[CC+= Andi, this time with the right address] On Fri, Nov 21, 2008 at 11:06 AM, Michael Kerrisk <mtk.manpages@xxxxxxxxxxxxxx> wrote: > Hello Stephen, > > Back in 2.6.13, you added the TCP_CONGESTION sockopt, but > provided no man-page patch... > > Below is my attempt to document this sockopt. Could you please > review. Please don't assume I've well understood the code: I > may well have messed up in my reading of it, so review what > I've written with care. > > Also, a question: was the silent truncation of the returned > string on getsockopt() if optlen is too small really intended? > Would it not be/have been better to error on this case? > > Cheers, > > Michael > > > TCP_CONGESTION (since Linux 2.6.13) > Get or set the congestion-control algorithm for this > socket. The optval argument is a pointer to a > character-string buffer. > > For getsockopt() *optlen specifies the amount of space > available in the buffer pointed to by optval, which > should be at least 16 bytes (defined by the kernel- > internal constant TCP_CA_NAME_MAX). On return, the > buffer pointed to by optval is set to a null-terminated > string containing the name of the congestion-control > algorithm for this socket, and *optlen is set to the > minimum of its original value and TCP_CA_NAME_MAX. If > the value passed in *optlen is too small, then the > string returned in *optval is silently truncated, and no > terminating null byte is added. If an empty string is > returned, then the socket is using the default conges- > tion-control algorithm, determined as described under > tcp_congestion_control above. > > For setsockopt() optlen specifies the length of the con- > gestion-control algorithm name contained in the buffer > pointed to by optval; this length need not include any > terminating null byte. The algorithm "reno" is always > permitted; other algorithms may be available, depending > on kernel configuration. Possible errors from setsock- > opt() include: algorithm not found/available (ENOENT); > setting this algorithm requires the CAP_NET_ADMIN capa- > bility (EPERM); and failure getting kernel module > (EBUSY). > > --- tcp.7 2008-11-21 10:54:08.000000000 -0500 > +++ tcp.7.TCP_CONGESTION.patch 2008-11-21 10:53:36.000000000 -0500 > @@ -733,7 +733,58 @@ > socket options are valid on TCP sockets. > For more information see > .BR ip (7). > -.\" FIXME Document TCP_CONGESTION (new in 2.6.13) > +.TP > +.BR TCP_CONGESTION " (since Linux 2.6.13)" > +Get or set the congestion-control algorithm for this socket. > +The > +.I optval > +argument is a pointer to a character-string buffer. > + > +For > +.BR getsockopt () > +.I *optlen > +specifies the amount of space available in the buffer pointed to by > +.IR optval , > +which should be at least 16 bytes (defined by the kernel-internal constant > +.BR TCP_CA_NAME_MAX ). > +On return, the buffer pointed to by > +.I optval > +is set to a null-terminated string containing the name of the > +congestion-control algorithm for this socket, and > +.I *optlen > +is set to the minimum of its original value and > +.BR TCP_CA_NAME_MAX . > +If the value passed in > +.I *optlen > +is too small, then the string returned in > +.I *optval > +is silently truncated, and no terminating null byte is added. > +If an empty string is returned, then the socket is using the default > +congestion-control algorithm, determined as described under > +.I tcp_congestion_control > +above. > + > +For > +.BR setsockopt () > +.I optlen > +specifies the length of the congestion-control algorithm name > +contained in the buffer pointed to by > +.IR optval ; > +this length need not include any terminating null byte. > +The algorithm "reno" is always permitted; > +other algorithms may be available, depending on kernel configuration. > +Possible errors from > +.BR setsockopt () > +include: > +algorithm not found/available > +.RB ( ENOENT ); > +setting this algorithm requires the > +.B CAP_NET_ADMIN > +capability > +.RB ( EPERM ); > +and failure getting kernel module > +.RB ( EBUSY ). > +.I > .TP > .B TCP_CORK > If set, don't send out partial frames. > > > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
