guix-register: Add '--state-directory' parameter.

* nix/guix-register/guix-register.cc (GUIX_OPT_STATE_DIRECTORY): New
  macro.
  (parse_opt): Honor it.
* tests/guix-register.sh: Add test with '--state-directory'.
* guix/store.scm (register-path): Add #:state-directory parameter.

guix/store.scm

@@ -797,11 +797,14 @@ (define ordered
               (loop tail)))))))
 
 (define* (register-path path
-                        #:key (references '()) deriver prefix)
+                        #:key (references '()) deriver prefix
+                        state-directory)
   "Register PATH as a valid store file, with REFERENCES as its list of
 references, and DERIVER as its deriver (.drv that led to it.)  If PREFIX is
 not #f, it must be the name of the directory containing the new store to
-initialize.  Return #t on success.
+initialize; if STATE-DIRECTORY is not #f, it must be a string containing the
+absolute file name to the state directory of the store being initialized.
+Return #t on success.
 
 Use with care as it directly modifies the store!  This is primarily meant to
 be used internally by the daemon's build hook."
@@ -809,9 +812,12 @@ (define* (register-path path
   (catch 'system-error
     (lambda ()
       (let ((pipe (apply open-pipe* OPEN_WRITE %guix-register-program
-                         (if prefix
+                         `(,@(if prefix
                                  `("--prefix" ,prefix)
-                             '()))))
+                                 '())
+                           ,@(if state-directory
+                                 `("--state-directory" ,state-directory)
+                                 '())))))
         (and pipe
              (begin
                (format pipe "~a~%~a~%~a~%"

nix/guix-register/guix-register.cc

@@ -56,10 +56,14 @@ from an existing store.  It updates the new store's database with \
 information about which store files are valid, and what their \
 references are.";
 
+#define GUIX_OPT_STATE_DIRECTORY 1
+
 static const struct argp_option options[] =
   {
     { "prefix", 'p', "DIRECTORY", 0,
       "Open the store that lies under DIRECTORY" },
+    { "state-directory", GUIX_OPT_STATE_DIRECTORY, "DIRECTORY", 0,
+      "Use DIRECTORY as the state directory of the target store" },
     { 0, 0, 0, 0, 0 }
   };
 
@@ -84,6 +88,15 @@ parse_opt (int key, char *arg, struct argp_state *state)
 	break;
       }
 
+    case GUIX_OPT_STATE_DIRECTORY:
+      {
+	string state_dir = canonPath (arg);
+
+	settings.nixStateDir = state_dir;
+	settings.nixDBPath = state_dir + "/db";
+	break;
+      }
+
     case ARGP_KEY_ARG:
       {
 	std::ifstream *file;

tests/guix-register.sh

@@ -79,12 +79,19 @@ guix-register -p "$new_store" < "$closure"
 # Doing it a second time shouldn't hurt.
 guix-register --prefix "$new_store" "$closure"
 
+# Same, but with the database stored in a different place.
+guix-register -p "$new_store" \
+    --state-directory "$new_store/chbouib" "$closure"
+
 # Now make sure this is recognized as valid.
 
+ls -R "$new_store"
+for state_dir in "$new_store$localstatedir/guix" "$new_store/chbouib"
+do
     NIX_STORE_DIR="$new_store_dir"
-NIX_STATE_DIR="$new_store$localstatedir"
+    NIX_STATE_DIR="$new_store$state_dir"
-NIX_LOG_DIR="$new_store$localstatedir/log/guix"
+    NIX_LOG_DIR="$new_store$state_dir/log/guix"
-NIX_DB_DIR="$new_store$localstatedir/guix/db"
+    NIX_DB_DIR="$new_store$state_dir/db"
 
     export NIX_IGNORE_SYMLINK_STORE NIX_STORE_DIR NIX_STATE_DIR	\
 	NIX_LOG_DIR NIX_DB_DIR
@@ -96,7 +103,7 @@ exit_hook="kill $subdaemon_pid"
     final_name="$storedir/`basename $to_copy`"
 
     # At this point the copy in $new_store must be valid, and unreferenced.
-# The database under $new_store uses the $final_name, but we can't use
+    # The database under $NIX_DB_DIR uses the $final_name, but we can't use
     # that name in a 'valid-path?' query because 'assertStorePath' would kill
     # us because of the wrong prefix.  So we just list dead paths instead.
     guile -c "
@@ -104,9 +111,16 @@ guile -c "
       (define s (open-connection))
       (exit (equal? (list \"$copied\") (dead-paths s)))"
 
+    # Kill the daemon so we can access the database below (otherwise we may
+    # get "database is locked" errors.)
+    kill $subdaemon_pid
+    exit_hook=":"
+    while kill -0 $subdaemon_pid ; do sleep 0.5 ; done
+
     # When 'sqlite3' is available, check the name in the database.
     if type -P sqlite3
     then
 	echo "select * from ValidPaths where path=\"$final_name\";" | \
-	sqlite3 $NIX_DB_DIR/db.sqlite
+	    sqlite3 "$NIX_DB_DIR/db.sqlite"
     fi
+done