TOMOYO: Copy directly to userspace buffer.

When userspace program reads policy from /sys/kernel/security/tomoyo/
interface, TOMOYO uses line buffered mode. A line has at least one word.

Commit 006dacc "TOMOYO: Support longer pathname." changed a word's max length
from 4000 bytes to max kmalloc()able bytes. By that commit, a line's max length
changed from 8192 bytes to more than max kmalloc()able bytes.

Max number of words in a line remains finite. This patch changes the way of
buffering so that all words in a line are firstly directly copied to userspace
buffer as much as possible and are secondly queued for next read request.
Words queued are guaranteed to be valid until /sys/kernel/security/tomoyo/
interface is close()d.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>