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Date: Fri, 30 Jan 2015 15:19:35 -0500
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From: "Joel C. Salomon" <joelcsalomon@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] wstat and atomic directory change
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On Fri, Jan 30, 2015 at 10:59 AM, Giacomo Tesio <giacomo@tesio.it> wrote:
> As far as I can read intro(5), it explicitly excludes slash as a valid
> character for the Plan 9 OS, but it also explicitly states that "the
> protocol has no such restriction".

My reading is that a 9p2000 server might allow a filename of the form
"b/c"; e.g. this tree is possible:

    a
    |-- b
    |   +-- c
    |       +-- d
    +-- b/c
        +-- d

Note that "a" / "b" / "c" / "d" is distinct from "a" / "b/c" / "d".
Plan 9, because of its Unix heritage, will not be able to deal with
this, but the protocol has no such limitation. On the other hand, if
you bypass the OS and issue a Walk to "a/b/c/d", there is a
well-defined response required in the protocol -- either open the file
with that (impossible) name, or fail.

> Still, using this protocol "feature" to enable atomic directory change could
> be useful in my use cases, but I don't want to build yet another 9p2000
> extension.

It'll have to be an extension -- a technically incompatible one,
though the incompatibilities will not ever happen.

--Joel