home/environ: vtmp: implement vtmp-restore

1 files changed, 109 insertions, 12 deletions

diff --git a/home/environ/vtmp.nix b/home/environ/vtmp.nix
index e15778d..7513f2d 100644
--- a/home/environ/vtmp.nix
+++ b/home/environ/vtmp.nix
@@ -7,7 +7,10 @@
 with lib; let
   cfg = config.local.environ;
 
-  vtmp-sync = pkgs.writeShellScript "vtmp-sync" ''
+  prelude = pkgs.writeText "vtmp-prelude" ''
+    set -o errexit
+    set -o pipefail
+
     if [ $# -ne 3 ]; then
       echo "usage: $0 <remote hostname> <local hostname> <boot id>" >&2
       exit 1
@@ -15,8 +18,9 @@ with lib; let
 
     local="$2"
     remote="$1"
-    boot_id="$(echo "$3" | ${pkgs.coreutils}/bin/head -c8)"
+    boot_id="$(echo "$3" | head -c8)"
 
+    ssh="${lib.getExe pkgs.openssh} -o BatchMode=yes"
     rsync="${lib.getExe pkgs.rsync}"
 
     cd "$HOME/vtmp"
@@ -27,16 +31,91 @@ with lib; let
     rsync_opts+=("--open-noatime")
     rsync_opts+=("--preallocate")
     rsync_opts+=("--max-size=1G")
-    rsync_opts+=("--rsh=${lib.getExe pkgs.openssh} -o BatchMode=yes")
-    rsync_opts+=("--log-file=$remote/.rsync.log")
-    rsync_opts+=("--filter=- /$local.$boot_id/")
+    rsync_opts+=("--rsh=$ssh")
+    rsync_opts+=("--log-file=.rsync-$remote.log")
     rsync_opts+=("--filter=- /$remote/")
+    rsync_opts+=("--filter=- /$remote")
+  '';
+
+  vtmp-restore = pkgs.writeShellScript "vtmp-restore" ''
+    source ${prelude}
+
+    [ ! -L .restore ] || exit 0
+
+    parent="$($ssh -- "$remote" " \
+        set -o errexit; \
+        set -o pipefail; \
+        \
+        mkdir -p -- \"vtmp/$local/$boot_id\"; \
+        ln -fsT -- ../.. \"vtmp/$local/$boot_id/$remote\"; \
+        \
+        last=\"\$(readlink -qe -- \"vtmp/$local/last\")\" || { echo \"$boot_id\"; exit 0; }; \
+        if [ \"\$last\" != \"$boot_id\" -a ! -L \"vtmp/$local/$boot_id/.last\" ]; then \
+            ln -fsT -- \"$remote/$local/\$last\" \"vtmp/$local/$boot_id/.last\"; \
+        fi; \
+        \
+        parent=\"\$(realpath -qe --relative-to=\"vtmp/$local\" -- \"vtmp/$local/last/.save\")\" ||  \
+            { echo \"$boot_id\"; exit 0; }; \
+        \
+        if [ \"vtmp/$local/$boot_id/.last\" -nt \"vtmp/$local/\$parent/.last\" ]; then \
+            mv -T --exchange --no-copy \"vtmp/$local\"/{\"\$parent\",\"$boot_id\"}/.last; \
+        fi; \
+        \
+        echo \"\$parent\"; \
+    ")"
+
+    if [ -z "$parent" ]; then
+        echo "$0: error: empty parent" >&2
+        exit 1
+    fi
+
+    # Pull restored state from $remote
+    # Note that $parent can equal $boot_id if ~/vtmp got cleared after saving with no reboot
+    rsync_opts+=("--filter=- /.save")
+    rsync_opts+=("--filter=- /.restore")
+    $rsync "''${rsync_opts[@]}" -- "$remote:vtmp/$local/$parent/" ./
+
+    $ssh -- "$remote" " \
+        set -o errexit; \
+        set -o pipefail; \
+        \
+        touch -cr \"vtmp/$local/$parent\" \"vtmp/$local/$boot_id\"; \
+        if [ \"$parent\" != \"$boot_id\" ]; then \
+            ln -fsT -- \"$remote/$local/$parent\" \"vtmp/$local/$boot_id/.save\"; \
+        fi; \
+        \
+        ln -fsT -- \"$boot_id\" \"vtmp/$local/last\"; \
+        \
+        if [ \"$parent\" != \"$boot_id\" ]; then \
+            rm -f \"vtmp/$local/$parent/.save\"; \
+            \
+            for link in .restore; do \
+                if [ -L \"vtmp/$local/$parent/\$link\" ]; then \
+                    mv -T \"vtmp/$local\"/{\"$parent\",\"$boot_id\"}/\"\$link\"; \
+                fi; \
+            done; \
+            \
+            touch -c \"vtmp/$local/$parent\"; \
+            mv -T --exchange --no-copy \"vtmp/$local\"/{\"$parent\",\"$boot_id\"}; \
+        fi; \
+    "
+
+    [ "$parent" != "$boot_id" ] && target="$remote/$local/$parent" || target=.
+    ln -fsT -- "$target" .restore
+  '';
+
+  vtmp-sync = pkgs.writeShellScript "vtmp-sync" ''
+    source ${prelude}
 
     # Push to $remote from $local
-    "$rsync" "''${rsync_opts[@]}" -- ./ "$remote:vtmp/$local.$boot_id/"
+    rsync_opts+=("--delete")
+    $rsync "''${rsync_opts[@]}" -- ./ "$remote:vtmp/$local/$boot_id/"
 
     # Pull from $remote to $local
-    "$rsync" "''${rsync_opts[@]}" -- "$remote:vtmp/" "./$remote/"
+    rsync_opts+=("--filter=- /$local/$boot_id/")
+    $rsync "''${rsync_opts[@]}" -- "$remote:vtmp/" "./$remote/"
+
+    ln -fsT ../.. "./$remote/$local/$boot_id"
   '';
 in {
   options.local.environ = {
@@ -77,13 +156,31 @@ in {
           };
         };
 
-        services.vtmp-sync = {
-          Unit = {
-            OnFailure = ["vtmp-sync-failure.target"];
+        services = {
+          vtmp-restore = {
+            Unit = {
+              ConditionPathIsSymbolicLink = ["!%t/vtmp/.restore"];
+            };
+
+            Service = {
+              Type = "oneshot";
+              ExecStart = "${vtmp-restore} ${cfg.vtmpSyncHost} %l %b";
+              Environment = ["PATH=${lib.makeBinPath [pkgs.coreutils]}"];
+            };
           };
 
-          Service = {
-            ExecStart = "${vtmp-sync} ${cfg.vtmpSyncHost} %l %b";
+          vtmp-sync = {
+            Unit = {
+              After = ["vtmp-restore.service"];
+              Requires = ["vtmp-restore.service"];
+              OnFailure = ["vtmp-sync-failure.target"];
+            };
+
+            Service = {
+              Type = "oneshot";
+              ExecStart = "${vtmp-sync} ${cfg.vtmpSyncHost} %l %b";
+              Environment = ["PATH=${lib.makeBinPath [pkgs.coreutils]}"];
+            };
           };
         };