On Fri, 21 Nov 2008 11:06:19 -0500 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). The tcp(7) man page is related and seems out of date as well. At least on this sytem (Ubuntu 8.04).it seems to be stuck back in pre 2.6.12 timewarp (see tcp_bic, tcp_bic_low_window, ...) values that no longer exist. Should be updated as well. -- 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
