Re: [Xenomai] [pull] forge: Adjust default registry mount point

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Fri, Nov 28, 2014 at 10:55:56AM +0100, Jan Kiszka wrote:
> On 2014-11-28 10:50, Gilles Chanteperdrix wrote:
> > On Fri, Nov 28, 2014 at 10:40:27AM +0100, Jan Kiszka wrote:
> >> On 2014-11-28 00:15, Gilles Chanteperdrix wrote:
> >>> On Thu, Nov 27, 2014 at 09:43:34PM +0100, Jan Kiszka wrote:
> >>>> On 2014-11-27 21:34, Gilles Chanteperdrix wrote:
> >>>>> On Thu, Nov 27, 2014 at 02:14:38PM -0500, Lennart Sorensen wrote:
> >>>>>> On Thu, Nov 27, 2014 at 07:51:27PM +0100, Jan Kiszka wrote:
> >>>>>>> On 2014-11-27 19:18, Gilles Chanteperdrix wrote:
> >>>>>>>> According to the filesystem hierarchy standard, /mnt is the standard
> >>>>>>>> place for "temporarily mounted filesystems".
> >>>>>>>>
> >>>>>>>> http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
> >>>>>>>
> >>>>>>> Right, another reason to NOT mess around with it: if something was
> >>>>>>> temporarily mounted there, we will create the mountpoint inside that
> >>>>>>> filesystem with unforeseeable side effects.
> >>>>>>
> >>>>>> I always read that as "temporarily mounted there by the admin or some
> >>>>>> other human".  Certainly not automatic mounts by software.  There is a
> >>>>>> reason /media and such exists on many distributins.
> >>>>>
> >>>>> I would not venture an "always", autofs for instance, used to mount
> >>>>> things under /mnt. and /media has not always existed either, we used
> >>>>> /mnt/cdrom.
> >>>>
> >>>> FHS on /mnt purpose:
> >>>>
> >>>> "This directory is provided so that the system administrator may
> >>>> temporarily mount a filesystem as needed. The content of this directory
> >>>> is a local issue and should not affect the manner in which any program
> >>>> is run."
> >>>>
> >>>> I think this makes it crystal clear that Xenomai is not supposed to
> >>>> touch it.
> >>>
> >>> Just to add another argument. I just asked a friend who is a
> >>> professional sysadmin. He creates directory under /mnt and mount
> >>> things under these directories. So, I am not sure the standard is
> >>> even applied by the people who should use it.
> >>>
> >>> If you read on the last site I sent, under the /media article: 
> >>>
> >>> Amid much controversy and consternation on the part of system and
> >>> network administrators a directory containing mount points for
> >>> removable media has now been created. Funnily enough, it has been
> >>> named /media.
> >>>
> >>> Are you sure, 100% sure, that every Xenomai user expects to be able
> >>> to use /mnt as a mount point? Or that they will create directories
> >>> under /mnt like everybody has been doing since Linux exists?
> >>
> >> I'm both absolutely sure that a) has to be left alone by Xenomai because
> >> of requirements of the FHS and the way /mnt is used and b) we should try
> >> hard to avoid creating temporary dirs in persistent filesystems.
> > 
> > This is ridiculous. Because the standard changed, and one
> > distribution, Debian, decided to follow the new standard, which
> > seems to be not widely accepted, and even controversial, you want to
> > impose what Debian does to everybody. The distribution I use has
> > mount points under /mnt. So, why following Debian and not the
> > distribution I use, and what sysadmin have been doing for ages?
> > 
> > You want the mount point to be somewhere else? Fine, put a symbolic
> > link.
> > 
> > mkdir /run/xenomai
> > ln -s /run/xenomai /mnt/xenomai
> 
> Again, this is not acceptible as /mnt changes all the time and exposes
> various remote filesystems which will hide that link. /mnt is locally
> owned, not by the system to which Xenomai belongs, please accept this.
> You can still define your personal setup differently if the path is not
> easily fixable there.

In fact, the point is. Putting xenomai mount point under /mnt does
not even break Debian. Because of the new standard, there is little
chance for any Debian package to mount anything on /mnt or under
/mnt.

It is simply the local admin decision to decide to respect or not
respect the standard. I have been using Debian since 1997 (up to
back a few days, where I finally switched), and ALWAYS mounted
things in /mnt subdirectories. And never had any problems with any
Debian packages (and as I said, I seem to remember that some
versions of the autofs packages had their mount points under /mnt,
at any rate, the autofs mount points changed with debian versions,
so, if you had them in one place and upgrading, it would have been a
PIT to follow what Debian imposed).

The standard changes the usage of /mnt, but does not provide a
replacement. So, what we are left are choices among directories that
are not specifically made for mounting things. I do not like that
option.

So yes, when using Xenomai, the user will have to accept to not
follow the standard and create a /mnt/tmp directory for temporary
mounts. But I suspect this is an issue nobody cares about, I mean,
except you and Lennart.

-- 
					    Gilles.