Re: gmc/libvfs suggestion for removable media

[Daniel Burrows <Daniel_Burrows brown edu>]

On Tue, Feb 23, 1999 at 12:43:05PM -0500, Gleef was heard to say:
> 
> I mostly agree, the handling of removable media is outside the scope of
> GNOME, particularly since the issue is already well handled outside of
> GNOME.  For people who want easy automounting of removable media, Linux
> offers AutoFS, and for other platforms (and Linux) there is AMD.  For
> people who want careful control over what gets mounted, they can refrain
> from using either system, and use the standard mount command.

  I had a different message typed but I stopped to do a field test of how
well Linux handles removable media, and got a hard kernel lock.  This
might be my system, though..it survived reading from a non-existant disk
("read error") and writing to a non-existant disk ("no space on device" or
"read-only filesystem" errors)  But then when I put the disk back in,
umounted/remounted it, and copied a file to it everything went boom (my
syslog shows a filesystem panic).  I'll try copying to a floppy without the
extra fooling around in a sec but I want to type this and send it first. :-)
(I don't use floppies much since I have an ethernet connection at the moment,
but I did in the past and it's a major pain in Linux.  And I'm someone who's
at peace with mount/umount. My mother has trouble copying to drive A: when
it has a picture of a floppy next to it..I don't want to imagine her trying
to mount and unmount drives, no matter how pretty the interface.  And don't
tell me on GNOME-list that my mother shouldn't use Unix.  I'm here because
I want her to be able to.)

  I may look into AutoFS and see how much of what I was thinking of it
implements.  But I don't care that much about automounting--I'm aware there
are tools for that--or about synchronous transfer--I'm also aware of how
to mount -o sync--but the problem is that the kernel seems to get confused
if I take a disk out while it has a logically mounted filesystem--or worse,
change disks. (cdroms seem to give a media changed message but I don't know
about other devices.  Hmm--syslog shows that the last message before everything
want black was "busy inodes on changed media.")  Aside from reworking the
semantics of mount/umount, the only really feasible thing to do (IMO) is to
wrap writes to transient devices in a safe manner.  Also, it should be
possible for a program which tries to access a nonavailable drive to ask
the user to please put the disk back in.  AFAIK, no automounting/kernel-based
facility can do that.  gmc at least has to deal with that.

> 
> The extent of mc's involvment id such issues should be:
>   * Making sure it works properly regardless of the mounting scheme
>   * Perhaps offering easy (eg. menu) access to utilities to manage such
>     systems if available and appropriate
>
> > >   Another useful thing might be to somehow ID disks somehow (serial number? Can
> > > a non-privileged process get that?) to detect 'disk switches' and even allow
> > > two separate removable VFSs to be open at once (for example, I open a VFS
> > > on one floppy and another on another floppy, then copy a file from one floppy
> > > to the other..the VFS asks me to insert each floppy at the appropriate time).
> 
> The only way of putting a serial number on a disk is with filesystems
> that support it.  DOS disks formatted with version 5.0 and earler have no
> serial number.  I don't think Minix or Ext2 floppies do either.  Since any
> serial number would be dependant on the filesystem used on the floppy,
> this doesn't sound very feasable.

  Ah, ok.  I still wonder though ;) whether it would be possible to create
a hash table from the directory structure or some such thing.  Just idle
speculation at this point, though.

  The thing is--mount/umount is a wonderful system.  But it seems to work
much better for hard drives than for floppies.  In addition, Gnome is supposed
to make Unix systems easier to use.  That involves more than just putting
pretty pictures on standard UNIX tools (and Gnome has been quite good about
this everywhere except the disk-mount situation).  I don't see anyone suggesting
that making an Eterm transparent is going to make my mother use the shell (not
to pick on my mother..she's a wonderful person mostly but is not a
technophile). She can learn to mount and unmount disks..probably..but it's an
extra set of actions that most people are going to just be annoyed by, and when
they forget and their computer locks up..that's not good.

  The situation would be somewhat better if floppy drives behaved like CDs;
the CD drive refuses to open until you umount the CD.  But they don't..

  Does anyone know how MacOS X will handle this?  I know it's a BSD derivative
which means it'll mount/umount internally but how is Apple dealing with
removable stuff?  I'm almost sure that it won't *require* manual mounting
or unmounting.  Automounting, lockable drives (like my CD), and media-change
notification are my guesses..

-- 
All generalizations are dangerous.