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, 4 insertions, 2 deletions

diff --git a/nix/libutil/util.hh b/nix/libutil/util.hh
index 6a6e07c478..9e3c14bdd4 100644
--- a/nix/libutil/util.hh
+++ b/nix/libutil/util.hh
@@ -94,10 +94,12 @@ void writeLine(int fd, string s);
 
 /* Delete a path; i.e., in the case of a directory, it is deleted
    recursively.  Don't use this at home, kids.  The second variant
-   returns the number of bytes and blocks freed. */
+   returns the number of bytes and blocks freed, and 'linkThreshold' denotes
+   the number of links under which a file is accounted for in 'bytesFreed'.  */
 void deletePath(const Path & path);
 
-void deletePath(const Path & path, unsigned long long & bytesFreed);
+void deletePath(const Path & path, unsigned long long & bytesFreed,
+    size_t linkThreshold = 1);
 
 /* Create a temporary directory. */
 Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",