WIP: restore /nix/var/nix as source of truth for profiles

See-also: https://github.com/NixOS/nix/pull/5226
Change-Id: I35082c9a59148f7fb132232659c3a254d514d190

src/libcmd/command.cc

@@ -269,7 +269,15 @@ void MixProfile::updateProfile(const BuiltPaths & buildables)
 
 MixDefaultProfile::MixDefaultProfile()
 {
-    profile = getDefaultProfile();
+    static bool haveWarned = false;
+    try {
+        // `nix profile remove` at the least seems to expect this.
+        this->profile = ensureDefaultProfile();
+    } catch (SysError const & e) {
+        // However we get called in __dumpCli too, so we should not do fatal IO.
+        warnOnce(haveWarned, "ignoring error initializing default profile %s", e.what());
+        this->profile = getDefaultProfile();
+    }
 }
 
 MixEnvironment::MixEnvironment() : ignoreEnvironment(false)

src/libstore/local-store.cc

@@ -216,6 +216,10 @@ LocalStore::LocalStore(const Params & params)
         }
     }
 
+    if (!readOnly) {
+        createUser(getUserName(), getuid());
+    }
+
     /* Optionally, create directories and set permissions for a
        multi-user install. */
     if (getuid() == 0 && settings.buildUsersGroup != "") {
@@ -1788,6 +1792,27 @@ void LocalStore::signRealisation(Realisation & realisation)
     }
 }
 
+void LocalStore::createUser(std::string_view userName, uid_t userId)
+{
+    using namespace std::literals::string_view_literals;
+
+    // FIXME(Qyriad): is /nix/var/nix/gcroots/per-user used anywhere...?
+    for (auto const & dirPart : {"profiles"sv, "gcroots"sv}) {
+
+        auto const fullPerUserDir = fmt("%s/%s/per-user/%s", stateDir, dirPart, userName);
+        createDirs(fullPerUserDir);
+
+        if (chmod(fullPerUserDir.c_str(), 0755) == -1) {
+            throw SysError(errno, "changing permissions of directory '%s'", fullPerUserDir);
+        }
+
+        if (chown(fullPerUserDir.c_str(), userId, getgid()) == -1) {
+            throw SysError(errno, "changing owner of directory '%s'", fullPerUserDir);
+        }
+    }
+
+}
+
 void LocalStore::signPathInfo(ValidPathInfo & info)
 {
     // FIXME: keep secret keys in memory.

src/libstore/local-store.hh

@@ -364,6 +364,8 @@ private:
     void signPathInfo(ValidPathInfo & info);
     void signRealisation(Realisation &);
 
+    void createUser(std::string_view userName, uid_t userId) override;
+
     // XXX: Make a generic `Store` method
     ContentAddress hashCAPath(
         const ContentAddressMethod & method,

src/libstore/profiles.cc

@@ -307,12 +307,7 @@ std::string optimisticLockProfile(const Path & profile)
 
 Path profilesDir()
 {
-    auto profileRoot =
-        (getuid() == 0)
-        ? rootProfilesDir()
-        : createNixStateDir() + "/profiles";
-    createDirs(profileRoot);
-    return profileRoot;
+    return fmt("%s/profiles/per-user/%s", settings.nixStateDir, getUserName());
 }
 
 Path rootProfilesDir()
@@ -332,24 +327,40 @@ Path getDefaultProfileLink()
     return getHome() + "/.nix-profile";
 }
 
