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

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

[Pavel Emelyanov]

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@xmission.com>

Acked-by: Pavel Emelyanov <xemul@parallels.com>

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

[Serge E. Hallyn]

Quoting Pavel Emelyanov (xemul@parallels.com):
> 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@xmission.com>
> 
> Acked-by: Pavel Emelyanov <xemul@parallels.com>

These patches haven't made it into linux-next or Linus' tree.  (More
worrisome, is that the several online linux-kernel mail archives I've
checked seem to have most of this thread, but not Eric's original
patch.)  What path were they expected to go in by?

thanks,
-serge

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

[Eric W. Biederman]

"Serge E. Hallyn" <serge@hallyn.com> writes:

> Quoting Pavel Emelyanov (xemul@parallels.com):
>> 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@xmission.com>
>> 
>> Acked-by: Pavel Emelyanov <xemul@parallels.com>
>
> These patches haven't made it into linux-next or Linus' tree.  (More
> worrisome, is that the several online linux-kernel mail archives I've
> checked seem to have most of this thread, but not Eric's original
> patch.)  What path were they expected to go in by?

I was hoping Al Viro would pick it up in the vfs tree, or at least
review the patch.  With a backup possibility that Andrew Morton might.

Given that the merge window is likely to open in next couple of days
I plan to resubmit this after the merge window closes. 

I don't have a clue what happened to the archives that day but it does
look like there was a significant mail hiccup as the number of messages
archived are way down.

Eric