closedir - change in the libc

[Pawel Jakub Dawidek]

On Fri, Aug 09, 2013 at 12:59:34PM +0200, Jilles Tjoelker wrote:
> On Fri, Aug 09, 2013 at 11:59:48AM +0200, Mario Oshogbo wrote:
> > I'm a student attending in GSoC'13 in project "Write new features for
> > Capsicum" [1] and I would like to propose a little change to the libc.
> 
> > In the libc we have the function opendir(3) and fdopendir(3) which are
> > responsible for opening directories. We also have function closedir(3)
> > which is responsible for free the structure allocated by two previous
> > funcions.
> 
> > The problem with the closedir(3) is that he close fd used as argument of
> > fdopendir(3). I think programmer should be able to make a choice if he
> > want to close this descriptor automatically or not. Of course we are
> > able to use for dup(2) function and save fd before calling fdopendir(3)
> > to prevent closing but I think this is the one syscall which we could save.
> 
> > To support the propose I would like to give some example. I working now
> > on making the fts(3) more sandbox friendly which means I would like to
> > remove all fchdir(2) functions and operate only on fd. One of the steps
> > I perform is changing the opendir(3) to the fdopendir(3). I also must
> > remember the fd of currently opened directory after perform fclosedir.
> > If we have N of directories we must perform N additional dup(2) and N
> > additional close(2) functions to save this fd.
> 
> > So I would like to propose function called fdclosedir which will free
> > DIR structure but will not close fd attached to DIR structure. This
> > function also could return this fd which make it useful with the
> > opendir(3) function, when we don't know the fd but we would like free
> > DIR structure and perform some operations only on fd. I attach diff file
> > with my proposal of change.
> 
> While this looks sensible, the only advantage is cleaner code and less
> memory usage. Instead of additional dup()/close(), you could also keep
> the DIR around as long as you need the fd. [...]

This change is useful, I needed it in unrelated work to Mariusz's.
I wanted to "borrow" my directory descriptor to some function, which
were doing fdopendir(3) on it and to make it possible to not leak memory
on return from this function I had to dup(2) this descriptor.

I'd love to see fdclose() for similar reasons (see bin/75767, among
others).

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://mobter.com
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