From 951ddfb72a89b4fe656a8000250202483d24d92d Mon Sep 17 00:00:00 2001
From: Adriaan de Groot <groot@kde.org>
Date: Wed, 1 Dec 2021 23:06:02 +0100
Subject: [PATCH 1/3] [mount] Experimental: accept 'no' for subvolumes

If there is no subvolume set, skip creation of that subvolume.
This allows root to be on a bare FS, without a tag or subvolume
name. To achieve this, use
    subvolume: no
(no quotes there) in the YAML.
---
 src/modules/mount/main.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/modules/mount/main.py b/src/modules/mount/main.py
index 900342e6d..f186b0d26 100644
--- a/src/modules/mount/main.py
+++ b/src/modules/mount/main.py
@@ -191,6 +191,8 @@ def mount_partition(root_mount_point, partition, partitions):
         libcalamares.globalstorage.insert("btrfsSubvolumes", btrfs_subvolumes)
         # Create the subvolumes that are in the completed list
         for s in btrfs_subvolumes:
+            if not s["subvolume"]:
+                continue
             subprocess.check_call(["btrfs", "subvolume", "create",
                                    root_mount_point + s["subvolume"]])
             if s["mountPoint"] == "/":

From 96ccf256b207fa3f41dae816d31b4686b492ec1c Mon Sep 17 00:00:00 2001
From: Adriaan de Groot <groot@kde.org>
Date: Thu, 2 Dec 2021 22:02:14 +0100
Subject: [PATCH 2/3] [mount] Add documentation to the config file

---
 src/modules/mount/mount.conf | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/modules/mount/mount.conf b/src/modules/mount/mount.conf
index 6168e97cc..84dca05a7 100644
--- a/src/modules/mount/mount.conf
+++ b/src/modules/mount/mount.conf
@@ -42,15 +42,24 @@ extraMountsEfi:
       mountPoint: /sys/firmware/efi/efivars
 
 # Btrfs subvolumes to create if root filesystem is on btrfs volume.
-# If mountpoint is mounted already to another partition, it is ignored.
+# If *mountpoint* is mounted already to another partition, it is ignored.
 # Separate subvolume for swapfile is handled separately and automatically.
+#
+# It is possible to prevent subvolume creation -- this is likely only relevant
+# for the root (/) subvolume -- by giving an empty string as a subvolume
+# name. In this case no subvolume will be created. When using snapper as
+# a rollback mechanism, it is recommended to **not** create a subvolume
+# for root.
 
 btrfsSubvolumes:
     - mountPoint: /
       subvolume: /@
+      # As an alternative:
+      #
+      # subvolume: ""
     - mountPoint: /home
       subvolume: /@home
     - mountPoint: /var/cache
       subvolume: /@cache
     - mountPoint: /var/log
-      subvolume: /@log
\ No newline at end of file
+      subvolume: /@log

From f26c81700d7c34b5411038acd245ef797f95fdd6 Mon Sep 17 00:00:00 2001
From: Adriaan de Groot <groot@kde.org>
Date: Thu, 2 Dec 2021 22:08:17 +0100
Subject: [PATCH 3/3] [fstab] Suppress empty subvol= options in fstab

---
 src/modules/fstab/main.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/modules/fstab/main.py b/src/modules/fstab/main.py
index 261d3cadb..426761453 100644
--- a/src/modules/fstab/main.py
+++ b/src/modules/fstab/main.py
@@ -258,7 +258,8 @@ class FstabGenerator(object):
         if mount_point == "/":
             self.root_is_ssd = is_ssd
 
-        if filesystem == "btrfs" and "subvol" in partition:
+        # If there's a set-and-not-empty subvolume set, add it
+        if filesystem == "btrfs" and partition.get("subvol",None):
             options = "subvol={},".format(partition["subvol"]) + options
 
         if has_luks: