Re: [PATCH v6 1/6] submodules: add helper functions to determine presence of submodules

[Brandon Williams <bmwill@google.com>]

On 12/02, Jacob Keller wrote:
> On Fri, Dec 2, 2016 at 10:36 AM, Brandon Williams <bmwill@google.com> wrote:
> > On 12/01, Jeff King wrote:
> >> On Thu, Dec 01, 2016 at 01:56:32PM -0800, Stefan Beller wrote:
> >>
> >> > > Bleh. Looks like it happens as part of the recently-added
> >> > > get_common_dir(). I'm not sure if that is ever relevant for submodules,
> >> > > but I guess in theory you could have a submodule clone that is part of a
> >> > > worktree?
> >> >
> >> > Sure we can, for a test that we don't have that, see the embedgitdirs series. ;)
> >> >
> >> > For now each submodule has its own complete git dir, but the vision
> >> > would be to have a common git dir for submodules in the common
> >> > superprojects git dir as well, such that objects are shared actually. :)
> >>
> >> Fair enough. Given that it seems to behave OK even in error cases, the
> >> simple stat() test may be the best option, then. I do think we should
> >> consider adding a few test cases to make sure it continues to behave in
> >> the error cases (just because we are relying partially on what git's
> >> setup code happens to do currently, and we'd want to protect ourselves
> >> against regressions).
> >
> > For the naive (ie me), is there a reason why real_path() couldn't be
> > re-implemented to avoid using chdir?  I tried looking into the history of
> > the function but couldn't find anything explaining why it was done that
> > way.  I assume it has to do with symlinks, but I thought there was a
> > syscall (readlink?) that could do the resolution.
> >
> > --
> > Brandon Williams
> 
> The reason as far as I understand it, is that it uses chdir() to
> guarantee that it follows symlinks correctly and then looks up the
> resulting path after the chdir(). I do not think there is a syscall
> that actually correctly works like real_path() does. You *could*
> re-write real_path() to do the symlink lookups itself, but as Jeff
> recently pointed out, that way lies madness.

So is there a reason why the library function realpath() can't be used?
From a cursory look at its man page it seems to do the symlink
resolution.

-- 
Brandon Williams