fsmonitor: handle shortname for .git

jeffhostetler · jeffhostetler · commit 4005824c9090 · 2021-08-05T12:14:29.000-04:00
On Windows, teach FSMonitor to recognize the shortname of ".git"
as an alias for ".git".

Sometimes we receive FS events using the shortname, such as when
a CMD shell runs "RENAME GIT~1 FOO" or "RMDIR GIT~1".  The FS
notification arrives using whatever combination of long and
shortnames used by the other process.  (Shortnames do seem to
be case normalized, however.)

NEEDSWORK: This only addresses the case of removing or renaming
the ".git" directory using the shortname alias, so that the daemon
properly shuts down.  I'm leaving it a task for later to handle
the general case of shortnames and report them to the fsmonitor
client process.  This would include tracked and untracked paths
that just happen to have a shortname alias.

Signed-off-by: Jeff Hostetler &lt;jeffhost@microsoft.com&gt;
diff --git a/compat/fsmonitor/fsm-listen-win32.c b/compat/fsmonitor/fsm-listen-win32.c
@@ -48,6 +48,8 @@ struct fsmonitor_daemon_backend_data
 #define LISTENER_HAVE_DATA_WORKTREE 1
 #define LISTENER_HAVE_DATA_GITDIR 2
 	int nr_listener_handles;
+
+	struct strbuf dot_git_shortname;
 };
 
 /*
@@ -258,6 +260,62 @@ static void cancel_rdcw_watch(struct one_watch *watch)
 	watch->is_active = FALSE;
 }
 
+/*
+ * Process a single relative pathname event.
+ * Return 1 if we should shutdown.
+ */
+static int process_1_worktree_event(
+	FILE_NOTIFY_INFORMATION *info,
+	struct string_list *cookie_list,
+	struct fsmonitor_batch **batch,
+	const struct strbuf *path,
+	enum fsmonitor_path_type t)
+{
+	const char *slash;
+
+	switch (t) {
+	case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
+		/* special case cookie files within .git */
+
+		/* Use just the filename of the cookie file. */
+		slash = find_last_dir_sep(path->buf);
+		string_list_append(cookie_list,
+				   slash ? slash + 1 : path->buf);
+		break;
+
+	case IS_INSIDE_DOT_GIT:
+		/* ignore everything inside of "<worktree>/.git/" */
+		break;
+
+	case IS_DOT_GIT:
+		/* "<worktree>/.git" was deleted (or renamed away) */
+		if ((info->Action == FILE_ACTION_REMOVED) ||
+		    (info->Action == FILE_ACTION_RENAMED_OLD_NAME)) {
+			trace2_data_string("fsmonitor", NULL,
+					   "fsm-listen/dotgit",
+					   "removed");
+			return 1;
+		}
+		break;
+
+	case IS_WORKDIR_PATH:
+		/* queue normal pathname */
+		if (!*batch)
+			*batch = fsmonitor_batch__new();
+		fsmonitor_batch__add_path(*batch, path->buf);
+		break;
+
+	case IS_GITDIR:
+	case IS_INSIDE_GITDIR:
+	case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
+	default:
+		BUG("unexpected path classification '%d' for '%s'",
+		    t, path->buf);
+	}
+
+	return 0;
+}
+
 /*
  * Process filesystem events that happen anywhere (recursively) under the
  * <worktree> root directory.  For a normal working directory, this includes
@@ -302,7 +360,6 @@ static int process_worktree_events(struct fsmonitor_daemon_state *state)
 	 */
 	for (;;) {
 		FILE_NOTIFY_INFORMATION *info = (void *)p;
-		const char *slash;
 		enum fsmonitor_path_type t;
 
 		strbuf_reset(&path);
@@ -311,45 +368,45 @@ static int process_worktree_events(struct fsmonitor_daemon_state *state)
 
 		t = fsmonitor_classify_path_workdir_relative(path.buf);
 
