On Tue, Sep 20, 2011 at 10:12:34AM -0400, Benjamin Poirier wrote: > On 11-09-20 09:38, Neil Horman wrote: > > On Tue, Sep 20, 2011 at 09:29:54AM -0400, Benjamin Poirier wrote: > > > On 11-09-20 08:14, Michael Kerrisk wrote: > > > > Hello Benjamin, Neil, > > > > > [snip] > > > > > > > > Could you describe the required change in terms of how the man page > > > > text should look--i.e., rewrite the passage as you think it should > > > > look? > > > > > > How about changing it to: > > > IP_MTU_DISCOVER (since Linux 2.2) > > > Set or receive the Path MTU Discovery setting for a socket. When > > > enabled, the don't-fragment flag is set on all outgoing packets. > > > Linux will perform Path MTU Discovery as defined in RFC 1191 on > > > SOCK_STREAM sockets. For non-SOCK_STREAM sockets, it is the > > > user's responsibility to packetize the data in MTU sized chunks > > > and to do the retransmits if necessary. The kernel will reject > > > (with EMSGSIZE) datagrams that are bigger than the known path > > > MTU. The system-wide default is controlled by the > > > /proc/sys/net/ipv4/ip_no_pmtu_disc file. > > > > > > Path MTU discovery flags Meaning > > > [...] > > > > > > There are some differences between _DO and _WANT that are glossed over > > > in this description, but I suppose there's only so much detail you can > > > put in... > > > > > > Thanks, > > > -Ben > > > > > Yeah, I think thats close, but its only the users responsibility to package > > datagrams in mtu sized chunks if they force the dont fragment bit on. If they > > go wtih the default, the stack will fragment a datagram is it sees fit according > > to the mtu of the path it traverses > > Exactly. To get into this level of detail, I think we have to mention > the option value, not just enabled/disabled. Let's try like this: > > IP_MTU_DISCOVER (since Linux 2.2) > Set or receive the Path MTU Discovery setting for a socket. When > enabled, Linux will perform Path MTU Discovery as defined in RFC > 1191 on SOCK_STREAM sockets. For non-SOCK_STREAM sockets, > IP_PMTUDISC_DO forces the don't-fragment flag to be set on all > outgoing packets. It is the user's responsibility to packetize > the data in MTU sized chunks and to do the retransmits if > necessary. The kernel will reject (with EMSGSIZE) datagrams > that are bigger than the known path MTU. IP_PMTUDISC_WANT will > fragment a datagram if needed according to the path MTU or will > set the don't-fragment flag otherwise. > > The system-wide default can be toggled between IP_PMTUDISC_WANT > and IP_PMTUDISC_DONT by writting to the > /proc/sys/net/ipv4/ip_no_pmtu_disc file. > Yes, that sounds good to me. Thanks for doing this! Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx> Neil -- 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
