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Fixed mounting with containerized kubelet #23435

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Apr 13, 2016
Merged

Fixed mounting with containerized kubelet #23435

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1 change: 1 addition & 0 deletions pkg/util/mount/mount.go
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@ type Interface interface {
// consistent.
List() ([]MountPoint, error)
// IsLikelyNotMountPoint determines if a directory is a mountpoint.
// It should return ErrNotExist when the directory does not exist.
IsLikelyNotMountPoint(file string) (bool, error)
}

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6 changes: 6 additions & 0 deletions pkg/util/mount/nsenter_mount.go
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Expand Up @@ -170,6 +170,12 @@ func (n *NsenterMounter) IsLikelyNotMountPoint(file string) (bool, error) {
return true, err
}

// Check the directory exists
if _, err = os.Stat(file); os.IsNotExist(err) {
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This is going to run in the container's mount namespace -- don't we need to do this check in the host's mount ns?

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Kubernetes runs with /var/lib/kubernetes mounted to the same directory in the container so it works.

If you look e.g. into AWS volume plugin, it just calls mkdir() there without any nsenter. https://github.com/kubernetes/kubernetes/blob/master/pkg/volume/aws_ebs/aws_util.go#L75

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Isn't it /var/lib/kubelet?

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Let's imagine we have a directory /var/lib/kubelet/test which is a mount point which contains directory foo. Now, I think that if we call IsLikelyNotMountPoint for it var/lib/kubelet/test/foo we'd get false for newer versions of findmnt (see comment in line 186). If that's the case (I haven't tested this) your change would introduce a semantic change as now we'd return true.

I'm not saying it's a bad change, but we should say it explicitly.

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yes, it's /var/lib/kubelet, sorry.

@fgrzadkowski, I don't understand your point. If var/lib/kubelet/test/foo exist, this patch does not change a thing. Only if it doesn't we return ErrNotExist to tell the caller to create the directory before mounting.

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I agree. The change only affects the situation when the directory does not exist. I just want to make sure we are clear about semantics.

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@fgrzadkowski Personally I think this change is correct, and that the semantics are clear. Prior to this patch it is ambiguous how the dir-doesn't-exist case is handled; this makes nsenter_mount.go consistent with mount.go and documents the semantics.

glog.V(5).Infof("findmnt: directory %s does not exist", file)
return true, err
}

args := []string{"--mount=/rootfs/proc/1/ns/mnt", "--", n.absHostPath("findmnt"), "-o", "target", "--noheadings", "--target", file}
glog.V(5).Infof("findmnt command: %v %v", nsenterPath, args)

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