From 40770405e32fc0a2edad52a64963f9beff0692c7 Mon Sep 17 00:00:00 2001
From: Gregor Kleen <gkleen@yggdrasil.li>
Date: Mon, 9 Apr 2018 15:04:42 +0200
Subject: Hold lock while snapshot exists

---
 custom/lvm-snapshots.nix | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

(limited to 'custom')

diff --git a/custom/lvm-snapshots.nix b/custom/lvm-snapshots.nix
index af8b61bb..afa5a9d6 100644
--- a/custom/lvm-snapshots.nix
+++ b/custom/lvm-snapshots.nix
@@ -71,12 +71,19 @@ in {
 
       unitConfig = {
         StopWhenUnneeded = !scfg.persist;
+        AssertPathIsDirectory = "/var/lock";
       };
 
-      path = with pkgs; [ devicemapper ];
+      path = with pkgs; [ devicemapper utillinux ];
       
       script = ''
-        lvcreate -s ${scfg.cowSize} --name ${snapshotName name} ${scfg.VG}/${scfg.LV}
+        (
+          flock -xn 9 || exit 1
+          
+          lvcreate -s ${scfg.cowSize} --name ${snapshotName name} ${scfg.VG}/${scfg.LV}
+
+          sleep infinity &
+        ) 9>/var/lock/lvm-snapshot.${scfg.VG}
       '';
 
       preStop = ''
@@ -84,8 +91,7 @@ in {
       '';
 
       serviceConfig = with pkgs; {
-        Type = "oneshot";
-        RemainAfterExit = true;
+        Type = "forking";
       };
     }) cfg.snapshots;
 
-- 
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