First unmounter

src/lib/installation/unmounter.rb

@@ -0,0 +1,148 @@
+# encoding: utf-8
+# ------------------------------------------------------------------------------
+# Copyright (c) 2021 SUSE LLC
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of version 2 of the GNU General Public License as published by the
+# Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+#
+# ------------------------------------------------------------------------------
+
+require "yast"
+
+module Installation
+  # Class to handle unmounting all mounts from the given subtree on in the
+  # right order.
+  #
+  # This uses /proc/mounts by default to find active mounts, but it can also be
+  # fed from other files or line by line for testability. It stores all
+  # necessary unmount actions so they can be executed all at once, and they can
+  # also be inspected without the execute step. This is intended for logging,
+  # debugging and testing.
+  #
+  # This relies on /proc/mounts already containing the entries in canonical
+  # order (which it always does), i.e. in the mount hierarchy from top to
+  # bottom. If you add entries manually, make sure to maintain that order.
+  #
+  class Unmounter
+    include Yast::Logger
+    # @return [Array<Mount>] Relevant mounts to unmount
+    attr_reader :mounts
+
+    # Helper class to represent one mount, i.e. one entry in /proc/mounts.
+    class Mount
+      attr_reader :device, :mount_path, :fs_type, :mount_opt
+
+      def initialize(device, mount_path, fs_type = "", mount_opt = "")
+        @device = device
+        @mount_path = mount_path
+        @fs_type = fs_type
+        @mount_opt = mount_opt
+      end
+
+      # Check if this is a mount for a btrfs.
+      # @return [Boolean] true if btrfs, false if not
+      def btrfs?
+        return false if @fs_type.nil?
+
+        @fs_type.downcase == "btrfs"
+      end
+
+      # Format this mount as a string for logging.
+      def to_s
+        "<Mount #{@device} -> #{@mount_path} type #{@fs_type}>"
+      end
+    end
+
+    # Unmounter constructor.
+    #
+    # @param mnt_prefix [String] Prefix which paths should be unmounted.
+    #
+    # @param mounts_file_name [String] what to use instead of /proc/mounts.
+    #   Use an empty string (not nil!) to not read anything at all yet
+    #   (but in that case, use read_mounts_file or add_mount later).
+    #
+    def initialize(mnt_prefix, mounts_file_name = nil)
+      @mnt_prefix = mnt_prefix || "/mnt"
+      mounts_file_name ||= "/proc/mounts"
+      @mounts = []
+      read_mounts_file unless mounts_file_name.empty?
+    end
+
+    # Read a mounts file like /proc/mounts and add the relevant entries to the
+    # mounts stored in this class.
+    #
+    def read_mounts_file(file_name)
+      open(file_name).each { |line| add_mount(line) }
+    end
+
+    # Parse one entry of /proc/mounts and add it to @mounts
+    # if it meets the criteria (mount prefix, no btrfs subvolume)
+    #
+    # @param line [String] one line of /proc/mounts
+    # @return [Mount,nil] parsed mount
+    #
+    def add_mount(line)
+      mount = parse_mount(line)
+      return nil if mount.nil? # Empty or comment
+
+      return nil unless mount_path.start_with(@mnt_prefix)
+
+      if mount.btrfs? && mount_for_device(mount.device)
+        # We already have a mount for a Btrfs on this device,
+        # so any more mount for that device must be a subvolume.
+        #
+        # Notice that this relies on /proc/mounts being in the correct order:
+        # Btrfs main mount first, all its subvolumes after that.
+        log.info("Ignoring btrfs subvolume #{mount}")
+        return nil
+      end
+
+      log.info("Adding #{mount}")
+      @mounts << mount
+      mount
+    end
+
+    # Parse one entry of /proc/mounts.
+    #
+    # @param line [String] one line of /proc/mounts
+    # @return [Mount,nil] parsed mount
+    def parse_mount(line)
+      line.strip!
+      return nil if line.empty? || line.start_with("#")
+
+      (device, mount_path, fs_type, mount_opt) = line.split
+      return Mount.new(device, mount_path, fs_type, mount_opt)
+    end
+
+    # Return the mount for a specified device or nil if there is none.
+    # @param device [String]
+    # @return [Mount,nil] Matching mount
+    def mount_for_device(device)
+      @mounts.find { |mount| mount.device == device }
+    end
+
+    # Return the paths to be unmounted in the correct unmount order.
+    #
+    # This makes use of the fact that /proc/mounts is already sorted in
+    # canonical order, i.e. from toplevel mount points to lower level ones.
+    #
+    # @return [Array<String>] paths
+    def unmount_paths
+      paths = @mounts.map { |mount| mount.mount_path }
+      paths.reverse
+    end
+
+    def execute
+      unmount_paths.each do |path|
+        log.info("Unmounting #{path}")
+        Yast::Execute.locally!("/usr/bin/umount", path)
+      end
+    end
+  end
+end
+