[PATCH] Introduce SEEK_DATA/SEEK_HOLE support V8

[Mark Tinguely]

On 02/17/12 07:16, Jeff Liu wrote:
> Hello,
>
> This is the revised patch according to Dave's comments for V7.
>
> Changes to V8:
> --------------
> 1. If there is an internal error raised at extent reading routine, just
> return it rather than ENXIO.
> 2. Add the commit message.
> 3. Remove the for(;;) loop since there is no continuous holes shown even
> if create a Petabyte sparse file with hole extent length longer than
> 32-bit.  Thanks Dave for helping verify that!
> 4. In xfs_seek_data(), s/len/end/, looks 'end' is more meaningful here
> to indicate the range of extents mapped.
> 5. Remove BUG() from xfs_seek_data() since xfs_bmapi_read() have found
> any corruption during the lookup, it should not occurred at all.
>
> Any comments are appreciated!
>
> Thanks,
> -Jeff
>
>
> Signed-off-by: Jie Liu<jeff.liu at oracle.com>
> ---
>   This patch adds lseek(2) SEEK_DATA/SEEK_HOLE functionality.

> +STATIC loff_t
> +xfs_seek_hole(
> +	struct file		*file,
> +	loff_t			start,
> +	u32			type)
> +{
> +	struct inode		*inode = file->f_mapping->host;
> +	struct xfs_inode	*ip = XFS_I(inode);
> +	struct xfs_mount	*mp = ip->i_mount;
> +	loff_t			uninitialized_var(offset);
> +	loff_t			holeoff;
> +	xfs_fsize_t		isize;
> +	xfs_fileoff_t		fsbno;
> +	uint			lock;
> +	int			error;
> +
> +	lock = xfs_ilock_map_shared(ip);
> +
> +	isize = i_size_read(inode);
> +	if (start>= isize) {
> +		error = ENXIO;
> +		goto out_unlock;
> +	}
> +
> +	fsbno = XFS_B_TO_FSBT(mp, start);
> +	error = xfs_bmap_first_unused(NULL, ip, 1,&fsbno, XFS_DATA_FORK);
> +	if (error)
> +		goto out_unlock;
> +
> +	holeoff = XFS_FSB_TO_B(mp, fsbno);
> +	if (holeoff<= start)
> +		offset = start;
> +	else
> +		offset = min_t(loff_t, holeoff, isize);
> +
> +	if (offset != file->f_pos)
> +		file->f_pos = offset;
> +
> +out_unlock:
> +	xfs_iunlock_map_shared(ip, lock);
> +
> +	if (error)
> +		return -error;
> +	return offset;
> +}

Sorry this got set aside. This is being dusted off for inclusion.

Refresh my memory, do we need a XFS_FORCED_SHUTDOWN test in
xfs_seek_hole()? In the earlier versions it was covered in the
xfs_bmapi_read().

A comment on the min_t() that the xfs_bmap_first_unused() could
return a value bigger than the isize if there are no more holes
may help the forgetful such as myself.

Otherwise it looks good.

Thank-you.

Mark Tinguely <tinguely at sgi.com>