Re: request for patches: showing mount options

quoted

The removal of /etc/mtab in favor of /proc/mounts is a new requirement, 
and is not as trivial as you might hope.  Internally the NFS client 
represents the mount options as a binary data structure, and it contains 
only the information that has traditionally been passed into the kernel 
by the current mount command.  The user-space-only options are not 
passed to the kernel nor stored in the data structure.

Adding facilities to store information about every possible mount 
option, including the user-space-only ones, will take a bit of time, but 
is possible, if not straightforward.  We just have to understand all the 
dependencies.

 I still have doubts. The removal of /etc/mtab is nice, but a little
 unreal wish. Do we really want to store non-kernel data (options) in
 kernel? What about options that are not closely related to any
 filesystem -- for example "loop="?

"loop=DEV" is special, we've already talked about that.

For example if we have an mtab entry like this:

  /dir/foo.iso /mnt/image ext3 rw,loop=/dev/loop/0 0 0

It says: /dev/loop/0 has been automatically set up by mount(8) from
/dir/foo.iso and so needs to be torn down by umount(8).  It is not a
property of the mount, rather the property of the device.

So what we really want is a file to store this, and only this info:

/var/lib/mount/loop:

/dev/loop/0 /dir/foo.iso
/dev/loop/2 /dir/bar.img
...

Notice, there's nothing about the _mountpoint_ in this file.

 Maybe we can replace /etc/mtab with something more useful
 (e.g. /var/run/mount/<mntid>.tab) for really user-space-only information.

The problem with storing mount options in userspace is that
unprivileged mounts/umounts won't work in the presense of those, we
cannot _force_ an unprivileged user to update a file.

So we want to avoid storing options in userspace as long as possible.

Miklos