Danny Milosavljevic <dan...@scratchpost.org> skribis:
> However, I think the actual point is to have all the "update" actions be
> atomic. Because there's something in the Linux kernel config (only on GuixSD;
> works just fine on Ubuntu) which makes my laptop crashy (on the first larger
> disk write after standby wakeup) I have some experience with Guix
> non-atomicity and let me tell you it's not good. (Just the other day it broke
> the substitute cache - so I couldn't use substitutes at all anymore; I've
> since found and deleted the cache directory contents)
When you stumble upon issues like this, please report them to
bug-g...@gnu.org with as many details as possible.
In the case of substitutes, files under /var/guix/substitute/cache are
written atomically; in guix/scripts/substitute.scm, it looks like this:
(with-atomic-file-output file
(lambda (out)
(write (cache-entry cache-url narinfo) out)
and effectively it writes to a temporary file, which is then rename(2)d.
I’m adding an fsync(2) call in ‘with-atomic-file-output’, which was
missing until now.
Regardless, you were very unlucky to end up with a truncated file. ;-)
Anyway, if your “crashy” setup allows you to uncover other issues in
this area, please do report them!
> Therefore, while I wouldn't replace (or re-symlink) the entire /boot on guix
> reconfiguration (it might be on its own partition, too), it *may* be useful
> to use include files and put these there atomically, one file per version.
> I'm not sure whether grub supports something like "include *.inc" with
> wildcards but that would be an idea.
Under /boot, the only thing that GuixSD’s code controls is grub.cfg,
which is created atomically (see ‘install-grub’ in (gnu build install).)
The other files are installed by ‘grub-install’.
Thanks for your feedback,
Ludo’.
