Re: readlink(1) behavior

[Dmitry V. Levin]

On Thu, Sep 10, 2009 at 07:29:35PM +0200, Jim Meyering wrote:
> Eric Blake wrote:
> > I think there are some infelicities in the canonicalization options of 
> > readlink.
> >
> > readlink -fv file/    => correctly reports ENOTDIR
> > readlink -fv missing  => lists /path/to/missing
> > readlink -fv missing/ => complains that missing is not a dir
> > readlink -mv file/    => lists /path/to/file
> > readlink -mv missing/ => lists /path/to/missing
> >
> > I would like to see: 'readlink -fv missing/' list '/path/to/missing', on the
> > grounds that one could do 'mkdir missing' to bring the path into existence;
> > this matches the documentation that -f ignores a missing final element 
> > (nowhere
> > does it say the final element has to be a non-file).
> 
> Yes, that makes sense.

Yes, but there is a corner case:
I think that 'readlink -fv broken_symlink/' behavior should not change.

> > Also, I think that -m should either be changed to reject paths that cannot
> > possibly exist given the current state of the file system (that is, in the
> > above case, 'readlink -mv file/' should fail with ENOTDIR), or we should 
> > create
> > a new option (in bewteen -f and -m) with that property.  For an example of 
> > how
> > this mode might be useful:
> >
> > Suppose we want to test whether 'mkdir -p a/b && touch a/b/c' will succeed,
> > without creating directories if it won't.  'readlink -f a/b/c' is 
> > insufficient,
> > since a/b might not yet exist.  'readlink -m a/b/c' is insufficient,
> > because 'a' might be a regular file or a symlink to itself.
> >
> > Maybe such an option can be named -p/--possible.

A new option for this new mode looks more appropriate,
I'd like to see old -m behavior unchanged for backwards compatibility.


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