[CRIU] irmap: Can't stat /no-such-path: No such file or directory

[Tycho Andersen]

On Mon, Sep 07, 2015 at 11:37:09AM +0300, Pavel Emelyanov wrote:
> On 09/05/2015 06:17 AM, Tycho Andersen wrote:
> > Hi all,
> > 
> > With newer versions of ubuntu (host and guest), I'm seeing the error
> > listed in the subject. The full log is:
> 
> This path was put there deliberately to make sure irmap resolver
> doesn't break on non-existing paths :)

A ha :)

> > http://paste.ubuntu.com/12279228/
> > 
> > It seems to me like we shouldn't be trying to stat no-such-path, but
> > that seems like the symptom of a larger problem which is that we can't
> > otherwise resolve the handle.
> > 
> > I resolved the inode using debugfs, and it says it's /var/log in the
> > container, which is not one of our heuristic paths we check:
> > 
> > # debugfs -R 'ncheck 525799' /dev/vda1
> > debugfs 1.42.12 (29-Aug-2014)
> > Inode Pathname
> > 525799  /var/lib/lxd/containers/unpriv/rootfs/var/log
> > 
> > If I add this path (and several others, see the attached patch) to the
> > list of irmap hints, it works fine. Obviously this isn't sustainable
> > though; is there some nicer solution to this?
> 
> Well, right now we don't have any :( The problem here is that *notify
> objects are assigned on inode and kernel can drop all the path information
> from it. So once we meet an *notified inode we _try_ to ask kernel for
> path and, if it fails, have no other ways to resolve it back.

Hmm, ok. Can we not ask debugfs like I did above? Or is it possible
that debugfs would also not know?

I can see two potential solutions in that case: 1. we could just
hardcode these paths (as they're needed by systemd bits) or 2. we
could add a --irmap-path argument, to allow users to specify which
paths are interesting and need to be checked. I'm happy to send a
patch for whatever you think is appropriate.

Tycho

> > Thanks,
> > 
> > Tycho
> > 
> > 
> > 
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>