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Date: Tue, 3 May 2005 15:22:58 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: mkdir -p and network drives
Message-ID: <20050503132258.GB27360@calimero.vinschen.de>
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References: <3 DOT 0 DOT 5 DOT 32 DOT 20050502232204 DOT 00b52180 AT incoming DOT verizon DOT net> <42777719 DOT 8090103 AT byu DOT net>
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On May  3 07:05, Eric Blake wrote:
>  rather than starting at the left and
> making sure each path component exists, the algorithm could start at the
> right and successively prune each rightmost component until it no longer
> gets ENOENT (or gets to the empty string), then build back up from that
> point.  Then, even though //MACHINE does not resolve to a directory,
> `mkdir -p //MACHINE/Share/existing/nonexisting' only has to check whether
> //MACHINE/Share/existing exists, and create nonexisting from there, rather
> than starting all the way from the problematic /, //, or //MACHINE.  The
> only drawback to this approach is that it would then require up to n
> stat() calls to decide where to start making directories, each processing
> O(n) names, which is the exact O(n^2) syscall overhead that the code was
> optimized to try to avoid by starting blindly at the leftmost component.

O(n^2)?  I see only O(n), regardless where the algorithm begins the search.
In any path of length n, you have a constant sum of n stat and mkdir calls,
AFAICS.

> The only other approach I can think of is to special case leading // (at
> least on cygwin, leading // should start after //MACHINE/Share/), but not
> all POSIX-compliant hosts have the same semantics for leading //, so I
> don't know how well such a special case would fold into upstream coreutils.

If coreutils is trying to be POSIX compliant, it has to allow and evalute
correctly two leading slashes:

http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap04.html#tag_04_11

Quote:

"A pathname that begins with two successive slashes may be interpreted in an
 implementation-defined manner, although more than two leading slashes shall
 be treated as a single slash."


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

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