Subject: Re: [RFC] git checkout $tree -- $path always rewrites files

From: Jeff King <[email-masked]>
Date: Fri, 7 Nov 2014 14:15:55 -0500

On Fri, Nov 07, 2014 at 05:13:47PM +0700, Duy Nguyen wrote:

> > By the way, one other thing I wondered while looking at this code: when
> > we checkout a working tree file, we unlink the old one and write the new
> > one in-place. Is there a particular reason we do this versus writing to
> > a temporary file and renaming it into place?  That would give
> > simultaneous readers a more atomic view.
> >
> > I suspect the answer is something like: you cannot always do a rename,
> > because you might have a typechange, directory becoming a file, or vice
> > versa; so anyone relying on an atomic view during a checkout operation
> > is already Doing It Wrong.  Handling a content-change of an existing
> > path would complicate the code, so we do not bother.
> 
> Not a confirmation, but it looks like Linus did it just to make sure
> he had new permissions right, in e447947 (Be much more liberal about
> the file mode bits. - 2005-04-16).

Thanks for digging that up. I think that only gives us half the story,
though. That explains why we would unlink/open instead of relying on
just open(O_TRUNC). But I think opening a new tempfile would work the
same as the current code in that respect.

-Peff