A shame this has to be done within the kernel. There was never much reason to implement TCP handling in ring zero.
And debugger ruins everything; If the other side sends something larger than the local receive buffer it will usually disconnect after a while. as it will sense no one on the other end.
All the things that debugger can "ruin" should just be parametric - increase buffer sizes / keep alive times when debugging.
Also, there are more options than "kernel" and "each process for themselves" - you could have a "network/TCP daemon". QNX successfully does that for disk drivers and file system drivers - and likely network too. So does Minix.
It's just that historically, unix/linux/NT don't.
If the "minimum" was 2 hours then e.g. MSDN wouldn't be recommending that it be configured to 5 minutes would it? https://docs.microsoft.com/en-us/previous-versions/windows/i...
> And debugger ruins everything; If the other side sends something larger than the local receive buffer it will usually disconnect after a while. as it will sense no one on the other end.
"Everything"? Well when data isn't being sent then the connection could live on as long as it's kept alive by the kernel, right? Whereas with a userland implementation even that possibility becomes difficult.
You seem really intent on making unfounded blanket claims to rebut my point... but I feel like there's some validity to the point I'm making? It's be more helpful to see if you can instead find parts of it that might have some truth to them.
> It's just that historically, unix/linux/NT don't.
Yeah, hence why this approach seems problematic...
You could put BitTorrent in the kernel. It makes about as much sense architecturally, but isn't too widely used.
For example, you can have a process that reads a few bytes from a TCP socket and then passes the socket to another process.
Unix tries to model all I/O, including networking, as operations on files. Realistically it is only possible to get this right if the kernel is involved.
Of course it is quite possible to come up with different models. But Unix seems to be uniquely powerful in its ability to create complex systems from lots of small processes.
The kernel being involved does not imply that all code has to be in the kernel. The FUSE file system interface is a well known way to run filesystem code as user processes. Likewise, there are ways to run device drivers in user space.
The disavantage is that the extra context switches cause performance loss. So this approach is use for protocols that are rarely used and do not warrent full kernel implementation.
[1] boo hiss; I wish the spec was simply to truncate overlong packets at the MTU, and indicate that with a flag; the peers could then figure out what to do when a packet arrived that was shorter than its original length. Handling it in-band would mean it was more likely to arrive. Instead we can fragmenting it, which is icky, because defragmentation sucks; or we can drop it and sending an out of band message to the sender, but that message may not make it (and often doesn't). TCP could very easily adapt to 'i sent 1480 bytes of payload, but my peer is only acking 1472 each time, maybe I should send 1472 --- much easier and quicker than I keep sending packets and they don't get acked, maybe i should try sending smaller packets 15 seconds later.
Handle socket and port allocation, and then forward all packets to the relevant process unchanged.
The application software is then responsible for reconstructing packets into a reliable stream.
(This is partly a joke and partly a description of what actually happens with TOE "TCP Offload Engine" network cards.)