Make roots a map of store paths to pinning links

This new structure makes more sense as there may be many sources rooting
the same store path. Many profiles can reference the same path but this
is even more true with /proc/<pid>/maps where distinct pids can and
often do map the same store path.
This implementation is also more efficient as the `Roots` map contains
only one entry per rooted store path.

1 files changed, 12 insertions, 7 deletions

diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index faa23b2686..014378d27e 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -477,14 +477,19 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         Roots roots = store->findRoots();
         logger->stopWork();
-        to << roots.size();
+        size_t total_length = 0;
+        for (auto & root : roots)
+            total_length += root.second.size();
+        to << total_length;
         int n = 0;
-        for (auto & i : roots) {
-            // Obfuscate 'memory' roots as they exposes information about other users,
-            if (i.first.rfind("{memory:", 0) == 0) {
-               to << fmt("{memory:%d}", n++) << i.second;
-            } else {
-               to << i.first << i.second;
+        for (auto & [target, links] : roots) {
+            for (auto & link : links) {
+                // Obfuscate 'memory' roots as they expose information about other users,
+                if (link.rfind("{memory:", 0) == 0) {
+                    to << fmt("{memory:%d}", n++) << target;
+                } else {
+                    to << link << target;
+                }
             }
         }
         break;