linux-kernel - Re: extra slash in current path

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Message-ID: <20110623142706.GA13310@elliptictech.com>
Date:	Thu, 23 Jun 2011 10:27:06 -0400
From:	Nick Bowler <nbowler@...iptictech.com>
To:	yuyichao-mit <yuyichao@....edu>
Cc:	richard -rw- weinberger <richard.weinberger@...il.com>,
	Lars Täuber <taeuber@...w.de>,
	linux-kernel@...r.kernel.org, linux-c-programming@...r.kernel.org
Subject: Re: extra slash in current path

On 2011-06-23 10:11 -0400, yuyichao-mit wrote:
> On Thu, Jun 23, 2011 at 9:54 AM, richard -rw- weinberger
> > Is this really a kernel issue?
> > rw@...coon:~> cd //
> > rw@...coon://> pwd
> > //
> > rw@...coon://> ls -l /proc/self/cwd
> > lrwxrwxrwx 1 rw users 0 23. Jun 15:53 /proc/self/cwd -> /
> 
> well, that's true, but this is indeed the retrun value of get_current_dir_name.

glibc's get_current_dir_name will honour the PWD environment variable in some
cases, which is where the // actually comes from (i.e., it does not come
from the kernel).

This funny behaviour of cd is actually specified by POSIX (man 1p cd):

        8. The curpath value shall then be converted to canonical form
           as follows, considering each component from beginning to
           end, in sequence:
[...]
            c. An implementation may further simplify curpath by
               removing any trailing slash characters that are not also
               leading slashes, replacing multiple non-leading
               consecutive slashes with a single slash, and replacing
               three or more leading slashes with a single slash.  If,
               as a result of this canonicalization, the curpath
               variable is null, no further steps shall be taken.

        9. [...] The PWD environment variable shall be set to curpath.

Cheers,
-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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