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Re: Bug#572733: support for mounting other kernel filesystems

On Mar 06, Petter Reinholdtsen <pere@hungry.com> wrote:

> > - cgroups (needed for accounting and management of system resources)
> I thought the libcgroup package handled this one, but might be wrong.
I understand that the cgconfig program from cgroup-bin does mount it
(in /mnt/cgroups/cpu, which I believe to be totally broken since /mnt
is not supposed to have subdirectories), but I do not think everybody
needs or wants to use cgconfig.

> In my opinion initscripts should limit itself to mount special file
> system that should be available on all or almost all installations and
> that do not introduce a security problem when mounted, and leave it to
> other packages to handle mounting of less common file system types.
Write access to cgroups and hugetlbfs is restricted to root by default.

> The request for mounting debugfs by default has so far been denied, as
> it have a rather special use case and can be seen as a security
> problem.
debugfs also already has a /sys/kernel/debug/ so it can easily be dealt
with in fstab. Since AFAIK it is not used by regular programs I see no
harm in having to configure it manually.

> For file system that should be mounted on Linux, depending on udev
> mith be ok, but for file systems that also should be mounted on
> kFreeBSD, I am told udev do not work and using udev is not an option.
> I suspect cgroups and hugetlbfs are linux specific, but wanted to
> mention the issue to be sure it is known.
Obviously these are Linux-specific filesystems. The porters to other
kernels will deal with their own system-specific filesystems...

> On Linux, using udev is supposed to be optional, but it is getter
> harder and harder to to avoid it, so I am not sure we want to spend
> extra effort to make it easier to drop udev from an installation.
udev is not intended to be optional, even if some systems currently work
well enough without udev nobody should rely on this to be true in the
future as well.

> I have no opinion on the mount point location, but would like all
> distributions to agree on the same location to make it easier for
> users and application writers to move applications from OS to OS.
Good luck. Obviously this will not happen in time for squeeze, so we
need a solution anyway.
The cgroups upstream maintainers stated that they are not interested in
mandating any specific location.

> > The upstream developers do not take a position either, but
> > /dev/cgroup/ and /dev/cgroups/ are popular choices.
> What are the other choices?  What do Ubuntu, SuSe, Mandriva, Gentoo
> and the other distributions do?  Which mount point is most commonly
> used?
I do not think other distributions have infrastructure to mount this
filesystem except for what is provided by cgconfig.
The upstream developers stated that they do not want to recommend any
specific directory, I think the only common alternative I have seen is

> Do not know.  For me it depend on how many installations should have
> these file systems mounted.  If it is all or almost all -> init.d
> scripts in the initscripts package and if it is some instalations ->
> sysadmin can add it himself or separate pacage.
The sysadmin currently CANNOT mount these filesystems by itself below
/dev because there is no mount point at boot time.
This may be the best solution, but it still needs some work in a
standard package.

On Mar 06, Mike Hommey <mh@glandium.org> wrote:

> /dev/something just feels so wrong. /dev contains block and character
> devices, and almost nothing else (except some udev and initramfs files)
> Why should cgroups control files, which are hardly device files, be
> found under /dev ?
Why not? /dev/pts/ is a kernel filesystem mounted below /dev, and /dev
itself is a kernel filesystem (tmpfs or devtmpfs).
And /dev will still be much less controversial than mount points in / .


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