On Fri, Sep 24, 2021 at 4:54 PM Wei Wang <weiwan@xxxxxxxxxx> wrote: > > 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. > Also add descriptions for /proc entry tcp_fastopen and tcp_fastopen_key. > > Signed-off-by: Wei Wang <weiwan@xxxxxxxxxx> > --- Hi Alex, Does this version look OK to you to apply? Let me know. Thanks. Wei > man7/tcp.7 | 125 +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 125 insertions(+) > > diff --git a/man7/tcp.7 b/man7/tcp.7 > index 0a7c61a37..bdd4a33ca 100644 > --- a/man7/tcp.7 > +++ b/man7/tcp.7 > @@ -423,6 +423,28 @@ option. > .\" Since 2.4.0-test7 > Enable RFC\ 2883 TCP Duplicate SACK support. > .TP > +.IR tcp_fastopen " (Bitmask; default: 0x1; since Linux 3.7)" > +Enables RFC\ 7413 Fast Open support. > +The flag is used as a bitmap with the following values: > +.RS > +.IP 0x1 > +Enables client side Fast Open support > +.IP 0x2 > +Enables server side Fast Open support > +.IP 0x4 > +Allows client side to transmit data in SYN without Fast Open option > +.IP 0x200 > +Allows server side to accept SYN data without Fast Open option > +.IP 0x400 > +Enables Fast Open on all listeners without > +.B TCP_FASTOPEN > +socket option > +.RE > +.TP > +.IR tcp_fastopen_key " (since Linux 3.7)" > +Set server side RFC\ 7413 Fast Open key to generate Fast Open cookie > +when server side Fast Open support is enabled. > +.TP > .IR tcp_ecn " (Integer; default: see below; since Linux 2.4)" > .\" Since 2.4.0-test7 > Enable RFC\ 3168 Explicit Congestion Notification. > @@ -1202,6 +1224,109 @@ 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 (RFC\ 7413) on the listener socket. > +The value specifies the maximum length of pending SYNs > +(similar to the backlog argument in > +.BR listen (2)). > +Once enabled, > +the listener socket grants the TCP Fast Open cookie on incoming > +SYN with TCP Fast Open option. > +.IP > +More importantly it accepts the data in SYN with a valid Fast Open cookie > +and responds SYN-ACK acknowledging both the data and the SYN sequence. > +.BR accept (2) > +returns a socket that is available for read and write when the handshake > +has not completed yet. > +Thus the data exchange can commence before the handshake completes. > +This option requires enabling the server-side support on sysctl > +.IR net.ipv4.tcp_fastopen > +(see above). > +For TCP Fast Open client-side support, > +see > +.BR send (2) > +.B MSG_FASTOPEN > +or > +.B TCP_FASTOPEN_CONNECT > +below. > +.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 on if a Fast Open cookie is available > +for the destination. > +.IP > +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. > +.IP > +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. > +.IP > +.B Note: > +While this option is designed for convenience, > +enabling it does change the behaviors and certain system calls might set > +different > +.I errno > +values. > +With cookie present, > +.BR write (2) > +or > +.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. > +.IP > +The application should either set > +.B TCP_FASTOPEN_CONNECT > +socket option before > +.BR write (2) > +or > +.BR sendmsg (2) > +, > +or call > +.BR write (2) > +or > +.BR sendmsg (2) > +with > +.B MSG_FASTOPEN > +flag directly, > +instead of both on the same connection. > +.IP > +Here is the typical call flow with this new option: > +.IP > +.in +4n > +.EX > +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); > +.EE > +.in > +.IP > .SS Sockets API > TCP provides limited support for out-of-band data, > in the form of (a single byte of) urgent data. > -- > 2.33.0.685.g46640cef36-goog >
