tree f6bc7f43c964c3d045c104de054de5b0b83bacdf
parent 9356b535fcb71db494fc434acceb79f56d15bda2
author Peter Hurley <peter@hurleysoftware.com> 1371302065 -0400
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1374622981 -0700

n_tty: Replace canon_data with index comparison

canon_data represented the # of lines which had been copied
to the receive buffer but not yet copied to the user buffer.
The value was tested to determine if input was available in
canonical mode (and also to force input overrun if the
receive buffer was full but a newline had not been received).

However, the actual count was irrelevent; only whether it was
non-zero (meaning 'is there any input to transfer?'). This
shared count is unnecessary and unsafe with a lockless algorithm.
The same check is made by comparing canon_head with read_tail instead.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>