Re: concurrent X users and gnome-volume-manager
On Sat, Dec 18, 2004 at 04:42:10PM +1100, Graham Williams wrote:
> Thanks. Looks like I'm out of luck with g-v-m in this setup then.
> Back to my Disk Mounter applets!
I was looking a bit more into this, just out curiosity.
The use of pmount is hard-coded in g-v-m:
$ strings /usr/bin/gnome-volume-manager | grep pmount
/usr/bin/pmount-hal %h
so no configurability there.
pmount's "policy" is also hard-coded (look at the source)[0], no
configurability here either.
Part of pmount's policy is that you need to be able to run pmount in
order to mount a device. This leads to the "you need to be in the
plugdev to mount a device" default requirement.
An entry in /etc/fstab overrides pmount's policy.
In order to be able to umount a device, pmount requires that this
device has been mounted by you. This is enforced by checking /etc/mtab
and parsing the mount options looking for "uid=n". n needs to be the
uid of the user trying to unmount the device. I wonder how mount
enforces the user and users option.
In short, your problem, as I see it, is this:
* pmount's policy is that if you can run pmount and fulfill certain
criteria, you can mount a device.
* pumount's policy is that you can run pumount, you are the user who
mounted the device and fulfill certain criteria, you can unmount
the device.
The problem with g-v-m is that if you have two g-v-m's running, both
will get messages from HAL which means that they will race for mounting
the device. As I said before, one of them should go to sleep, but even
that solution is highly unsatisfactory.
Marcelo
[0] Here I have to say that in the grand tradition of documenting
programs incompletely, what pmount actually does is a bit more than
what the manpages say it does. For starters, it supports a certain
subset of filesystems (all of them likely to be present in
removable media); it creates directories with a mode of 0755
(modifies by the user's umask); it constructs the arguments it
passes to mount in a certain way and assumes that the information
found in /etc/mtab has been constructed in this way; it requires
devices to be under /dev and it follows symlinks in the device name
that it gets (to enforce this among other things), which is not
quite consistent with this wording:
pmount device [ label ]
This will mount device to a directory below /media if policy
is met (see below). If label is given, the mount point will be
/media/label, otherwise it will be /media/device.
I expected "pmount /dev/dvd" to mount the dvd under /media/dvd
(following the wording above), instead it ends up in /media/hdc.
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