daemon: Account for deleted store files when deduplication is on.

Previously, a store item that is a regular file would not be accounted
for in the 'bytesFreed' value computed by 'deletePath' because its
'st_nlink' count would always be >= 2.  This commit fixes that.

* nix/libutil/util.hh (deletePath): Add optional 'linkThreshold' argument.
* nix/libutil/util.cc (_deletePath): Add 'linkThreshold' argument and
honor it.  Pass it down in recursive call.
(deletePath): Add 'linkThreshold' and honor it.
* nix/libstore/gc.cc (LocalStore::deleteGarbage): Pass 'linkThreshold'
argument to 'deletePath', with a value of 2 when PATH is a store item
and deduplication is on.

1 files changed, 8 insertions, 1 deletions

diff --git a/nix/libstore/gc.cc b/nix/libstore/gc.cc
index 29b75aa875..5043963fa2 100644
--- a/nix/libstore/gc.cc
+++ b/nix/libstore/gc.cc
@@ -392,7 +392,14 @@ bool LocalStore::isActiveTempFile(const GCState & state,
 void LocalStore::deleteGarbage(GCState & state, const Path & path)
 {
     unsigned long long bytesFreed;
-    deletePath(path, bytesFreed);
+
+    /* When deduplication is on, store items always have at least two links:
+       the one at PATH, and one in /gnu/store/.links.  In that case, increase
+       bytesFreed when PATH has two or fewer links.  */
+    size_t linkThreshold =
+	(settings.autoOptimiseStore && isStorePath(path)) ? 2 : 1;
+
+    deletePath(path, bytesFreed, linkThreshold);
     state.results.bytesFreed += bytesFreed;
 }