Re: [PATCH] git-init: don't base core.filemode on the ability to chmod.

From: Junio C Hamano <gitster@pobox.com>
Date: Oct 4, 2007, 06:23 UTC
Message-ID: <7vr6kbbdph.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <470482A2.3080907@op5.se>

Andreas Ericsson <ae@op5.se> writes:

Show 15 quoted lines

> Johannes Schindelin wrote:
>> Hi,
>>
>> On Thu, 4 Oct 2007, Martin Waitz wrote:
>>
>>> -		filemode = (!chmod(path, st1.st_mode ^ S_IXUSR) &&
>>> +		/* test that new files are not created with X bit */
>>> +		filemode = !(st1.st_mode & S_IXUSR);
>>> +		/* test that we can modify the X bit */
>>> +		filemode &= (!chmod(path, st1.st_mode ^ S_IXUSR) &&
>>
>> Should that not be &&=?
>>
>
> I should think |=

Is it?

The issue that started the thread was that chmod + stat check we originally had would say executable bit "seems to be" kept, while that is only true until the information is cached at VFS layer.

We create config file without asking for executable bit, so if we read it back as executable then that is a sure sign that the filesystem does not know what it is talking about, and we set filemode to zero in such a case. Similarly, if the chmod + stat check says we cannot set executable bit and read it back, then we also know the filesystem does not know about filemode.

So I think we can write it like this (indentation aside)...

filemode = !( (st1.st_mode & S_IXUSR)
        	/* we did not ask for x-bit -- bogus FS */
	    || chmod(path, st1.st_mode & S_IXUSR)
        	/* it does not let us flip x-bit -- bogus FS */
	    || lstat(path, &st2)
        	/* it does not let us read back -- bogus FS */
	    || (st1.st_mode == st2.st_mode)
	        /* it forgets we flipped -- bogus FS */
	    );