Re: [silly] loose, pack, and another thing?

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> One thing that scares me about a regular "ln" between the worktree and
> odb is that you are very susceptible to corrupting the repository by
> modifying the worktree file with regular tools. If they do a complete
> rewrite and atomic rename (or link) to put the new file in place, that
> is OK. But opening the file for appending, or general writing, is bad.

Very true.

> You can get some safety with the immutable attribute (which applies to
> the inode itself, and thus any path that hardlinks to it). But setting
> that usually requires being root. And it creates other irritations for
> normal use (you have to unset it before even removing the hardlink).

As a regular user, "chmod a-w" has the same characteristics (works
at the inode level) but without "cannot remove it" downside.  It
used to be sufficient in RCS and CVS days, though, as a signal that
you are only to look at it without touching it, to "chmod a-w" a
path that is checked out but not for modifying.  Some editors even
offer to do chmod u+w for you when saving, so if we want absolute
safety, it may not be enough.

> It would be nice if there was some portable copy-on-write abstraction we
> could rely on, but I don't think there is one.

;-)