Auto-configure swap

Create a swapfile and configure it to be used for swap, immediately and
on boot; defaults to half the size of RAM. See attribute for overriding
configs to tune size or swappiness.

site-cookbooks/kosmos_kvm/attributes/default.rb

@@ -11,3 +11,10 @@ node.default["kosmos_kvm"]["host"]["qemu_base_image"] = {
 node.default["kosmos_kvm"]["backup"]["schedule"] = "0/3:00"
 # Node/VM names excluded from backups
 node.default["kosmos_kvm"]["backup"]["nodes_excluded"] = []
+
+node.default["kosmos_kvm"]["guest"]["swap"] = {
+  "enabled" => true,    # set to false to disable swap on a guest
+  "size_mb" => nil,     # nil => auto (half of RAM); integer => fixed MB; 0 => disabled
+  "path" => "/swapfile",
+  "swappiness" => nil   # nil => leave kernel default; e.g. 10 to tune
+}

site-cookbooks/kosmos_kvm/recipes/guest.rb

@@ -8,3 +8,20 @@ package %w(qemu-guest-agent)
 service "qemu-guest-agent" do
   action [:enable, :start]
 end
+
+swap_cfg = node["kosmos_kvm"]["guest"]["swap"]
+
+if swap_cfg["enabled"] && swap_cfg["size_mb"] != 0
+  size = swap_cfg["size_mb"] ||
+         (node["memory"]["total"].to_i / 2 / 1024) # kB -> MB, half RAM
+
+  # The resource only creates/activates the swapfile if it is not already
+  # active; an existing active swapfile is left untouched (size is NOT
+  # reconciled to current RAM).
+  swap_file swap_cfg["path"] do
+    size       size
+    persist    true
+    swappiness swap_cfg["swappiness"] if swap_cfg["swappiness"]
+    action     :create
+  end
+end