David Laight <David.Laight@xxxxxxxxxx> wrote: > > > However, this might well cause a malfunction in UDP, for example. > > > MSG_MORE corks the current packet, so if I ask sendfile() say shove 32K > > > into a packet, if, say, 16K is read from the source and entirely > > > transcribed into the packet, > > > > If you use splice() for UDP, I don't think you would normally expect > > to get all that well-defined packet boundaries. > > Especially since (assuming I've understood other bits of this thread) > the splice() can get split into multiple sendmsg() calls for other > reasons. Yes - with SPLICE_F_MORE/MSG_MORE set on all but the last piece. The issue is what happens if the input side gets a premature EOF after we've passed a chunk with MSG_MORE set when the caller didn't indicate SPLICE_F_MORE? > What semantics are you trying to implement for AF_TLS? As I understand it, deasserting MSG_MORE causes a record boundary to be interposed on TLS. > MSG_MORE has different effects on different protocols. Do you mean "different protocols" in relation to TLS specifically? Software vs device vs device-specific like Chelsio-TLS? > For UDP the next data is appended to the datagram being built. > (This is really pretty pointless, doing it in the caller will be faster!) Splice with SPLICE_F_MORE seems to work the same as sendmsg with MSG_MORE here. You get an error if you try to append with splice or sendmsg more than a single packet will hold. > For TCP it stops the pending data being sent immediately. > And more data is appended. > I'm pretty sure it gets sent on timeout. Yeah - corking is used by some network filesystem protocols, presumably to better place RPC messages into TCP packets. > For SCTP the data chunk created for the sendmsg() isn't sent immediately. > Any more sendmsg(MSG_MORE) get queued until a full ethernet packet > is buffered. > The pending data is sent on timeout. > This is pretty much the only way to get two (or more) DATA chunks > into an ethernet frame when Nagle is disabled. SCTP doesn't support sendpage, so that's not an issue. > But I get the impression AF_TLS is deciding not to encode/send > the data because 'there isn't enough'. > That seems wrong. > > Note that you can't use a zero length sendmsg() to flush pending > data - if there is no pending data some protocols will send a > zero length data message. > A socket option/ioctl (eg UNCORK) could be (ab)used to force > queued data be sent. Yeah - I've changed that, see v4. I've implemented Linus's ->splice_eof() idea. David
