Re: fatal: Could not get current working directory: Permission denied | affected 2.10,2.11,2.12, but not 1.9.5 |

From: "René Scharfe" <l.s.r@web.de>
To: Jeff King <peff@peff.net>
Cc: Stefan Beller <sbeller@google.com>,
	Zenobiusz Kunegunda <zenobiusz.kunegunda@interia.pl>,
	"git@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: fatal: Could not get current working directory: Permission denied | affected 2.10,2.11,2.12, but not 1.9.5 |
Date: Fri, 17 Mar 2017 23:50:09 +0100	[thread overview]
Message-ID: <d27d4fd1-8069-ec53-df3f-c3e176f83f16@web.de> (raw)
In-Reply-To: <20170317222902.isndsmzy43btxh4i@sigill.intra.peff.net>

Am 17.03.2017 um 23:29 schrieb Jeff King:
> On Fri, Mar 17, 2017 at 10:07:18PM +0100, René Scharfe wrote:
>
>>>   As  an extension to the POSIX.1-2001 standard, Linux (libc4, libc5,
>>> glibc) getcwd()
>>>   allocates the buffer dynamically using malloc(3) if buf is NULL.  In
>>> this case, the
>>>   allocated buffer has the length size unless size is zero, when buf
>>> is allocated as big
>>>   as necessary.  The caller should free(3) the returned buffer.
>>>
>>> This sounds specific to Linux (though I am reading Linux man pages,
>>> which claim this; Also it seems I might have misread it as it also states
>>> "The pathname is returned as the function result and via the
>>> argument buf, if present.").
>>
>> I'm only interested in FreeBSD for now, as that's the platform Zenobiusz
>> reported the issue on and I haven't been able to reproduce it, so this is
>> still a bit exploratory, but hopefully getting closer.  This extension is
>> used in the first version of pwd(1) in FreeBSD's repo, comitted 1994-05-26,
>> so it was supported there basically forever.
>>
>> The oldest version I found that's using the extention is NetBSD's pwd(1),
>> which was committed 1993-03-21 and carries a SCCS timestamp of 1991-02-20.
>> Visual Studio .NET 2003 supports it as well.
>
> My big question is what happens on other platforms when they see a NULL
> (but 0-sized) buffer. Any reasonable implementation would just return
> ERANGE and we'd fall back to the existing code. But we often have to deal with unreasonable ones.
>
> So do we need a "my OS understands getcwd(NULL)" build knob?

POSIX specifies the behavior in this case as unspecified.  An 
implementation could offer a different extension, and e.g. return a 
pointer to a static buffer.  So the answer would probably be "yes" if 
this was a patch meant for public consumption.  For now it's only 
compatible with BSDs, Windows, MacOSX, Linux. :)

René