-		switch (t) {
-		case IS_INSIDE_DOT_GIT_WITH_COOKIE_PREFIX:
-			/* special case cookie files within .git */
-
-			/* Use just the filename of the cookie file. */
-			slash = find_last_dir_sep(path.buf);
-			string_list_append(&cookie_list,
-					   slash ? slash + 1 : path.buf);
-			break;
-
-		case IS_INSIDE_DOT_GIT:
-			/* ignore everything inside of "<worktree>/.git/" */
-			break;
-
-		case IS_DOT_GIT:
-			/* "<worktree>/.git" was deleted (or renamed away) */
-			if ((info->Action == FILE_ACTION_REMOVED) ||
-			    (info->Action == FILE_ACTION_RENAMED_OLD_NAME)) {
-				trace2_data_string("fsmonitor", NULL,
-						   "fsm-listen/dotgit",
-						   "removed");
-				goto force_shutdown;
-			}
-			break;
-
-		case IS_WORKDIR_PATH:
-			/* queue normal pathname */
-			if (!batch)
-				batch = fsmonitor_batch__new();
-			fsmonitor_batch__add_path(batch, path.buf);
-			break;
-
-		case IS_GITDIR:
-		case IS_INSIDE_GITDIR:
-		case IS_INSIDE_GITDIR_WITH_COOKIE_PREFIX:
-		default:
-			BUG("unexpected path classification '%d' for '%s'",
-			    t, path.buf);
-		}
+		if (process_1_worktree_event(info, &cookie_list, &batch,
+					     &path, t))
+			goto force_shutdown;
+
+		/*
+		 * NEEDSWORK: If `path` contains a shortname (that is,
+		 * if any component within it is a shortname), we
+		 * should expand it to a longname (See
+		 * `GetLongPathNameW()`) and re-normalize, classify,
+		 * and process it because our client is probably
+		 * expecting "normal" paths.
+		 *
+		 * HOWEVER, if our process has called `chdir()` to get
+		 * us out of the root of the worktree (so that the
+		 * root directory is not busy), then we have to be
+		 * careful to convert the paths in the INFO array
+		 * (which are relative to the directory of the RDCW
+		 * watch and not the CWD) into absolute paths before
+		 * calling GetLongPathNameW() and then convert the
+		 * computed value back to a RDCW-relative pathname
+		 * (which is what we and the client expect).
+		 *
+		 * FOR NOW, just handle case (1) exactly so that we
+		 * shutdown properly when ".git" is deleted via the
+		 * shortname alias.
+		 *
+		 * We might see case (2) events for cookie files, but
+		 * we can ignore them.
+		 *
+		 * FOR LATER, handle case (3) where the worktree
+		 * events contain shortnames.  We should convert
+		 * them to longnames to avoid confusing the client.
+		 */
+		if (data->dot_git_shortname.len &&
+		    !strcmp(path.buf, data->dot_git_shortname.buf) &&
+		    process_1_worktree_event(info, &cookie_list, &batch,
+					     &data->dot_git_shortname,
+					     IS_DOT_GIT))
+			goto force_shutdown;
 
 skip_this_path:
 		if (!info->NextEntryOffset)
@@ -423,6 +480,14 @@ static int process_gitdir_events(struct fsmonitor_daemon_state *state)
 			    t, path.buf);
 		}
 
+		/*
+		 * WRT shortnames, this external gitdir will not see
+		 * case (1) nor case (3) events.
+		 *
+		 * We might see case (2) events for cookie files, but
+		 * we can ignore them.
+		 */
+
 skip_this_path:
 		if (!info->NextEntryOffset)
 			break;
@@ -524,6 +589,7 @@ void fsm_listen__loop(struct fsmonitor_daemon_state *state)
 int fsm_listen__ctor(struct fsmonitor_daemon_state *state)
 {
 	struct fsmonitor_daemon_backend_data *data;
+	char shortname[16]; /* a padded 8.3 buffer */
 
 	CALLOC_ARRAY(data, 1);
 
@@ -554,6 +620,52 @@ int fsm_listen__ctor(struct fsmonitor_daemon_state *state)
 		data->nr_listener_handles++;
 	}
 
