linux-kernel - [PATCH v2 7/7] tty: n_tty: fix SIGIO for output

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Message-Id: <1452404714-9295-8-git-send-email-peter@hurleysoftware.com>
Date:	Sat,  9 Jan 2016 21:45:14 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Johannes Stezenbach <js@...21.net>
Subject: [PATCH v2 7/7] tty: n_tty: fix SIGIO for output

According to fcntl(2), "a SIGIO signal is sent whenever input
or output becomes possible on that file descriptor", i.e.
after the output buffer was full and now has space for new data.
But in fact SIGIO is sent after every write.

n_tty_write() should set TTY_DO_WRITE_WAKEUP only when
not all data could be written to the buffer.

[pjh: Also fixes missed SIGIO if amt written just happens to be
[     amount still to write

Signed-off-by: Johannes Stezenbach <js@...21.net>
[pjh: minor patch edits and re-submit]

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/n_tty.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 5ae661c..fad365a 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2361,7 +2361,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
 	}
 break_out:
 	remove_wait_queue(&tty->write_wait, &wait);
-	if (b - buf != nr && tty->fasync)
+	if (nr && tty->fasync)
 		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 	up_read(&tty->termios_rwsem);
 	return (b - buf) ? b - buf : retval;
-- 
2.7.0