From: Wei Wang <weiwan@xxxxxxxxxx> TCP_FASTOPEN socket option was added by: commit 8336886f786fdacbc19b719c1f7ea91eb70706d4 TCP_FASTOPEN_CONNECT socket option was added by the following patch series: commit 065263f40f0972d5f1cd294bb0242bd5aa5f06b2 commit 25776aa943401662617437841b3d3ea4693ee98a commit 19f6d3f3c8422d65b5e3d2162e30ef07c6e21ea2 commit 3979ad7e82dfe3fb94a51c3915e64ec64afa45c3 Add detailed description for these 2 options Signed-off-by: Wei Wang <weiwan@xxxxxxxxxx> --- man7/tcp.7 | 90 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) diff --git a/man7/tcp.7 b/man7/tcp.7 index 529246145..c03aa60db 100644 --- a/man7/tcp.7 +++ b/man7/tcp.7 @@ -1149,6 +1149,96 @@ Bound the size of the advertised window to this value. The kernel imposes a minimum size of SOCK_MIN_RCVBUF/2. This option should not be used in code intended to be portable. +.TP +.BR TCP_FASTOPEN " (since Linux 3.6)" +This option enables Fast Open on the listener socket. The option value +specifies the PendingFastOpenRequests threshold, i.e. the maximum length +of pending SYNs with data payload. Once enabled, the TCP implementation +will respond with TCP Fast Open cookies per request. +.TP +.BR TCP_FASTOPEN_CONNECT " (since Linux 4.11)" +This option enables an alternative way to perform Fast Open on the active +side (client). +When this option is enabled, +.BR connect (2) +would behave differently depending if a Fast Open cookie is available for +the destination. + +If a cookie is not available (i.e. first contact to the destination), +.BR connect (2) +behaves as usual by sending a SYN immediately, except the SYN would include +an empty Fast Open cookie option to solicit a cookie. + +If a cookie is available, +.BR connect (2) +would return 0 immediately but the SYN transmission is defered. A subsequent +.BR write (2) +or +.BR sendmsg (2) +would trigger a SYN with data plus cookie in the Fast Open option. In other +words, the actual connect operation is deferred until data is supplied. + +While this option is designed for convenience, enabling it does change the +behaviors and might return new errnos of socket calls: + s = socket() + Create a new socket + setsockopt(s, IPPROTO_TCP, TCP_FASTOPEN_CONNECT, ...) + Set this option + connect() + With cookie present, return 0 immediately. + With no cookie, initiate 3WHS with Fast Open option empty and return +.B EINPROGRESS + write()/sendmsg() + With cookie present and +.BR connect (2) +called ahead, send out SYN with data plus cookie in the Fast Open option +and return the number of bytes buffered. + With no cookie and 3 WHS not yet completed, return +.B EINPROGRESS. + No +.B MSG_FASTOPEN +flag is needed. + + read() + Return +.B EWOULDBLOCK +/ +.B EAGAIN +if 3WHS is not yet completed. + Return +.B EWOULDBLOCK +/ +.B EAGAIN +if connection is established but no message has been received. + Return number of bytes read if connection is established and message + has been received. + +.B Note: + With cookie present, +.BR write (2) +/ +.BR sendmsg (2) +must be called right after +.BR connect (2) +in order to send out SYN+data to complete 3WHS and establish connection. + Calling +.BR read (2) +right after +.BR connect (2) +without +.BR write (2) +will cause the blocking socket to be blocked forever. + +Here is the typical call flow with this new option: + s = socket(); + setsockopt(s, IPPROTO_TCP, TCP_FASTOPEN_CONNECT, 1, ...); + connect(s); + write(s); // write() should always follow connect() in order to + // trigger SYN to go out + read(s)/write(s); + ... + close(s); + .SS Sockets API TCP provides limited support for out-of-band data, in the form of (a single byte of) urgent data. -- 2.11.0.483.g087da7b7c-goog -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
