internal/syscall/windows: add Openat, Mkdirat

Windows versions of openat and mkdirat,
implemented using NtCreateFile.

For #67002

Change-Id: If43b1c1069733e5c45f7d45a69699fec30187308
Reviewed-on: https://go-review.googlesource.com/c/go/+/619435
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

4 files changed, 213 insertions, 13 deletions

diff --git a/src/internal/syscall/windows/at_windows.go b/src/internal/syscall/windows/at_windows.go
new file mode 100644
index 0000000000..17a8c592f9
--- /dev/null
+++ b/src/internal/syscall/windows/at_windows.go
@@ -0,0 +1,168 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package windows
+
+import (
+	"syscall"
+)
+
+// Openat flags not supported by syscall.Open.
+//
+// These are invented values.
+//
+// When adding a new flag here, add an unexported version to
+// the set of invented O_ values in syscall/types_windows.go
+// to avoid overlap.
+const (
+	O_DIRECTORY    = 0x100000   // target must be a directory
+	O_NOFOLLOW_ANY = 0x20000000 // disallow symlinks anywhere in the path
+)
+
+func Openat(dirfd syscall.Handle, name string, flag int, perm uint32) (_ syscall.Handle, e1 error) {
+	if len(name) == 0 {
+		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
+	}
+
+	var access, options uint32
+	switch flag & (syscall.O_RDONLY | syscall.O_WRONLY | syscall.O_RDWR) {
+	case syscall.O_RDONLY:
+		// FILE_GENERIC_READ includes FILE_LIST_DIRECTORY.
+		access = FILE_GENERIC_READ
+	case syscall.O_WRONLY:
+		access = FILE_GENERIC_WRITE
+		options |= FILE_NON_DIRECTORY_FILE
+	case syscall.O_RDWR:
+		access = FILE_GENERIC_READ | FILE_GENERIC_WRITE
+		options |= FILE_NON_DIRECTORY_FILE
+	}
+	if flag&syscall.O_CREAT != 0 {
+		access |= FILE_GENERIC_WRITE
+	}
+	if flag&syscall.O_APPEND != 0 {
+		access &^= FILE_WRITE_DATA
+		access |= FILE_APPEND_DATA
+	}
+	if flag&O_DIRECTORY != 0 {
+		options |= FILE_DIRECTORY_FILE
+		access |= FILE_LIST_DIRECTORY
+	}
+	if flag&syscall.O_SYNC != 0 {
+		options |= FILE_WRITE_THROUGH
+	}
+	// Allow File.Stat.
+	access |= STANDARD_RIGHTS_READ | FILE_READ_ATTRIBUTES | FILE_READ_EA
+
+	objAttrs := &OBJECT_ATTRIBUTES{}
+	if flag&O_NOFOLLOW_ANY != 0 {
+		objAttrs.Attributes |= OBJ_DONT_REPARSE
+	}
+	if flag&syscall.O_CLOEXEC == 0 {
+		objAttrs.Attributes |= OBJ_INHERIT
+	}
+	if err := objAttrs.init(dirfd, name); err != nil {
+		return syscall.InvalidHandle, err
+	}
+
+	// We don't use FILE_OVERWRITE/FILE_OVERWRITE_IF, because when opening
+	// a file with FILE_ATTRIBUTE_READONLY these will replace an existing
+	// file with a new, read-only one.
+	//
+	// Instead, we ftruncate the file after opening when O_TRUNC is set.
+	var disposition uint32
+	switch {
+	case flag&(syscall.O_CREAT|syscall.O_EXCL) == (syscall.O_CREAT | syscall.O_EXCL):
+		disposition = FILE_CREATE
+	case flag&syscall.O_CREAT == syscall.O_CREAT:
+		disposition = FILE_OPEN_IF
+	default:
+		disposition = FILE_OPEN
+	}
+
+	fileAttrs := uint32(FILE_ATTRIBUTE_NORMAL)
+	if perm&syscall.S_IWRITE == 0 {
+		fileAttrs = FILE_ATTRIBUTE_READONLY
+	}
+
+	var h syscall.Handle
+	err := NtCreateFile(
+		&h,
+		SYNCHRONIZE|access,
+		objAttrs,
+		&IO_STATUS_BLOCK{},
+		nil,
+		fileAttrs,
+		FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
+		disposition,
+		FILE_SYNCHRONOUS_IO_NONALERT|options,
+		0,
+		0,
+	)
+	if err != nil {
+		return h, ntCreateFileError(err, flag)
+	}
+
+	if flag&syscall.O_TRUNC != 0 {
+		err = syscall.Ftruncate(h, 0)
+		if err != nil {
+			syscall.CloseHandle(h)
+			return syscall.InvalidHandle, err
+		}
+	}
+
+	return h, nil
+}
+
+// ntCreateFileError maps error returns from NTCreateFile to user-visible errors.
+func ntCreateFileError(err error, flag int) error {
+	s, ok := err.(NTStatus)
+	if !ok {
+		// Shouldn't really be possible, NtCreateFile always returns NTStatus.
+		return err
+	}
+	switch s {
+	case STATUS_REPARSE_POINT_ENCOUNTERED:
+		return syscall.ELOOP
+	case STATUS_NOT_A_DIRECTORY:
+		// ENOTDIR is the errno returned by open when O_DIRECTORY is specified
+		// and the target is not a directory.
+		//
+		// NtCreateFile can return STATUS_NOT_A_DIRECTORY under other circumstances,
+		// such as when opening "file/" where "file" is not a directory.
+		// (This might be Windows version dependent.)
+		//
+		// Only map STATUS_NOT_A_DIRECTORY to ENOTDIR when O_DIRECTORY is specified.
+		if flag&O_DIRECTORY != 0 {
+			return syscall.ENOTDIR
+		}
+	case STATUS_FILE_IS_A_DIRECTORY:
+		return syscall.EISDIR
+	}
+	return s.Errno()
+}
+
+func Mkdirat(dirfd syscall.Handle, name string, mode uint32) error {
+	objAttrs := &OBJECT_ATTRIBUTES{}
+	if err := objAttrs.init(dirfd, name); err != nil {
+		return err
+	}
+	var h syscall.Handle
+	err := NtCreateFile(
+		&h,
+		FILE_GENERIC_READ,
+		objAttrs,
+		&IO_STATUS_BLOCK{},
+		nil,
+		syscall.FILE_ATTRIBUTE_NORMAL,
+		syscall.FILE_SHARE_READ|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_DELETE,
+		FILE_CREATE,
+		FILE_DIRECTORY_FILE,
+		0,
+		0,
+	)
+	if err != nil {
+		return ntCreateFileError(err, 0)
+	}
+	return nil
+}
diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index 2849376dd1..924f4951e7 100644
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -517,6 +517,16 @@ func (s NTStatus) Error() string {
 	return s.Errno().Error()
 }
 
