On Thu, Sep 22, 2011 at 06:15:53AM +0200, Michael Kerrisk wrote: > Ben, Neil, > > On Tue, Sep 20, 2011 at 4:31 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote: > > 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> > > Ben, thanks for writing this, and Neil, thanks for reviewing it. I've > applied that change for man-pages-3.34. > > Ben, I added one small piece ti the description of > /proc/sys/net/ipv4/ip_no_pmtu_disc. For completeness, I've reproduced > the entire text below. Perhaps you could take a quick scan, to make > sure that the changed text is consistent with the whole piece. > This looks good to me. A minor nit in the chunk you added thoguh. Calling the MTU discovery value 'flags' suggests they can be or-together, or somehow otherwise combined, which is non-sensical. It may be better to use the term values rather than flags. Other than that Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx> Thanks! 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
