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Date: Mon, 14 Jan 2013 16:37:15 -0500
From: Ryan Johnson <ryan DOT johnson AT cs DOT utoronto DOT ca>
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Subject: Re: stat() and tilde prefix (was bad bash tab completion)
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On 14/01/2013 3:24 PM, Stephan Mueller wrote:
> Perhaps (as you may well have already considered):
>
> - replace the path prefix by the mount point first?  (this may be naïve
>    on my part, but it's not clear to me that .. early in a path should be able
>    to influence which mount point is substituted)
If I mount something at /foo/bar/baz, then /foo/bar/baz/../../blah 
definitely shouldn't end up inside baz.

> - test directory existence of the component preceding .. before collapsing
>    (in the example above) b/.. to nothing.
> - trust that for a/b3/b2/b/../../../c, the existence test of a/b3/b2/b
>    before collapsing b/.. to nothing implies existence of b2 and b3 so no
>    further tests are needed for 'runs' of .. components with enough
>    components before them
>
> Understood that this is still going to cause a slowdown because paths with
> .. are not uncommon, but it would reduce the number of additional
> existence checks from one-per-path-component to one-per-run-of-..,
> which means none in the case of paths without .. in them.
The rest seems totally reasonable to me, FWIW.

I wouldn't put it past a Makefile (esp. one generated by autotools) or a 
gcc header search path to generate paths like: 
/a/b/c/d/../e/../f/../../../g/h (which resolves to a/g/h, if I counted 
dots correctly). Even then, though, it's "only" three checks to achieve 
posix-compliant behavior.

Ryan


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