[PATCH 4/7] xfs: split direct IO write path from xfs_file_aio_write

[Christoph Hellwig]

> +STATIC ssize_t
> +xfs_file_dio_aio_write(
> +	struct kiocb		*iocb,
> +	const struct iovec	*iovp,
> +	unsigned long		nr_segs,
> +	loff_t			pos,
> +	size_t			ocount,
> +	int			*need_i_mutex,
> +	int			*iolock)

need_i_mutex == 1 is equivalent to iolock == XFS_IOLOCK_EXCL, I think
it's a good idea to throw in a patch to remove the need_i_mutex variable
before this patch.

Maybe that patch can even add xfs_rw_lock or similar helpers to
manipulate the i_mutex, the iolock, and the iolock variable together?

Speaking of that, shouldn't xfs_file_aio_read also take the iolock
exclusive during the page invalidation and then demote it, just like
the write case?  The above helpers would enforce that nicely.

> +	if ((pos & target->bt_smask) || (count & target->bt_smask))
> +		return XFS_ERROR(-EINVAL);

For the error traps to work this needs to be

	-XFS_ERROR(EINVAL);