* A GC setting `gc-keep-outputs' to specify whether output paths of

derivations should be kept.

src/libmain/Makefile.am

@@ -7,5 +7,6 @@ AM_CXXFLAGS = \
  -DNIX_DATA_DIR=\"$(datadir)\" \
  -DNIX_STATE_DIR=\"$(localstatedir)/nix\" \
  -DNIX_LOG_DIR=\"$(localstatedir)/log/nix\" \
+ -DNIX_CONF_DIR=\"$(sysconfdir)/nix\" \
  -DNIX_VERSION=\"$(VERSION)\" \
  -I.. ${aterm_include} -I../libutil -I../libstore

src/libmain/shared.cc

@@ -106,6 +106,7 @@ static void initAndRun(int argc, char * * argv)
     nixLogDir = canonPath(getEnv("NIX_LOG_DIR", NIX_LOG_DIR));
     nixStateDir = canonPath(getEnv("NIX_STATE_DIR", NIX_STATE_DIR));
     nixDBPath = getEnv("NIX_DB_DIR", nixStateDir + "/db");
+    nixConfDir = canonPath(getEnv("NIX_CONF_DIR", NIX_CONF_DIR));
 
     /* Check that the store directory and its parent are not
        symlinks. */

src/libstore/gc.cc

@@ -213,14 +213,9 @@ static void readTempRoots(PathSet & tempRoots, FDs & fds)
         lockFile(*fd, ltRead, true);
 
         /* Read the entire file. */
-        struct stat st;
+        string contents = readFile(*fd);
-        if (fstat(*fd, &st) == -1)
-            throw SysError(format("statting `%1%'") % path);
-        unsigned char buf[st.st_size]; /* !!! stack space */
-        readFull(*fd, buf, st.st_size);
 
         /* Extract the roots. */
-        string contents((char *) buf, st.st_size);
         unsigned int pos = 0, end;
 
         while ((end = contents.find((char) 0, pos)) != string::npos) {
@@ -310,7 +305,9 @@ static Paths topoSort(const PathSet & paths)
 void collectGarbage(GCAction action, PathSet & result)
 {
     result.clear();
-    
+
+    string gcKeepOutputs = querySetting("gc-keep-outputs", "false");
+
     /* Acquire the global GC root.  This prevents
        a) New roots from being added.
        b) Processes from creating new temporary root files. */
@@ -333,6 +330,19 @@ void collectGarbage(GCAction action, PathSet & result)
     for (PathSet::const_iterator i = roots.begin(); i != roots.end(); ++i)
         computeFSClosure(canonPath(*i), livePaths);
 
+    if (gcKeepOutputs == "true") {
+        /* Hmz, identical to storePathRequisites in nix-store. */
+        for (PathSet::iterator i = livePaths.begin();
+             i != livePaths.end(); ++i)
+            if (isDerivation(*i)) {
+                Derivation drv = derivationFromPath(*i);
+                for (DerivationOutputs::iterator j = drv.outputs.begin();
+                     j != drv.outputs.end(); ++j)
+                    if (isValidPath(j->second.path))
+                        computeFSClosure(j->second.path, livePaths);
+            }
+    }
+
     if (action == gcReturnLive) {
         result = livePaths;
         return;

src/libstore/globals.cc

@@ -1,10 +1,14 @@
 #include "globals.hh"
 
+#include <map>
+
+
 string nixStore = "/UNINIT";
 string nixDataDir = "/UNINIT";
 string nixLogDir = "/UNINIT";
 string nixStateDir = "/UNINIT";
 string nixDBPath = "/UNINIT";
+string nixConfDir = "/UNINIT";
 
 bool keepFailed = false;
 
@@ -17,3 +21,49 @@ Verbosity buildVerbosity = lvlInfo;
 unsigned int maxBuildJobs = 1;
 
 bool readOnlyMode = false;
+
+
+static bool settingsRead = false;
+
+static map<string, string> settings;
+
+
+static void readSettings()
+{
+    Path settingsFile = (format("%1%/%2%") % nixConfDir % "nix.conf").str();
+    if (!pathExists(settingsFile)) return;
+    string contents = readFile(settingsFile);
+
+    unsigned int pos = 0;
+
+    while (pos < contents.size()) {
+        string line;
+        while (pos < contents.size() && contents[pos] != '\n')
+            line += contents[pos++];
+        pos++;
+
+        unsigned int hash = line.find('#');
+        if (hash != string::npos)
+            line = string(line, 0, hash);
+
+        if (line.find_first_not_of(" ") == string::npos) continue;
+
+        istringstream is(line);
+        string name, sep, value;
+        is >> name >> sep >> value;
+        if (sep != "=" || !is)
+            throw Error(format("illegal configuration line `%1%'") % line);
+        
+        settings[name] = value;
+    };
+    
+    settingsRead = true;
+}
+
+
+string querySetting(const string & name, const string & def)
+{
+    if (!settingsRead) readSettings();
+    map<string, string>::iterator i = settings.find(name);
+    return i == settings.end() ? def : i->second;
+}

src/libstore/globals.hh

@@ -23,6 +23,11 @@ extern string nixStateDir;
 /* nixDBPath is the path name of our Berkeley DB environment. */
 extern string nixDBPath;
 
+/* nixConfDir is the directory where configuration files are
+   stored. */
+extern string nixConfDir;
+
+
 
 /* Misc. global flags. */
 
@@ -48,4 +53,7 @@ extern unsigned int maxBuildJobs;
 extern bool readOnlyMode;
 
 
+string querySetting(const string & name, const string & def);
+
+
 #endif /* !__GLOBALS_H */

src/libutil/util.cc

@@ -164,6 +164,27 @@ Strings readDirectory(const Path & path)
 }
 
 
+string readFile(int fd)
+{
+    struct stat st;
+    if (fstat(fd, &st) == -1)
+        throw SysError("statting file");
+    unsigned char buf[st.st_size]; /* !!! stack space */
+    readFull(fd, buf, st.st_size);
+
+    return string((char *) buf, st.st_size);
+}
+
+
+string readFile(const Path & path)
+{
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1)
+        throw SysError(format("opening file `%1%'") % path);
+    return readFile(fd);
+}
+
+
 static void _deletePath(const Path & path)
 {
     checkInterrupt();

src/libutil/util.hh

@@ -90,6 +90,10 @@ bool isLink(const Path & path);
    removed. */
 Strings readDirectory(const Path & path);
 
+/* Read the contents of a file into a string. */
+string readFile(int fd);
+string readFile(const Path & path);
+
 /* Delete a path; i.e., in the case of a directory, it is deleted
    recursively.  Don't use this at home, kids. */
 void deletePath(const Path & path);