libstore: simplify makeTemp{,Sibling}Path callers

There is now no risk of race conditions on a system with a functioning
entropy source, and the bespoke prefixes are either redundant to the
default or unnecessary.

Change-Id: I6a6a69648a3b8060333e97269ea8b72499614559

lix/libstore/build/derivation-goal.cc

@@ -761,11 +761,7 @@ void replaceValidPath(const Path & storePath, const Path & tmpPath)
        we're repairing (say) Glibc, we end up with a broken system. */
     Path oldPath;
     if (pathExists(storePath)) {
-        do {
-            oldPath = makeTempSiblingPath(storePath);
-            // store paths are often directories so we can't just unlink() it
-            // let's make sure the path doesn't exist before we try to use it
-        } while (pathExists(oldPath));
+        oldPath = makeTempSiblingPath(storePath);
         movePath(storePath, oldPath);
     }
 

lix/libstore/gc.cc

@@ -42,7 +42,6 @@ static void makeSymlink(const Path & link, const Path & target)
 
     /* Create the new symlink. */
     Path tempLink = makeTempPath(link);
-    unlink(tempLink.c_str()); // just in case; ignore errors
     createSymlink(target, tempLink);
 
     /* Atomically replace the old one. */
@@ -97,7 +96,7 @@ void LocalStore::createTempRootsFile()
 
     /* Create the temporary roots file for this process. */
     while (true) {
-        auto tmp = makeTempPath(fnTempRoots, ".tmp");
+        auto tmp = makeTempPath(fnTempRoots);
         AutoCloseFD fd{open(tmp.c_str(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600)};
         if (!fd && errno != EEXIST) {
             throw SysError("opening lock file '%1%'", tmp);

lix/libstore/optimise-store.cc

@@ -218,8 +218,7 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
        its timestamp back to 0. */
     MakeReadOnly makeReadOnly(mustToggle ? dirOfPath : "");
 
-    Path tempLink = makeTempPath(config().realStoreDir, "/.tmp-link");
-    unlink(tempLink.c_str()); // just in case; ignore errors
+    Path tempLink = makeTempPath(config().realStoreDir + "/");
 
     if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
         if (errno == EMLINK) {