Linux's getdents gets /.. inode number from host system under LXC

I can't reproduce this on my raring laptop.

ubuntu@r2:~$ ls -lid / /..
2783189 drwxr-xr-x 22 root root 4096 Jan 2 15:58 /
2783189 drwxr-xr-x 22 root root 4096 Jan 2 15:58 /..

Nor can I reproduce it on a precise instance running 3.2.0-35-virtual #55-Ubuntu:

ubuntu@p1:~$ ls -lid / /..
139754 drwxr-xr-x 22 root root 4096 Jan 2 16:09 /
139754 drwxr-xr-x 22 root root 4096 Jan 2 16:09 /..

Ok, sorry, I see now. Yes i can reproduce this with getdents of course.

This has nothing to do with lxc lying, and yes if you need to work around this you'll need to use blockdev-backed rootfs for the containers.

The container is set up with the tasks pivot_root'd into the container's /, which in your case is a bind mount. Resolution of '..' respects the fact that the /var/lib/lxc/container/rootfs should be root, and returns itself. However, there is only one actual directory entry for /var/lib/lxc/container/rootfs in all the kernel, and it's '..' (d_parent) points to /var/lib/lxc/container. Lxc can't do anything about that. The kernel's flexible mounts, bind mounts, and mounts namespaces provide different *views* of the filesystems, don't change what is in the actual filesystems.

Hi Serge,

You need to compile the C code on
http://www.kernel.org/doc/man-pages/online/pages/man2/getdents.2.html
and run it to see this issue. It's "getdent" sys-call that sees different
numbers. Please confirm

On Wed, Jan 2, 2013 at 6:10 PM, Serge Hallyn <email address hidden>wrote:

> Nor can I reproduce it on a precise instance running 3.2.0-35-virtual
> #55-Ubuntu:
>
> ubuntu@p1:~$ ls -lid / /..
> 139754 drwxr-xr-x 22 root root 4096 Jan 2 16:09 /
> 139754 drwxr-xr-x 22 root root 4096 Jan 2 16:09 /..
>
>
> ** Changed in: lxc (Ubuntu)
> Importance: Undecided => Critical
>
> ** Changed in: lxc (Ubuntu)
> Importance: Critical => Medium
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1094019
>
> Title:
> Linux's getdents gets /.. inode number from host system under LXC
>
> Status in “lxc” package in Ubuntu:
> New
>
> Bug description:
> Calling getdents on "/" gets the host system's inode number for /..,
> which is different from /. unlike real (non lxc) systems.
> This causes flexlm to fail
>
> More info at http://foss-boss.blogspot.com/2012/12/LXC-lies-about
> -..-inode-number-making-flexlm-unhappy.html
>
> ProblemType: Bug
> DistroRelease: Ubuntu 12.04
> Package: lxc 0.7.5-3ubuntu65
> ProcVersionSignature: User Name 3.2.0-34.53-virtual 3.2.33
> Uname: Linux 3.2.0-34-virtual x86_64
> ApportVersion: 2.0.1-0ubuntu15
> Architecture: amd64
> Date: Thu Dec 27 13:13:46 2012
> Ec2AMI: ami-2737b74e
> Ec2AMIManifest: (unknown)
> Ec2AvailabilityZone: us-east-1d
> Ec2InstanceType: t1.micro
> Ec2Kernel: aki-825ea7eb
> Ec2Ramdisk: unavailable
> KernLog:
>
> MarkForUpload: True
> ProcEnviron:
> TERM=xterm
> LANG=en_US.UTF-8
> SHELL=/bin/bash
> SourcePackage: lxc
> UpgradeStatus: No upgrade log present (probably fresh install)
> lxcsyslog:
>
> modified.conffile..etc.lxc.lxc.conf: [modified]
> mtime.conffile..etc.lxc.lxc.conf: 2012-12-04T17:17:14.072195
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1094019/+subscriptions
>

Ok I see, will use block backed lxc then. Thanks

On Wed, Jan 2, 2013 at 6:32 PM, Serge Hallyn <email address hidden>wrote:

> Ok, sorry, I see now. Yes i can reproduce this with getdents of course.
>
> This has nothing to do with lxc lying, and yes if you need to work
> around this you'll need to use blockdev-backed rootfs for the
> containers.
>
> The container is set up with the tasks pivot_root'd into the container's
> /, which in your case is a bind mount. Resolution of '..' respects the
> fact that the /var/lib/lxc/container/rootfs should be root, and returns
> itself. However, there is only one actual directory entry for
> /var/lib/lxc/container/rootfs in all the kernel, and it's '..'
> (d_parent) points to /var/lib/lxc/container. Lxc can't do anything
> about that. The kernel's flexible mounts, bind mounts, and mounts
> namespaces provide different *views* of the filesystems, don't change
> what is in the actual filesystems.
>
> ** Changed in: lxc (Ubuntu)
> Status: New => Won't Fix
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1094019
>
> Title:
> Linux's getdents gets /.. inode number from host system under LXC
>
> Status in “lxc” package in Ubuntu:
> Won't Fix
>
> Bug description:
> Calling getdents on "/" gets the host system's inode number for /..,
> which is different from /. unlike real (non lxc) systems.
> This causes flexlm to fail
>
> More info at http://foss-boss.blogspot.com/2012/12/LXC-lies-about
> -..-inode-number-making-flexlm-unhappy.html
>
> ProblemType: Bug
> DistroRelease: Ubuntu 12.04
> Package: lxc 0.7.5-3ubuntu65
> ProcVersionSignature: User Name 3.2.0-34.53-virtual 3.2.33
> Uname: Linux 3.2.0-34-virtual x86_64
> ApportVersion: 2.0.1-0ubuntu15
> Architecture: amd64
> Date: Thu Dec 27 13:13:46 2012
> Ec2AMI: ami-2737b74e
> Ec2AMIManifest: (unknown)
> Ec2AvailabilityZone: us-east-1d
> Ec2InstanceType: t1.micro
> Ec2Kernel: aki-825ea7eb
> Ec2Ramdisk: unavailable
> KernLog:
>
> MarkForUpload: True
> ProcEnviron:
> TERM=xterm
> LANG=en_US.UTF-8
> SHELL=/bin/bash
> SourcePackage: lxc
> UpgradeStatus: No upgrade log present (probably fresh install)
> lxcsyslog:
>
> modified.conffile..etc.lxc.lxc.conf: [modified]
> mtime.conffile..etc.lxc.lxc.conf: 2012-12-04T17:17:14.072195
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1094019/+subscriptions
>