std.fs.Dir.makeOpenPath: optimize case, if path already exists

Uses a single NtCreateFile syscall on windows. Closes ziglang#12474. Thanks to @joedavis for the PR.
matu3ba · Dec 8, 2022 · 7b6da7c · 7b6da7c
1 parent 225ed65
commit 7b6da7c
Showing 1 changed file with 52 additions and 12 deletions.
diff --git a/lib/std/fs.zig b/lib/std/fs.zig
@@ -1464,19 +1464,51 @@ pub const Dir = struct {
     /// This function performs `makePath`, followed by `openDir`.
     /// If supported by the OS, this operation is atomic. It is not atomic on
     /// all operating systems.
-    pub fn makeOpenPath(self: Dir, sub_path: []const u8, open_dir_options: OpenDirOptions) !Dir {
-        // TODO improve this implementation on Windows; we can avoid 1 call to NtClose
-        try self.makePath(sub_path);
-        return self.openDir(sub_path, open_dir_options);
+    pub fn makeOpenPath(self: Dir, sub_path: []const u8, open_dir_options: OpenDirOptions) error{FileNotFound}!Dir {
+        if (builtin.os.tag == .windows) {
+            const w = os.windows;
+            const sub_path_w = try w.sliceToPrefixedFileW(sub_path);
+
+            const base_flags = w.STANDARD_RIGHTS_READ | w.FILE_READ_ATTRIBUTES | w.FILE_READ_EA |
+                w.SYNCHRONIZE | w.FILE_TRAVERSE;
+            return self.openDirAccessMaskW(sub_path_w.span().ptr, base_flags, .{
+                .no_follow = open_dir_options.no_follow,
+                .create = true,
+            });
+        }
+
+        if (self.openDir(sub_path, open_dir_options)) |dir| {
+            return dir;
+        } else |_| {
+            try self.makePath(sub_path);
+            return self.openDir(sub_path, open_dir_options) catch return error.FileNotFound;
+        }
     }
 
     /// This function performs `makePath`, followed by `openIterableDir`.
     /// If supported by the OS, this operation is atomic. It is not atomic on
     /// all operating systems.
     pub fn makeOpenPathIterable(self: Dir, sub_path: []const u8, open_dir_options: OpenDirOptions) !IterableDir {
-        // TODO improve this implementation on Windows; we can avoid 1 call to NtClose
-        try self.makePath(sub_path);
-        return self.openIterableDir(sub_path, open_dir_options);
+        if (builtin.os.tag == .windows) {
+            const w = os.windows;
+            const sub_path_w = try w.sliceToPrefixedFileW(sub_path);
+
+            const base_flags = w.STANDARD_RIGHTS_READ | w.FILE_READ_ATTRIBUTES | w.FILE_READ_EA |
+                w.SYNCHRONIZE | w.FILE_TRAVERSE | w.FILE_LIST_DIRECTORY;
+            return IterableDir{
+                .dir = try self.openDirAccessMaskW(sub_path_w.span().ptr, base_flags, .{
+                    .no_follow = open_dir_options.no_follow,
+                    .create = true,
+                }),
+            };
+        }
+
+        if (self.openIterableDir(sub_path, open_dir_options)) |dir| {
+            return dir;
+        } else |_| {
+            try self.makePath(sub_path);
+            return self.openIterableDir(sub_path, open_dir_options) catch return error.FileNotFound;
+        }
     }
 
     ///  This function returns the canonicalized absolute pathname of
@@ -1730,7 +1762,10 @@ pub const Dir = struct {
         const base_flags = w.STANDARD_RIGHTS_READ | w.FILE_READ_ATTRIBUTES | w.FILE_READ_EA |
             w.SYNCHRONIZE | w.FILE_TRAVERSE;
         const flags: u32 = if (iterable) base_flags | w.FILE_LIST_DIRECTORY else base_flags;
-        var dir = try self.openDirAccessMaskW(sub_path_w, flags, args.no_follow);
+        var dir = try self.openDirAccessMaskW(sub_path_w, flags, .{
+            .no_follow = args.no_follow,
+            .create = false,
+        });
         return dir;
     }
 
@@ -1753,7 +1788,12 @@ pub const Dir = struct {
         return Dir{ .fd = fd };
     }
 
-    fn openDirAccessMaskW(self: Dir, sub_path_w: [*:0]const u16, access_mask: u32, no_follow: bool) OpenError!Dir {
+    const OpenDirAccessMaskWOptions = struct {
+        no_follow: bool,
+        create: bool,
+    };
+
+    fn openDirAccessMaskW(self: Dir, sub_path_w: [*:0]const u16, access_mask: u32, flags: OpenDirAccessMaskWOptions) OpenError!Dir {
         const w = os.windows;
 
         var result = Dir{
@@ -1774,17 +1814,17 @@ pub const Dir = struct {
             .SecurityDescriptor = null,
             .SecurityQualityOfService = null,
         };
-        const open_reparse_point: w.DWORD = if (no_follow) w.FILE_OPEN_REPARSE_POINT else 0x0;
+        const open_reparse_point: w.DWORD = if (flags.no_follow) w.FILE_OPEN_REPARSE_POINT else 0x0;
         var io: w.IO_STATUS_BLOCK = undefined;
         const rc = w.ntdll.NtCreateFile(
             &result.fd,
             access_mask,
             &attr,
             &io,
             null,
-            0,
+            w.FILE_ATTRIBUTE_NORMAL,
             w.FILE_SHARE_READ | w.FILE_SHARE_WRITE,
-            w.FILE_OPEN,
+            if (flags.create) w.FILE_OPEN_IF else w.FILE_OPEN,
             w.FILE_DIRECTORY_FILE | w.FILE_SYNCHRONOUS_IO_NONALERT | w.FILE_OPEN_FOR_BACKUP_INTENT | open_reparse_point,
             null,
             0,