Use PARTLABEL instead of LABEL

Using a label on the partition instead of on the file system has the
advantage of decoupling the label information from the file system which
will persist even to formatting the file system for example. Using
PARTLABEL is in general a more robust approach.

This patch also replaces `e2label` by `lsblk` as the former does not
require root permissions and also produces json output making it more
reliable to parse.

Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>

tools/psdk

@@ -24,6 +24,7 @@ import re
 import tempfile
 from string import Template
 import errno
+import json
 
 BKP_EXTENSION = ".PSDK"
 DISK_LABEL = "sdk-persistent"
@@ -111,7 +112,7 @@ class Disk:
         """Format the partition using ext4"""
 
         print("Will format the persistent storage partition...")
-        command = ["sudo", "mkfs.ext4", "-F", "-L", DISK_LABEL, self.partpath]
+        command = ["sudo", "mkfs.ext4", "-F", self.partpath]
         result = _run(command)
         print(result.stdout.decode())
 
@@ -121,7 +122,7 @@ class Disk:
         command = ["sudo", "mkdir", "-p", MOUNT_POINT]
         _run(command)
 
-        command = ["sudo", "mount", "-L", DISK_LABEL, MOUNT_POINT]
+        command = ["sudo", "mount", "PARTLABEL=" + DISK_LABEL, MOUNT_POINT]
         _run(command)
 
     def _part(self):
@@ -136,6 +137,13 @@ class Disk:
         # Give the kernel a moment to update the partition table
         time.sleep(3)
 
+        # Changes the label of partition 1 to DISK_LABEL
+        command = ["sudo", "sfdisk", "--part-label", self.diskpath, "1", DISK_LABEL]
+        _run(command)
+
+        # Give the kernel another moment to update the partition table
+        time.sleep(3)
+
     def _umount(self):
         """Unmount the fs"""
 
@@ -189,13 +197,13 @@ class Disk:
         if not os.path.exists(self.partpath):
             return False
 
-        command = ["sudo", "/sbin/e2label", self.partpath]
+        command = ["lsblk", "--json", "-o", "fstype,partlabel", self.partpath]
         result = _run(command)
 
-        part_uuid = result.stdout.decode().split("'")[1]
-
-        if part_uuid == DISK_LABEL:
-            return True
+        jpart_label = json.loads(result.stdout.decode())
+        if jpart_label["blockdevices"][0]["partlabel"] == DISK_LABEL:
+            if jpart_label["blockdevices"][0]["fstype"] == "ext4":
+                return True
 
         return False
 
@@ -220,7 +228,7 @@ def update_fstab():
 
     new_fstab = ""
     old_home_uuid = ""
-    new_home_line = "LABEL=" + DISK_LABEL + "\t/home\text4\tdefaults\t0\t0"
+    new_home_line = "PARTLABEL=" + DISK_LABEL + "\t/home\text4\tdefaults\t0\t0"
 
     with open("/etc/fstab", "rt") as fstab:
         for line in fstab: