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Re: Research using L4Hurd

From: Neal H. Walfield
Subject: Re: Research using L4Hurd
Date: 04 Jul 2002 14:32:53 +0200
User-agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/21.2

> I may well be confused, but I don't think I'm confused in that
> particular way. I was thinking about the server side of the
> i/o-interfaces. My impression is that most Hurd file servers call
> fshelp_manage_multithread which starts a new thread for each open.

After each open, the port is added to a port bucket which is managed
by either ports_manage_port_operations_multithread or

> > I think you are confused about L4 ipc.  Although the ipc is
> > synchronous, rpc do not have to be.
> What's the difference between ipc and rpc here? In the hurd, it seems
> the terms are used interchangably, and there's currently no truly
> *remote* procedure calls. One proposed terminology is to say that
> "ipc" is the microkernel communications primitive, and "rpc" is a
> combination of one or more ipcs that correspond to one operation as
> defined in some foo.defs file.

Sure, there are generally two ipcs per rpc, the send and the receive

> > Which is to say, when the client sends an ipc to a server, it blocks
> > until either the supplied timeout is reach or the server does a
> > receive.
> When I said "unnatural", I was thinking of the restriction that each
> thread can have at most one outstanding ipc call, i.e. a call that is
> waiting for a server to receive it. Is that correct?

In Mach, Mach proxies and buffers the requests so that you do not have
to wait for the server to do a receive.

> To have several outstanding rcp calls (per the above definition), the
> rpc must consist of two separate ipc:s, representing call and return.
> My impression have been that one goal is that most Hurd rpc calls
> should correspond to a single L4 ipc (with some exceptions like
> io_select), but I don't know if that's possible/practical.

Most will correspond to two L4 ipcs just like they correspond to two
rpcs in Mach.

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