) {
> +		retval = ext2fs_bmap2(fs, file->ino, &file->inode,
> +				      BMAP_BUFFER, 0, file->blockno,
> +				      &ret_flags, &file->physblock);

Using bmap will certainly work, although as an optimization we can do
much better for extents if we use the extents interface.  I won't
insist on this, though.  (We can always optimize this later).

       	  		     	 	- Ted