bug#12494: 0 exit status even when chmod fails

[Georgiy Treyvus]

I was helping a newbie friend of mine try to get some games of his 
running. It quickly became apparent that the program didn't have execute 
permission. I thought a simple chmod 755 would do the job. Apparently 
not. We try again and check afterwards. Still won't execute. We do it 
again. We check the exit status. Executable? No. Exit status? 0.  
Compiled for Linux and not say Winblowse? Yes. What the bloody hell was 
going on here?

There were a few more vain tries. We tried following through on other 
crackpot ideas of mine to no avail. Then came ripping out all the hair 
on my head and other places best left to the imagination, waiting for it 
to regrow and doing it all over again.

Finally I had him show me the mount options of the relevant partitions. 
Many I recognized. Some I did not. I started researching those I did 
not. It turns out they had nothing to do with the problem at hand. But I 
did inadvertently find out what went wrong as a consolation prize. 
Apparently chmod doesn't work on vfat or ntfs. Ultimately it was 
understandable as the permission schemes are radically different and now 
that I thought about it that'd be quite a feat to be able to translate 
between them in any meaningful way.

Chmod doesn't work on vfat? Fair enough. But it shouldn't be returning a 
0 exit code for failure. Generally when chmod fails or can't do 
something it returns an non-zero exit code. I see no reason that there 
should be an exception just because it's incompatible with vfat. This 
can be very problematic in scripts that rely on knowing the success of 
the command/exit code. Please look into this.