+Path ensureDefaultProfile()
+{
+    Path const profileLink = getDefaultProfileLink();
+    Path const defaultProfile = profilesDir() + "/profile";
+
+    if (!pathExists(profileLink)) {
+        replaceSymlink(defaultProfile, profileLink);
+    }
+
+    // Backwards compatibiliy measure: Make root's profile available as
+    // `.../default` as it's what NixOS and most of the init scripts expect
+    Path const globalProfileLink = settings.nixStateDir + "/profiles/default";
+    if (getuid() == 0 && !pathExists(globalProfileLink)) {
+        replaceSymlink(defaultProfile, globalProfileLink);
+    }
+
+    return absPath(readLink(profileLink), dirOf(profileLink));
+}
+
 Path getDefaultProfile()
 {
-    Path profileLink = settings.useXDGBaseDirectories ? createNixStateDir() + "/profile" : getHome() + "/.nix-profile";
+    Path const profileLink = getDefaultProfileLink();
+
     try {
-        auto profile = profilesDir() + "/profile";
-        if (!pathExists(profileLink)) {
-            replaceSymlink(profile, profileLink);
+        if (pathExists(profileLink)) {
+            return absPath(readLink(profileLink), dirOf(profileLink));
         }
-        // Backwards compatibiliy measure: Make root's profile available as
-        // `.../default` as it's what NixOS and most of the init scripts expect
-        Path globalProfileLink = settings.nixStateDir + "/profiles/default";
-        if (getuid() == 0 && !pathExists(globalProfileLink)) {
-            replaceSymlink(profile, globalProfileLink);
-        }
-        return absPath(readLink(profileLink), dirOf(profileLink));
-    } catch (Error &) {
-        return profileLink;
+    } catch (SysError const & e) {
+        printInfo("ignoring error resolving default profile '%s': %s", profileLink, e.what());
+    } catch (Error const & e) {
+        printError("ignoring error resolving default profile '%s': %s", profileLink, e.what());
     }
+
+    return profileLink;
 }
 
 Path defaultChannelsDir()

src/libstore/profiles.hh

@@ -235,9 +235,14 @@ Path getDefaultProfileLink();
 
 /**
  * Resolve the default profile (~/.nix-profile by default,
- * $XDG_STATE_HOME/nix/profile if XDG Base Directory Support is enabled),
- * and create if doesn't exist
+ * $XDG_STATE_HOME/nix/profile if XDG Base Directory Support is enabled).
  */
 Path getDefaultProfile();
 
+/**
+ * Resolve the default profile (see getDefaultProfile()),
+ * and create it if it doesn't exist.
+ */
+Path ensureDefaultProfile();
+
 }

src/libstore/store-api.hh

@@ -845,6 +845,11 @@ public:
         return toRealPath(printStorePath(storePath));
     }
 
+    virtual void createUser(std::string_view userName, uid_t userId)
+    {
+        warn("base class Store called unimplemented createUser()");
+    }
+
     /**
      * Synchronises the options of the client with those of the daemon
      * (a no-op when there’s no daemon)

src/nix-env/nix-env.cc

@@ -1532,7 +1532,7 @@ static int main_nix_env(int argc, char * * argv)
             globals.profile = getEnv("NIX_PROFILE").value_or("");
 
         if (globals.profile == "") {
-            globals.profile = getDefaultProfile();
+            globals.profile = ensureDefaultProfile();
         }
 
         op(globals, std::move(opFlags), std::move(opArgs));

src/nix/daemon.cc

@@ -357,6 +357,13 @@ static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
                 //  Restore normal handling of SIGCHLD.
                 setSigChldAction(false);
 
+                auto store = openUncachedStore();
+                try {
+                    store->createUser(user, peer.uid);
+                } catch (SysError const & e) {
+                    printError("ignoring error while creating store per-user state: %s", e.what());
+                }
+
                 //  For debugging, stuff the pid into argv[1].
                 if (peer.pidKnown && savedArgv[1]) {
                     auto processName = std::to_string(peer.pid);
@@ -366,7 +373,7 @@ static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
                 //  Handle the connection.
                 FdSource from(remote.get());
                 FdSink to(remote.get());
-                processConnection(openUncachedStore(), from, to, trusted, NotRecursive);
+                processConnection(store, from, to, trusted, NotRecursive);
 
                 exit(0);
             }, options);

tests/functional/common/vars-and-functions.sh.in

@@ -66,7 +66,7 @@ readLink() {
 }
 
 clearProfiles() {
-    profiles="$HOME"/.local/state/nix/profiles
+	profiles="$NIX_STATE_DIR/profiles/per-user/$(whoami || echo -n nixbld)"
     rm -rf "$profiles"
 }