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From:   "Matthew Wilcox (Oracle)" <willy@infradead.org>
To:     linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, andy.rudoff@intel.com
Cc:     Rao Shoaib <rao.shoaib@oracle.com>,
        Matthew Wilcox <willy@infradead.org>
Subject: [PATCH] af_unix: Allow Unix sockets to raise SIGURG
Date:   Fri, 22 Jan 2021 15:06:37 +0000
Message-Id: <20210122150638.210444-1-willy@infradead.org>
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From: Rao Shoaib <rao.shoaib@oracle.com>

TCP sockets allow SIGURG to be sent to the process holding the other
end of the socket.  Extend Unix sockets to have the same ability.

The API is the same in that the sender uses sendmsg() with MSG_OOB to
raise SIGURG.  Unix sockets behave in the same way as TCP sockets with
SO_OOBINLINE set.

SIGURG is ignored by default, so applications which do not know about this
feature will be unaffected.  In addition to installing a SIGURG handler,
the receiving application must call F_SETOWN or F_SETOWN_EX to indicate
which process or thread should receive the signal.

Signed-off-by: Rao Shoaib <rao.shoaib@oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 net/unix/af_unix.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 41c3303c3357..849dff688c2c 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1837,8 +1837,6 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 		return err;
 
 	err = -EOPNOTSUPP;
-	if (msg->msg_flags&MSG_OOB)
-		goto out_err;
 
 	if (msg->msg_namelen) {
 		err = sk->sk_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
@@ -1903,6 +1901,9 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 		sent += size;
 	}
 
+	if (msg->msg_flags & MSG_OOB)
+		sk_send_sigurg(other);
+
 	scm_destroy(&scm);
 
 	return sent;
-- 
2.29.2