Callers currently have to round out the size of buffers to match the
aligment constraints of log iovecs and xlog_write(). They should not
need to know this detail, so introduce a new function to calculate
the iovec length (for use in ->iop_size implementations). Also
modify xlog_finish_iovec() to round up the length to the correct
alignment so the callers don't need to do this, either.
Convert the only user - inode forks - of this alignment rounding to
use the new interface.
Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Dave Chinner <david@fromorbit.com>