Reserve some disk space for the garbage collector

We can't open a SQLite database if the disk is full.  Since this
prevents the garbage collector from running when it's most needed, we
reserve some dummy space that we can free just before doing a garbage
collection.  This actually revives some old code from the Berkeley DB
days.

Fixes #27.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 0fd759b07b..cbcf860543 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -43,7 +43,7 @@ RemoteStore::RemoteStore()
 }
 
 
-void RemoteStore::openConnection()
+void RemoteStore::openConnection(bool reserveSpace)
 {
     if (initialised) return;
     initialised = true;
@@ -75,6 +75,8 @@ void RemoteStore::openConnection()
         if (GET_PROTOCOL_MAJOR(daemonVersion) != GET_PROTOCOL_MAJOR(PROTOCOL_VERSION))
             throw Error("Nix daemon protocol version not supported");
         writeInt(PROTOCOL_VERSION, to);
+        if (GET_PROTOCOL_MINOR(daemonVersion) >= 11)
+            writeInt(reserveSpace, to);
         processStderr();
     }
     catch (Error & e) {
@@ -462,7 +464,7 @@ Roots RemoteStore::findRoots()
 
 void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
 {
-    openConnection();
+    openConnection(false);
     
     writeInt(wopCollectGarbage, to);
     writeInt(options.action, to);