+// x/sys/windows/mkerrors.bash can generate a complete list of NTStatus codes.
+//
+// At the moment, we only need a couple, so just put them here manually.
+// If this list starts getting long, we should consider generating the full set.
+const (
+	STATUS_FILE_IS_A_DIRECTORY       NTStatus = 0xC00000BA
+	STATUS_NOT_A_DIRECTORY           NTStatus = 0xC0000103
+	STATUS_REPARSE_POINT_ENCOUNTERED NTStatus = 0xC000050B
+)
+
 // NT Native APIs
 //sys   NtCreateFile(handle *syscall.Handle, access uint32, oa *OBJECT_ATTRIBUTES, iosb *IO_STATUS_BLOCK, allocationSize *int64, attributes uint32, share uint32, disposition uint32, options uint32, eabuffer uintptr, ealength uint32) (ntstatus error) = ntdll.NtCreateFile
 //sys   rtlNtStatusToDosErrorNoTeb(ntstatus NTStatus) (ret syscall.Errno) = ntdll.RtlNtStatusToDosErrorNoTeb
diff --git a/src/internal/syscall/windows/types_windows.go b/src/internal/syscall/windows/types_windows.go
index 0421c3a35a..514feafae4 100644
--- a/src/internal/syscall/windows/types_windows.go
+++ b/src/internal/syscall/windows/types_windows.go
@@ -4,7 +4,10 @@
 
 package windows
 
-import "syscall"
+import (
+	"syscall"
+	"unsafe"
+)
 
 // Socket related.
 const (
@@ -105,6 +108,23 @@ type OBJECT_ATTRIBUTES struct {
 	SecurityQoS        *SECURITY_QUALITY_OF_SERVICE
 }
 
+// init sets o's RootDirectory, ObjectName, and Length.
+func (o *OBJECT_ATTRIBUTES) init(root syscall.Handle, name string) error {
+	if name == "." {
+		name = ""
+	}
+	objectName, err := NewNTUnicodeString(name)
+	if err != nil {
+		return err
+	}
+	o.ObjectName = objectName
+	if root != syscall.InvalidHandle {
+		o.RootDirectory = root
+	}
+	o.Length = uint32(unsafe.Sizeof(*o))
+	return nil
+}
+
 // Values for the Attributes member of OBJECT_ATTRIBUTES.
 const (
 	OBJ_INHERIT                       = 0x00000002
diff --git a/src/syscall/types_windows.go b/src/syscall/types_windows.go
index 6743675b95..eb1ba06ce6 100644
--- a/src/syscall/types_windows.go
+++ b/src/syscall/types_windows.go
@@ -34,18 +34,20 @@ const (
 
 const (
 	// Invented values to support what package os expects.
-	O_RDONLY   = 0x00000
-	O_WRONLY   = 0x00001
-	O_RDWR     = 0x00002
-	O_CREAT    = 0x00040
-	O_EXCL     = 0x00080
-	O_NOCTTY   = 0x00100
-	O_TRUNC    = 0x00200
-	O_NONBLOCK = 0x00800
-	O_APPEND   = 0x00400
-	O_SYNC     = 0x01000
-	O_ASYNC    = 0x02000
-	O_CLOEXEC  = 0x80000
+	O_RDONLY       = 0x00000
+	O_WRONLY       = 0x00001
+	O_RDWR         = 0x00002
+	O_CREAT        = 0x00040
+	O_EXCL         = 0x00080
+	O_NOCTTY       = 0x00100
+	O_TRUNC        = 0x00200
+	O_NONBLOCK     = 0x00800
+	O_APPEND       = 0x00400
+	O_SYNC         = 0x01000
+	O_ASYNC        = 0x02000
+	O_CLOEXEC      = 0x80000
+	o_DIRECTORY    = 0x100000   // used by internal/syscall/windows
+	o_NOFOLLOW_ANY = 0x20000000 // used by internal/syscall/windows
 )
 
 const (