Apparently this can cause a major speedup on some iSCSI targets, which
will otherwise wait for a timer to expire before responding. It
doesn't seem to hurt other simple TCP test cases (e.g. HTTP
downloads).
Problem and solution identified by Shiva Shankar <802.11e@gmail.com>
When sending to a multicast address, it may be necessary to specify
the source address explicitly, since the multicast destination address
does not provide enough information to deduce the source address via
the miniroute table.
Allow the source address specified via the data-xfer metadata to be
passed down through the TCP/IP stack to the IPv4 layer, which can use
it as a default source address.
This brings us in to line with Linux definitions, and also simplifies
adding x86_64 support since both platforms have 2-byte shorts, 4-byte
ints and 8-byte long longs.
Maintain state for the advertised window length, and only ever increase
it (instead of calculating it afresh on each transmit). This avoids
triggering "treason uncloaked" messages on Linux peers.
Respond to zero-length TCP keepalives (i.e. empty data packets
transmitted outside the window). Even if the peer wouldn't otherwise
expect an ACK (because its packet consumed no sequence space), force an
ACK if it was outside the window.
We don't yet generate TCP keepalives. It could be done, but it's unclear
what benefit this would have. (Linux, for example, doesn't start sending
keepalives until the connection has been idle for two hours.)
request(), seek() or deliver_xxx() in order to start the data flow.
Autonomous generators must be genuinely autonomous (having their own
process), or otherwise arrange to be called. TCP does this by
starting the retry timer immediately.
Add some debugging statements.
tcpip_tx(). This avoids the irritating wait when you accidentally type
"kernel pxelinux.0" before bringing up the network interface.
Add ENETUNREACH to strerror()'s list.
"when SYN is ACKed and we have already received SYN", or
"when SYN is received and we have already had SYN ACKed"
rather than just
"when SYN is ACKed"
This avoids spuriously calling the connected() method when we receive
a RST,ACK in response to a SYN.
Truncate TX length to TCP window at time of transmission rather than at
time of adding to TX packet; this is conceptually cleaner and also allows
the application to call tcp_send() multiple times to build up a single
packet.
"flags that are currently being sent". This allows at least one special
case (checking that we haven't already sent a FIN in tcp_rx_fin()) to be
collapsed.
