[Nix-dev] The fsync issues with nix

[Lluís Batlle i Rossell]

On Wed, Mar 21, 2012 at 08:58:43PM +0100, Lluís Batlle i Rossell wrote:
> On Wed, Mar 21, 2012 at 08:39:20PM +0100, Lluís Batlle i Rossell wrote:
> > On Wed, Mar 21, 2012 at 08:21:46PM +0100, Marc Weber wrote:
> > > You're asking to do fsync before registering store paths valid,
> > > correct?
> > > 
> > > If its not done yet it makes much sense to me.
> > 
> > Well, I think there are only two available operations: fsync(int fd) and sync().
> > One is much faster and less intrusive than the other. But what to do, when it
> > isn't nix that writes the files, and thus, nix has not the handles open?
> > Maybe sync() is the quick solution? Or should nix open all files and fsync them?
> 
> Just as an additional note, and as 'cwillu' pointed at #btrfs, 'mv' is an atomic
> operation for file entries, but not about the file contents. Only succesful
> fsync/sync will ensure the changes go to the hardcopy of the fs.
> 
> Additionally, I don't know if fsync() can be used effectively on a file already
> written and closed, by reopening it again. By the manpage I understand that it's
> possible to do that. But then I don't know why I can't find any user tool that
> fsyncs files.

Gaaaa in another computer where I put 'xfs', I'm getting zero-length files too.
I'm on X, run "nixos-rebuild switch --fast", and during the profile switch it
crashes, and the video screen goes mad.

Quite bad...