Re: [PATCH] real_path: make real_path thread-safe

["Torsten Bögershausen" <tboegi@web.de>]

On Wed, Dec 07, 2016 at 02:13:35PM -0800, Brandon Williams wrote:
> On 12/07, Junio C Hamano wrote:
> > Torsten Bögershausen <tboegi@web.de> writes:
> > 
> > > But in any case it seems that e.g.
> > > //SEFVER/SHARE/DIR1/DIR2/..
> > > must be converted into
> > > //SEFVER/SHARE/DIR1
> > >
> > > and 
> > > \\SEFVER\SHARE\DIR1\DIR2\..
> > > must be converted into
> > > \\SEFVER\SHARE\DIR1
> > 
> > Additional questions that may be interesting are:
> > 
> >     //A/B/../C		is it //A/C?  is it an error?
Yes, at least under Windows.
If I have e.g. a Raspi with SAMBA, I can put a git Repository here: 

//raspi/torsten/projects/git
If I use
git push //raspi/torsten/../junio/projects/git
that should be an error.

> >     //A/B/../../C/D	is it //C/D?  is it an error?
> > 

Same for
git push /raspi/../raspi2/torsten//projects/git


> 
> 
> Also is //.. the same as //?  I would assume so since /.. is /
> 
Under Windows //.. is simply illegal, I would say.
The documentation here
https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

Mentions these 2 examples, what to feed into the WIN32 file API:

a)
\\?\D:\very-long-path

b)
\\server\share\path\file"

c)
"\\?\UNC\server\share\path" 

So whatever we do, the ".." resoltion is only allowed to look at 
"very-long-path" or "path".

Some conversion may be done in mingw.c:
https://github.com/github/git-msysgit/blob/master/compat/mingw.c
So what I understand, '/' in Git are already converted into '\' if needed ?

It seams that we may wnat a function get_start_of_path(uncpath),
which returns:

get_start_of_path_win("//?/D:/very-long-path")         "/very-long-path" 
get_start_of_path_win("//server/share/path/file")      "/path/file"
get_start_of_path_win("//?/UNC/server/share/path")     "/path"
(I don't know if we need the variant with '\', but is would'n hurt):
get_start_of_path_win("\\\\?\\D:\\very-long-path")         "\\very-long-path" 
get_start_of_path_win("\\\\server\\share\\path\\file")      "\\path\\file"
get_start_of_path_win("\\\\?\\UNC\\server\\share\\path")     "\\path"

Then the non-windows version could simply return
get_start_of_path_non_win(something)     something

Does this make sense ?