Re: [9fans] Re: some Plan9 related ideas

[Uriel <uriell@binarydream.org>]

On Mon, Oct 17, 2005 at 09:03:22AM -0400, Russ Cox wrote:
> I redefined use of the same tag to mean "you have to finish the
> previous message with this tag before processing this message",
> so that if you send a Topen followed by a Tread and the open
> blocks for whatever reason (disk i/o, say), the remote server
> doesn't try to run the Tread and send back a "fid not in use"
> error or some such.
Yes, that would be a problem with threaded servers, as you indicated.
 
> > Could you explain with more detail how it would work from the (threaded)
> > server POV? I was thinking that the server could use the fid to avoid
> > threads stepping into each other, and still avoid having to change the
> > protocol at all...
> 
> The threaded server would just have a list of requests associated with
> each tag instead of a single request.  When it finishes one it can move
> on to the next.
> 
> Under the current protocol you are not allowed to send a Tread request
> using a fid that the server has not acknowleged via Rattach or Ropen.
Ah! I was not aware of this restriction.

> So your approach still requires redefining the protocol.  Also I might have
> multiple I/Os going on and not care what order they get handled.
> Synchronization based on the fid changes current situations.  Basing it
> on the tag uses what were previously illegal situations.
Good point. I understand better now the reasons for your approach.
 
> > And I'm still curious what kernel changes nemo was talking about.
> 
> Read his post where he talks about mount -U.
> 
> If you mean readf and writef, those weren't kernel changes.
> They were the obvious library wrappers.
Sorry, I was not clear enough, I was referring to this:

"We added two (library) calls readf and writef that perform file I/O
besides resolving the name. We found ourselves calling them a lot, because
in many cases it's very convenient. They would be
an opportunity to "batch" walk/open/read(s)/clunk, which happen
a lot. However, this would require changing the kernel (even more than we
did for Plan B)."

(BTW, I get the feeling that readf/writef might be convenient, but you could
easily end up sending superfluous walks/opens/clunks) 

And I'm not convinced by Plan B's style of 'one value per file' for (almost?)
everything, maybe it smells to me too much of linux's sysfs :)

(Nothing wrong with 'one value per file' where it makes sense, I just don't
think it works well as a general rule)

uriel