cc_disk_setup.py: fix MBR single partition creation (#1932)

Fixes the creation of single partitions on MBR devices. Currently this
fails with the following debug output:

cc_disk_setup.py[DEBUG]: Calculating partition layout
cc_disk_setup.py[DEBUG]:    Layout is: 0,
cc_disk_setup.py[DEBUG]: Creating partition table on /dev/sdb
subp.py[DEBUG]: Running command ['/sbin/sfdisk', '--Linux', '--unit=S',
'--force', '/dev/sdb'] with allowed return codes [0] (shell=False,
capture=True)
util.py[DEBUG]: Creating partition on /dev/sdb took 0.237 seconds
util.py[WARNING]: Failed partitioning operation
Failed to partition device /dev/sdb
Unexpected error while running command.
Command: ['/sbin/sfdisk/', '--Linux', '--unit=S', '--force', '/dev/sdb']
Exit code: 1
Reason: -
Stdout: Checking that no-one is using this disk right now ... OK

        Disk /dev/sdb: 16 MiB, 16777216 bytes, 32768 sectors
        Disk model: HARDDISK
        Units: sectors of 1 * 512 = 512 bytes
        Sector size (logical/physical): 512 bytes / 512 bytes
        I/O size (minimum/optimal): 512 bytes / 512 bytes

        >>> Created a new DOS disklabel with disk identifier 0xb3604c9a.
        /dev/sdb1: Leaving.
Stderr: sfdisk: --Linux option is unnecessary and deprecated
        Start sector 0 out of range.
        Failed to add #1 partition: Result not representable
util.py[DEBUG]: Failed partitioning operation

On a BIOS/MBR partitioned device the 1st partition cannot start at sector
0 as this is reserved for the MBR.

Documentation clarifications/corrections and additional examples added.

Also remove "--Linux" and "--unit=S" options from sfdisk calls, these
options have been deprecated since October 2014.

Note: This is not a change of behavior because the change provoking
the error was introduced in util-linux 2.26 in Xenial. Thus, every
supported cloud-init version fails.

LP: #1851438

2 files changed, 14 insertions, 6 deletions

diff --git a/cloudinit/config/cc_disk_setup.py b/cloudinit/config/cc_disk_setup.py
index 71d52d3d..5ec5c793 100644
--- a/cloudinit/config/cc_disk_setup.py
+++ b/cloudinit/config/cc_disk_setup.py
@@ -80,6 +80,10 @@ meta: MetaSchema = {
                 table_type: gpt
                 layout: [[100, 82]]
                 overwrite: true
+              /dev/sdd:
+                table_type: mbr
+                layout: true
+                overwrite: true
             fs_setup:
             - label: fs1
               filesystem: ext4
@@ -91,10 +95,14 @@ meta: MetaSchema = {
             - label: swap
               device: swap_disk.1
               filesystem: swap
+            - label: fs3
+              device: /dev/sdd1
+              filesystem: ext4
             mounts:
             - ["my_alias.1", "/mnt1"]
             - ["my_alias.2", "/mnt2"]
             - ["swap_disk.1", "none", "swap", "sw", "0", "0"]
+            - ["/dev/sdd1", "/mnt3"]
             """
         )
     ],
@@ -605,8 +613,8 @@ def get_partition_mbr_layout(size, layout):
     """
 
     if not isinstance(layout, list) and isinstance(layout, bool):
-        # Create a single partition
-        return "0,"
+        # Create a single partition, default to Linux
+        return ",,83"
 
     if (len(layout) == 0 and isinstance(layout, list)) or not isinstance(
         layout, list
@@ -741,7 +749,7 @@ def exec_mkpart_mbr(device, layout):
     types, i.e. gpt
     """
     # Create the partitions
-    prt_cmd = [SFDISK_CMD, "--Linux", "--unit=S", "--force", device]
+    prt_cmd = [SFDISK_CMD, "--force", device]
     try:
         subp.subp(prt_cmd, data="%s\n" % layout)
     except Exception as e:
@@ -968,7 +976,7 @@ def mkfs(fs_cfg):
         odevice = device
         LOG.debug("Identifying device to create %s filesytem on", label)
 
-        # any mean pick the first match on the device with matching fs_type
+        # 'any' means pick the first match on the device with matching fs_type
         label_match = True
         if partition.lower() == "any":
             label_match = False
diff --git a/cloudinit/config/schemas/schema-cloud-config-v1.json b/cloudinit/config/schemas/schema-cloud-config-v1.json
index 7ff80ce3..42745b28 100644
--- a/cloudinit/config/schemas/schema-cloud-config-v1.json
+++ b/cloudinit/config/schemas/schema-cloud-config-v1.json
@@ -1180,7 +1180,7 @@
               },
               "device": {
                 "type": "string",
-                "description": "Specified either as a path or as an alias in the format ``<alias name>.<y>`` where ``<y>`` denotes the partition number on the device. If specifying device using the ``<device name>.<partition number>`` format, the value of ``partition`` will be overwritten."
+                "description": "Specified either as a path or as an alias in the format ``<alias name>.<y>`` where ``<y>`` denotes the partition number on the device. If specifying device using the ``<alias name>.<partition number>`` format, the value of ``partition`` will be overwritten."
               },
               "partition": {
                 "type": [
@@ -1197,7 +1197,7 @@
                     ]
                   }
                 ],
-                "description": "The partition can be specified by setting ``partition`` to the desired partition number. The ``partition`` option may also be set to ``auto``, in which this module will search for the existence of a filesystem matching the ``label``, ``type`` and ``device`` of the ``fs_setup`` entry and will skip creating the filesystem if one is found. The ``partition`` option may also be set to ``any``, in which case any file system that matches ``type`` and ``device`` will cause this module to skip filesystem creation for the ``fs_setup`` entry, regardless of ``label`` matching or not. To write a filesystem directly to a device, use ``partition: none``. ``partition: none`` will **always** write the filesystem, even when the ``label`` and ``filesystem`` are matched, and ``overwrite`` is ``false``."
+                "description": "The partition can be specified by setting ``partition`` to the desired partition number. The ``partition`` option may also be set to ``auto``, in which this module will search for the existence of a filesystem matching the ``label``, ``filesystem`` and ``device`` of the ``fs_setup`` entry and will skip creating the filesystem if one is found. The ``partition`` option may also be set to ``any``, in which case any filesystem that matches ``filesystem`` and ``device`` will cause this module to skip filesystem creation for the ``fs_setup`` entry, regardless of ``label`` matching or not. To write a filesystem directly to a device, use ``partition: none``. ``partition: none`` will **always** write the filesystem, even when the ``label`` and ``filesystem`` are matched, and ``overwrite`` is ``false``."
               },
               "overwrite": {
                 "type": "boolean",