doc: update the instructions to increase the size of a UOS disk image

Update the instructions on how to increase the size of a UOS disk image so that
the entire operation can be performed on the development host. This has the
advantage that it can be done completely offline (the UOS must be powered off
in fact) and no extra tools need to be installed in the UOS to do this.

Signed-off-by: Geoffroy Van Cutsem <geoffroy.vancutsem@intel.com>

doc/tutorials/increase-uos-disk-size.rst

@@ -18,12 +18,13 @@ broken down into three steps:
 #. Resize the ``rootfs`` partition
 #. Resize the filesystem
 
-Increase the virtual disk size
-******************************
-
 .. note::
 
-   This step **must** be performed while the User OS (UOS) is powered off.
+   These steps are performed directly on the UOS disk image. The UOS VM **must**
+   be powered off during this operation.
+
+Increase the virtual disk size
+******************************
 
 We will use the ``qemu-img`` tool to increase the size of the virtual disk
 (``uos.img``) file. On a Clear Linux system, you can install this tool using:
@@ -49,23 +50,65 @@ As an example, let us add 10GB of storage to our virtual disk image called
    You can choose any increment for the additional storage space. Check the
    ``qemu-img resize`` help for more information.
 
-Now that you have increased the size of the virtual disk, power up the Virtual
-Machine (VM) before moving to the next steps.
-
 Resize the ``rootfs`` partition
 *******************************
 
-Follow the `Resize the partition of the virtual disk <https://clearlinux.org/
-documentation/clear-linux/guides/maintenance/increase-virtual-disk-size#resize-
-the-partition-of-the-virtual-disk>`_ section to resize the partition hosting the
-UOS rootfs (typically ``/dev/sda3``).
+The next step is to modify the ``rootfs`` partition (in Clear Linux, it is
+partition 3) to use the additional space available. We will use the ``parted``
+tool and perform these steps:
+
+* Enter the ``parted`` tool
+* Press ``p`` to print the partition tables
+* A warning will be displayed, enter ``Fix``
+* Enter ``resizepart 3``
+* Enter the size of the disk (``19.9GB`` in our example)
+* Enter ``q`` to quit the tool
+
+Here is what the sequence looks like:
+
+.. code-block:: none
+
+   $ parted uos.img
+
+.. code-block:: console
+   :emphasize-lines: 5,7,9,19,20
+
+   WARNING: You are not superuser.  Watch out for permissions.
+   GNU Parted 3.2
+   Using /home/gvancuts/uos/uos.img
+   Welcome to GNU Parted! Type 'help' to view a list of commands.
+   (parted) p                                                                
+   Warning: Not all of the space available to /home/gvancuts/uos/uos.img appears to be used, you can fix the GPT to use all of the space (an extra 20971520 blocks) or continue with the current setting? 
+   Fix/Ignore? Fix                                                           
+   Model:  (file)
+   Disk /home/gvancuts/uos/uos.img: 19.9GB
+   Sector size (logical/physical): 512B/512B
+   Partition Table: gpt
+   Disk Flags: 
+
+   Number  Start   End     Size    File system     Name     Flags
+    1      1049kB  537MB   536MB   fat16           primary  boot, esp
+    2      537MB   570MB   33.6MB  linux-swap(v1)  primary
+    3      570MB   9160MB  8590MB  ext4            primary
+
+   (parted) resizepart 3                                                     
+   End?  [9160MB]? 19.9GB
+   (parted) q                 
 
 Resize the filesystem
 *********************
 
-Follow the `Resize the filesystem <https://clearlinux.org/documentation/
-clear-linux/guides/maintenance/increase-virtual-disk-size#resize-the-filesytem>`_
-section to resize the filesystem to use the entire storage capacity.
+The final step is to resize the ``rootfs`` filesystem to use the entire
+partition space.
+
+.. code-block:: none
+
+   $ LOOP_DEV=`sudo losetup -f -P --show uos.img`
+   $ PART_DEV=$LOOP_DEV
+   $ PART_DEV+="p3"
+   $ sudo e2fsck -f $PART_DEV
+   $ sudo resize2fs -p $PART_DEV
+   $ sudo losetup -d $LOOP_DEV
 
 Congratulations! You have successfully resized the disk, partition, and
-filesystem or your User OS.
+filesystem of your User OS.