bug#37569: Mount does not honor 'user' option.

[Diego Nicola Barbato <dnbarbato@posteo.de>]

Hey Guix,

I have added the following to `file-systems' in my operating-system
config:

--8<---------------cut here---------------start------------->8---
(file-system                                                                   
  (device "127.0.0.1")                                                         
  (mount-point "/home/diego/inf")                                              
  (type "9p")                                                                  
  (options "noextend,trans=tcp,dfltuid=1000,dfltgid=998,port=9001,user,nofail")
  (mount? #f))
--8<---------------cut here---------------end--------------->8---

It works almost as expected except that when I try to mount the file
system as a regular user (which is what the option 'user' is supposed to
allow) I get:

  $ LC_ALL=C mount inf
  mount: /home/diego/inf: must be superuser to use mount.

The command succeeds if I run it as root.

The following steps reproduce the issue without using a 9p file system:

1. Prepare a file system on a loopback device:

  $ dd if=/dev/zero of=foo.img bs=1024 count=524288
  $ udisksctl loop-setup --file foo.img
  Mapped file foo.img as /dev/loop0.
  $ sudo mkfs.ext4 -L foofs /dev/loop0

2. Add the following line to /etc/fstab replacing <name> with something
more appropriate:

  LABEL=foofs /home/<name>/foofs ext4 defaults,user

3. Try to mount the filesystem as an unprivileged user (This should work
and does work on e.g. Debian 10):

  $ mkdir foofs
  $ LC_ALL=C mount foofs
  mount: /home/<name>/foofs: must be superuser to use mount.

4. Try it with sudo to confirm that everything else works as expected:

  $ sudo mount foofs
  $ ls foofs
  lost+found/

Regards,

Diego