Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!VAX.FTP.COM!jbvb
From: jbvb@VAX.FTP.COM (James Van Bokkelen)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: An attempt to rekindle interface discuissions...
Message-ID: <8803041656.AA03791@vax.ftp.com>
Date: 4 Mar 88 16:56:09 GMT
References: <8803040730.AA11717@trwind.ind.TRW.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 33

FTP Software's 2.0 asynch interface allows the following:

You can make any non-blocking kernel call (including writes and closes/aborts),
provided that you don't interrupt a blocked syscall of the same type from the
mainline program on the same network descriptor.  In other words, you can
net_write from an asynch handler while the mainline is blocked in net_read
on the same descriptor, and you can net_abort from the asynch handler, but
don't try another net_read.

We support two kinds of handlers.

1. User upcall written in assembly, that doesn't need to save registers, but
does have to switch stacks.

2. C-language upcall, where the stack switch is already done, but the stack
isn't awfully large (2400 bytes).

Interrupts are enabled at entry to either kind.  You aren't guaranteed to
be synchronized with either DOS or the mainline, so you have to do your own
check before you can use O/S services.  In general, our asynch handlers
aren't supposed to take *too* long, because you're locking out other asynch
upcalls, and the kernel won't preempt your handler to do packet processing.

Since our normal network descriptors are allocated from a particular program's
file descriptor space, and we can't associate a PID with a system call made
from an asynch handler, we require that all network descriptors used from
within asynch handlers be global (unique in the system).

I don't know what goals others have.  We have the sockets at source-code
level, and our native interrupt-based interface at binary level (you can
substitute any of our various TCP/IP kernels without changing your .EXE
file, if you need to change interfaces).

jbvb