linux-kernel - [PATCH 3.16 169/245] hidraw: Return EPOLLOUT from hidraw

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Date:   Fri, 24 Apr 2020 00:06:36 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jiri Kosina" <jkosina@...e.cz>,
        "Fabian Henneke" <fabian.henneke@...il.com>
Subject: [PATCH 3.16 169/245] hidraw: Return EPOLLOUT from hidraw_poll

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Fabian Henneke <fabian.henneke@...il.com>

commit 378b80370aa1fe50f9c48a3ac8af3e416e73b89f upstream.

Always return EPOLLOUT from hidraw_poll when a device is connected.
This is safe since writes are always possible (but will always block).

hidraw does not support non-blocking writes and instead always calls
blocking backend functions on write requests. Hence, so far, a call to
poll never returned EPOLLOUT, which confuses tools like socat.

Signed-off-by: Fabian Henneke <fabian.henneke@...il.com>
In-reply-to: <CA+hv5qkyis03CgYTWeWX9cr0my-d2Oe+aZo+mjmWRXgjrGqyrw@...l.gmail.com>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
[bwh: Backported to 3.16: s/EPOLL/POLL/]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/hid/hidraw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -265,7 +265,7 @@ static unsigned int hidraw_poll(struct f
 
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
-		return POLLIN | POLLRDNORM;
+		return POLLIN | POLLRDNORM | POLLOUT;
 	if (!list->hidraw->exist)
 		return POLLERR | POLLHUP;
 	return 0;