Re: [PATCH] vfs: Add setns support for the mount namespace

From: Pavel Emelyanov
Date: Sat May 12 2012 - 07:42:52 EST

On 05/12/2012 12:54 AM, Eric W. Biederman wrote:
> setns support for the mount namespace is a little tricky as an arbitrary
> decision must be made about what to set fs->root and fs->pwd to, as
> there is no expectation of a relationship between the two mount
> namespaces. Therefore I arbitrarily find the root mount point, and
> follow every mount on top of it to find the top of the mount stack.
> Then I set fs->root and fs->pwd to that location. The topmost root of
> the mount stack seems like a reasonable place to be.
> Bind mount support for the mount namespace inodes has the possibility of
> creating circular dependencies between mount namespaces. Circular
> dependencies can result in loops that prevent mount namespaces from
> every being freed. I avoid creating those circular dependencies by
> adding a sequence number to the mount namespace and require all bind
> mounts be of a younger mount namespace into an older mount namespace.
> Add a helper function proc_ns_inode so it is possible to detect when we
> are attempting to bind mound a namespace inode.
> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>

Acked-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
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