Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 28 Apr 2005 18:34:51 +0800 | From | Bernard Blackham <> | Subject | Non-blocking sockets, connect(), and socket states |
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[previously sent to the allegedly dead netdev@oss.sgi.com]
Hi,
Through playing with tcpcp[1], I've found out about a quirk in the kernel's handling of non-blocking connection-based sockets. The sk_socket->state value can take on one of SS_FREE, SS_UNCONNECTED, SS_CONNECTING, SS_CONNECTED or SS_DISCONNECTING. On a standard *blocking*, connection-oriented socket (eg, TCP), after connect() returns, sk_socket->state will be SS_CONNECTED.
However, if the socket is placed into non-blocking mode before the connect() call, connect() returns immediately with EINPROGRESS, and the sk_socket->state is set to SS_CONNECTING. When the socket finally does connect, the application is notified via poll(), but the state remains as SS_CONNECTING (which causes issues for tcpcp, though doesn't appear to have any other externally visible implications).
Werner, the author of tcpcp, suggests that the application should call connect() on the socket a second time, after the successful connection, to force the sk_socket->state value to SS_CONNECTED.
Should it be the kernel's responsibility to set SS_CONNECTED when the connection is established? Or should I go file bugs and submit patches on all the applications that use non-blocking sockets and don't call connect() a second time?
Thanks in advance,
Bernard.
[1] http://tcpcp.sf.net/
-- Bernard Blackham <bernard at blackham dot com dot au> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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