Re: [GSoC][PATCH v7 06/10] dir-iterator: add flags parameter to dir_iterator_begin

[Matheus Tavares Bernardino <matheus.bernardino@usp.br>]

On Thu, Jun 27, 2019 at 3:47 PM Johannes Schindelin
<Johannes.Schindelin@gmx.de> wrote:
>
> Hi Matheus,
>
> On Thu, 27 Jun 2019, Matheus Tavares Bernardino wrote:
>
> > On Wed, Jun 26, 2019 at 3:04 PM Junio C Hamano <gitster@pobox.com> wrote:
> > >
> > > Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
> > >
> > > > Hi Matheus,
> > > >
> > > > On Tue, 18 Jun 2019, Matheus Tavares wrote:
> > > >
> > > >>[...]
> > > >> +/*
> > > >> + * Look for a recursive symlink at iter->base.path pointing to any directory on
> > > >> + * the previous stack levels. If it is found, return 1. If not, return 0.
> > > >> + */
> > > >> +static int find_recursive_symlinks(struct dir_iterator_int *iter)
> > > >> +{
> > > >> +    int i;
> > > >> +
> > > >> +    if (!(iter->flags & DIR_ITERATOR_FOLLOW_SYMLINKS) ||
> > > >> +        !S_ISDIR(iter->base.st.st_mode))
> > > >> +            return 0;
> > > >>
> > > >> +    for (i = 0; i < iter->levels_nr; ++i)
> > > >> +            if (iter->base.st.st_ino == iter->levels[i].ino)
> > > >
> > > > This does not work on Windows. [[ Windows port does not have
> > > > usable st_ino field ]]]
> > >
> > > And if you cross mountpoint, st_ino alone does not guarantee
> > > uniqueness; you'd need to combine it with st_dev, I would think,
> > > even on POSIX systems.
> >
> > Ok, thanks for letting me know. I'm trying to think of another
> > approach to test for recursive symlinks that does not rely on inode:
> > Given any symlink, we could get its real_path() and compare it with
> > the path of the directory current being iterated. If the first is a
> > prefix of the second, than we mark it as a recursive symlink.
> >
> > What do you think of this idea?
>
> I think this would be pretty expensive. Too expensive.

Hmm, yes unfortunately :(

> A better method might be to rely on st_ino/st_dev when we can, and just
> not bother looking for recursive symlinks when we cannot,

What if we fallback on the path prefix strategy when st_ino is not
available? I mean, if we don't look for recursive symlinks, they would
be iterated over and over until we get an ELOOP error. So I think
using real_path() should be less expensive in this case. (But just as
a fallback to st_ino, off course)

> like I did in
> https://github.com/git-for-windows/git/commit/979b00ccf44ec31cff4686e24adf27474923c33a

Nice! At dir-iterator.h the documentation says that recursive symlinks
will be ignored. If we don't implement any fallback, should we add
that this is not available on Windows, perhaps?

> Ciao,
> Johannes