Re: [gentoo-dev] rfc: converting /etc/mtab to a symlink

[Richard Yao]

On 10/14/2013 12:34 PM, William Hubbs wrote:
> On Mon, Oct 14, 2013 at 10:46:38AM -0400, Richard Yao wrote:
>> On 10/14/2013 10:11 AM, Rich Freeman wrote:
>>> On Mon, Oct 14, 2013 at 9:52 AM, Richard Yao <ryao@g.o> wrote:
>>>> The Linux kernel also supports far more architectures than we do. That does not mean that we must support them too.
>>>>
>>>> With that said, how does changing things benefit/affect users, especially non-systemd users?
>>>
>>> Better support for namespaces, for one.
>>>
>>> If this is actually going to actually break something, by all means
>>> speak up.  Otherwise this really comes across as the whole
>>> I-DONT-LIKE-CHANGE argument.  I get it.  By all means don't make your
>>> /etc/mtab a symlink, and if down the road something doesn't work as a
>>> result feel free to fork it unless you can convince somebody else to
>>> make it work.  So far the only concrete issues that have been raised
>>> seem minor - pertaining to NFS and PAM (both having solutions
>>> available).
>>>
>>> If this causes trouble for the FreeBSD folks I'm interested in what
>>> kinds of compromises can be reached.  I think a challenge is that
>>> Linux and FreeBSD seem to be very slowly diverging - for software that
>>> lives near the kernel/userspace boundary that could make things
>>> interesting.  There doesn't seem to be much desire to limit Linux
>>> distros to purely POSIX behavior.
>
> As I said earlier in the thread, the planned baselayout change will only
> affect Linux.
>
>> My main concern is that some of the configure flags being proposed could
>> make packages that worked on Gentoo FreeBSD stop working there. I am not
>> making changes, but I think that there should be some benefit and that
>> care should be taken not to break things for everyone else.
>
> Richard, the packages we are discussing (nilfs-utils and nfs-utils)
> are linux-specific, so there is nothing to worry about on the *bsd side
> for them.

That is good to hear. There were a few situations int he past where
changes were made for Gentoo Linux that broke Gentoo FreeBSD, so I
wanted to be certain that we were not going to have a repeat of that here.

>> That being said, mgorny said that this adds support for mount
>> namespaces, but I have yet to hear an explanation of what that actually
>> means. What are the use cases?
>
> There has been a lot written on this; you might want to google
> "per-process namespaces".

If this merits discussion on the list, then it should merit answers for
these questions:

1. What are mount namespaces? How do they integrate with the kernel?
2. What does systemd do with them? What does systemd's use of them
provide to users?

Saying to google "per-process namespaces" does not really answer that.
Per-process namespaces provide a means to isolate processes into
containers that they have their own pid numbers and can neither nor
interact with processes outside of the container via traditional IPC
mechanisms such as signals. It is similar to the concept of FreeBSD
jails. That does not tell me what a "mount namespace is" or why systemd
has anything to do with it.