+	/*
+	 * NEEDSWORK: Properly handle 8.3 shortnames.  RDCW events can
+	 * contain a shortname (if another application uses a
+	 * shortname in a system call).  We care about aliasing and
+	 * the use of shortnames for:
+	 *
+	 * (1) ".git",
+	 *     -- if an external process deletes ".git" using "GIT~1",
+	 *        we need to catch that and shutdown.
+	 *
+	 * (2) our cookie files,
+	 *     -- if an external process deletes one of our cookie
+	 *        files using a shortname, we will get a shortname
+	 *        event for it.  However, we should have already
+	 *        gotten a longname event for it when we created the
+	 *        cookie, so we can safely discard the shortname
+	 *        events for cookie files.
+	 *
+	 * (3) the spelling of modified files that we report to clients.
+	 *     -- we need to report the longname to the client because
+	 *        that is what they are expecting.  Presumably, the
+	 *        client is going to lookup the paths that we report
+	 *        in their index and untracked-cache, so we should
+	 *        normalize the data for them.  (Technically, they
+	 *        could adapt, so we could relax this maybe.)
+	 *
+	 * FOR NOW, while our CWD is at the root of the worktree we
+	 * can easily get the spelling of the shortname of ".git" (if
+	 * the volume has shortnames enabled).  For most worktrees
+	 * this value will be "GIT~1", but we don't want to assume
+	 * that.
+	 *
+	 * Capture this so that we can handle (1).
+	 *
+	 * We leave (3) for a future effort.
+	 */
+	strbuf_init(&data->dot_git_shortname, 0);
+	GetShortPathNameA(".git", shortname, sizeof(shortname));
+	if (!strcmp(".git", shortname))
+		trace_printf_key(&trace_fsmonitor, "No shortname for '.git'");
+	else {
+		trace_printf_key(&trace_fsmonitor,
+				 "Shortname of '.git' is '%s'", shortname);
+		strbuf_addstr(&data->dot_git_shortname, shortname);
+	}
+
 	state->backend_data = data;
 	return 0;
 
diff --git a/t/t7527-builtin-fsmonitor.sh b/t/t7527-builtin-fsmonitor.sh
@@ -123,6 +123,71 @@ test_expect_success 'implicit daemon stop (rename .git)' '
 	test_must_fail git -C test_implicit_2 fsmonitor--daemon status
 '
 
+# File systems on Windows may or may not have shortnames.
+# This is a volume-specific setting on modern systems.
+# "C:/" drives are required to have them enabled.  Other
+# hard drives default to disabled.
+#
+# This is a crude test to see if shortnames are enabled
+# on the volume containing the test directory.  It is
+# crude, but it does not require elevation like `fsutil`.
+#
+test_lazy_prereq SHORTNAMES '
+	mkdir .foo &&
+	test -d "FOO~1"
+'
+
+# Here we assume that the shortname of ".git" is "GIT~1".
+test_expect_success MINGW,SHORTNAMES 'implicit daemon stop (rename GIT~1)' '
+	test_when_finished "stop_daemon_delete_repo test_implicit_1s" &&
+
+	git init test_implicit_1s &&
+
+	start_daemon test_implicit_1s &&
+
+	# renaming the .git directory will implicitly stop the daemon.
+	# this moves {.git, GIT~1} to {.gitxyz, GITXYZ~1}.
+	# the rename-from FS Event will contain the shortname.
+	#
+	mv test_implicit_1s/GIT~1 test_implicit_1s/.gitxyz &&
+
+	sleep 1 &&
+	# put it back so that our status will not crawl out to our
+	# parent directory.
+	# this moves {.gitxyz, GITXYZ~1} to {.git, GIT~1}.
+	mv test_implicit_1s/.gitxyz test_implicit_1s/.git &&
+
+	test_must_fail git -C test_implicit_1s fsmonitor--daemon status
+'
+
+# Here we first create a file with LONGNAME of "GIT~1" before
+# we create the repo.  This will cause the shortname of ".git"
+# to be "GIT~2".
+test_expect_success MINGW,SHORTNAMES 'implicit daemon stop (rename GIT~2)' '
+	test_when_finished "stop_daemon_delete_repo test_implicit_1s2" &&
+
+	mkdir test_implicit_1s2 &&
+	echo HELLO >test_implicit_1s2/GIT~1 &&
+	git init test_implicit_1s2 &&
+
+	test_path_is_file test_implicit_1s2/GIT~1 &&
+	test_path_is_dir  test_implicit_1s2/GIT~2 &&
+
+	start_daemon test_implicit_1s2 &&
+
+	# renaming the .git directory will implicitly stop the daemon.
+	# the rename-from FS Event will contain the shortname.
+	#
+	mv test_implicit_1s2/GIT~2 test_implicit_1s2/.gitxyz &&
+
+	sleep 1 &&
+	# put it back so that our status will not crawl out to our
+	# parent directory.
+	mv test_implicit_1s2/.gitxyz test_implicit_1s2/.git &&
+
+	test_must_fail git -C test_implicit_1s2 fsmonitor--daemon status
+'
+
 test_expect_success 'cannot start multiple daemons' '
 	test_when_finished "stop_daemon_delete_repo test_multiple" &&
 
