initial suggestions re. compiler server (bug #6565)

["Frank Ch. Eigler" <fche at redhat dot com>]

Hi, Dave -

(Background: we're prototyping a compile server split of stap, to
allow a central network server to perform arbitrary script translation
and compilation for a machine without local debuginfo nor compiler.
It'll be useful later for unprivileged user-space probing too.  Some
prototype code is in bug #6565.)


Here are some suggestions about the prototype code.

* The code might as well get checked into git and be developed there;
  it does not need to be make-install'd or systemtap.spec'd until
  later.

* The scripts are not #! /bin/sh but rather technically #! /bin/bash.

* The wire protocol can probably do everything based on two
  unidirectional bits of communication: one client->server tar.gz
  file to encode the arguments, given tapsets, the script; and one
  server->client tar.gz file to encode the results (.ko/.c files,
  stdout, stderr).

* It should be testable now even without networks via dejagnu making
  two named pipes ("mknod p FOO.1; mknod p FOO.2") and then starting
  the server & client scripts with redirected stdout/stdin.

* The networking aspect of it need not go through xinetd.  If we can't
  find a suitable shell-script-invokable tool to create/attach-to
  listening sockets, then perhaps a few-liner perl script could do the
  job.  That same perl script can use avahi-publish-service to push
  the actual (random) listening port number into mdns, so that 65000
  number need not be hardcoded anywhere.  Clients would find the
  server by abstract type (not _http._tcp but something like
  _systemtap._tcp) and name, and particularly with some cleverly
  chosen TXT description that should identify the server's assigned
  cross-compilation target.

* The client is not using the right avahi search entry points AFAIK.
  The avahi-discovery gui can pick up the full address/txt bits, and
  those are what the client will need to choose its favorite server.
  There must be some other command-line tool for that.

- FChE