* The environment variable NIX_ROOT can now be set to execute Nix in a

chroot() environment.
* A operation `--validpath' to register path validity.  Useful for
  bootstrapping in a pure Nix environment.
* Safety checks: ensure that files involved in store operations are in
  the store.

src/libmain/shared.cc

@@ -22,6 +22,13 @@ void sigintHandler(int signo)
    processor. */
 static void initAndRun(int argc, char * * argv)
 {
+    char * root = getenv("NIX_ROOT");
+
+    if (root) {
+        if (chroot(root) != 0)
+            throw SysError(format("changing root to `%1%'") % root);
+    }
+    
     /* Setup Nix paths. */
     nixStore = NIX_STORE_DIR;
     nixDataDir = NIX_DATA_DIR;

src/libstore/store.cc

@@ -157,6 +157,22 @@ void copyPath(const Path & src, const Path & dst)
 }
 
 
+static bool isInStore(const Path & path)
+{
+    return path[0] == '/'
+        && Path(path, 0, nixStore.size()) == nixStore
+        && path.size() > nixStore.size() + 1
+        && path[nixStore.size()] == '/';
+}
+
+
+static void assertStorePath(const Path & path)
+{
+    if (!isInStore(path))
+        throw Error(format("path `%1%' is not in the Nix store") % path);
+}
+
+
 static bool isValidPathTxn(const Path & path, const Transaction & txn)
 {
     string s;
@@ -182,6 +198,9 @@ static bool isUsablePathTxn(const Path & path, const Transaction & txn)
 void registerSuccessor(const Transaction & txn,
     const Path & srcPath, const Path & sucPath)
 {
+    assertStorePath(srcPath);
+    assertStorePath(sucPath);
+    
     if (!isUsablePathTxn(sucPath, txn))	throw Error(
 	format("path `%1%' cannot be a successor, since it is not usable")
 	% sucPath);
@@ -223,6 +242,9 @@ Paths queryPredecessors(const Path & sucPath)
 
 void registerSubstitute(const Path & srcPath, const Path & subPath)
 {
+    assertStorePath(srcPath);
+    assertStorePath(subPath);
+    
     if (!isValidPathTxn(subPath, noTxn)) throw Error(
 	format("path `%1%' cannot be a substitute, since it is not valid")
 	% subPath);
@@ -262,6 +284,7 @@ Paths querySubstitutes(const Path & srcPath)
 void registerValidPath(const Transaction & txn, const Path & _path)
 {
     Path path(canonPath(_path));
+    assertStorePath(path);
     debug(format("registering path `%1%'") % path);
     nixDB.setString(txn, dbValidPaths, path, "");
 }
@@ -312,13 +335,6 @@ static void invalidatePath(const Path & path, Transaction & txn)
 }
 
 
-static bool isInPrefix(const string & path, const string & _prefix)
-{
-    string prefix = canonPath(_prefix + "/");
-    return string(path, 0, prefix.size()) == prefix;
-}
-
-
 Path addToStore(const Path & _srcPath)
 {
     Path srcPath(absPath(_srcPath));
@@ -355,6 +371,8 @@ Path addToStore(const Path & _srcPath)
 
 void addTextToStore(const Path & dstPath, const string & s)
 {
+    assertStorePath(dstPath);
+    
     if (!isValidPath(dstPath)) {
 
         PathSet lockPaths;
@@ -378,8 +396,7 @@ void deleteFromStore(const Path & _path)
 {
     Path path(canonPath(_path));
 
-    if (!isInPrefix(path, nixStore))
-        throw Error(format("path `%1%' is not in the store") % path);
+    assertStorePath(path);
 
     Transaction txn(nixDB);
     invalidatePath(path, txn);
@@ -402,6 +419,9 @@ void verifyStore()
         if (!pathExists(path)) {
             printMsg(lvlError, format("path `%1%' disappeared") % path);
             invalidatePath(path, txn);
+        } else if (!isInStore(path)) {
+            printMsg(lvlError, format("path `%1%' is not in the Nix store") % path);
+            invalidatePath(path, txn);
         } else
             validPaths.insert(path);
     }

src/nix-store/help.txt

@@ -9,8 +9,10 @@ Operations:
   --add / -A: copy a path to the Nix store
   --query / -q: query information
 
-  --successor: register a successor expression
-  --substitute: register a substitute expression
+  --successor: register a successor expression (dangerous!)
+  --substitute: register a substitute expression (dangerous!)
+  --validpath: register path validity (dangerous!)
+  --isvalid: check path validity
 
   --dump: dump a path as a Nix archive
   --restore: restore a path from a Nix archive

src/nix-store/main.cc

@@ -185,6 +185,30 @@ static void opSubstitute(Strings opFlags, Strings opArgs)
 }
 
 
+static void opValidPath(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    
+    Transaction txn;
+    createStoreTransaction(txn);
+    for (Strings::iterator i = opArgs.begin();
+         i != opArgs.end(); ++i)
+        registerValidPath(txn, *i);
+    txn.commit();
+}
+
+
+static void opIsValid(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+
+    for (Strings::iterator i = opArgs.begin();
+         i != opArgs.end(); ++i)
+        if (!isValidPath(*i))
+            throw Error(format("path `%1%' is not valid") % *i);
+}
+
+
 /* A sink that writes dump output to stdout. */
 struct StdoutSink : DumpSink
 {
@@ -273,6 +297,10 @@ void run(Strings args)
             op = opSuccessor;
         else if (arg == "--substitute")
             op = opSubstitute;
+        else if (arg == "--validpath")
+            op = opValidPath;
+        else if (arg == "--isvalid")
+            op = opIsValid;
         else if (arg == "--dump")
             op = opDump;
         else if (arg == "--restore")
@@ -292,7 +320,8 @@ void run(Strings args)
 
     if (!op) throw UsageError("no operation specified");
 
-    openDB();
+    if (op != opDump && op != opRestore) /* !!! hack */
+        openDB();
 
     op(opFlags, opArgs);
 }