os,internal/syscall/windows: support O_* flags in Root.OpenFile

These file flags are supported by os.OpenFile since CL 699415.

Closes #73676

Change-Id: Ib37102a565f538d394d2a94bd605d6c6004f3028
Reviewed-on: https://go-review.googlesource.com/c/go/+/724621
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

2 files changed, 54 insertions, 10 deletions

diff --git a/src/internal/syscall/windows/at_windows.go b/src/internal/syscall/windows/at_windows.go
index b7ca8433c2..de733c523c 100644
--- a/src/internal/syscall/windows/at_windows.go
+++ b/src/internal/syscall/windows/at_windows.go
@@ -5,6 +5,7 @@
 package windows
 
 import (
+	"internal/oserror"
 	"runtime"
 	"structs"
 	"syscall"
@@ -26,7 +27,6 @@ const (
 // to avoid overlap.
 const (
 	O_NOFOLLOW_ANY = 0x200000000 // disallow symlinks anywhere in the path
-	O_OPEN_REPARSE = 0x400000000 // FILE_OPEN_REPARSE_POINT, used by Lstat
 	O_WRITE_ATTRS  = 0x800000000 // FILE_WRITE_ATTRIBUTES, used by Chmod
 )
 
@@ -36,24 +36,54 @@ func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ sysc
 	}
 
 	var access, options uint32
+	// Map Win32 file flags to NT create options.
+	fileFlags := uint32(flag) & FileFlagsMask
+	if fileFlags&^ValidFileFlagsMask != 0 {
+		return syscall.InvalidHandle, oserror.ErrInvalid
+	}
+	if fileFlags&O_FILE_FLAG_OVERLAPPED == 0 {
+		options |= FILE_SYNCHRONOUS_IO_NONALERT
+	}
+	if fileFlags&O_FILE_FLAG_DELETE_ON_CLOSE != 0 {
+		access |= DELETE
+	}
+	setOptionFlag := func(ntFlag, win32Flag uint32) {
+		if fileFlags&win32Flag != 0 {
+			options |= ntFlag
+		}
+	}
+	setOptionFlag(FILE_NO_INTERMEDIATE_BUFFERING, O_FILE_FLAG_NO_BUFFERING)
+	setOptionFlag(FILE_WRITE_THROUGH, O_FILE_FLAG_WRITE_THROUGH)
+	setOptionFlag(FILE_SEQUENTIAL_ONLY, O_FILE_FLAG_SEQUENTIAL_SCAN)
+	setOptionFlag(FILE_RANDOM_ACCESS, O_FILE_FLAG_RANDOM_ACCESS)
+	setOptionFlag(FILE_OPEN_FOR_BACKUP_INTENT, O_FILE_FLAG_BACKUP_SEMANTICS)
+	setOptionFlag(FILE_SESSION_AWARE, O_FILE_FLAG_SESSION_AWARE)
+	setOptionFlag(FILE_DELETE_ON_CLOSE, O_FILE_FLAG_DELETE_ON_CLOSE)
+	setOptionFlag(FILE_OPEN_NO_RECALL, O_FILE_FLAG_OPEN_NO_RECALL)
+	setOptionFlag(FILE_OPEN_REPARSE_POINT, O_FILE_FLAG_OPEN_REPARSE_POINT)
+
 	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
+		access |= FILE_GENERIC_READ
 	case syscall.O_WRONLY:
-		access = FILE_GENERIC_WRITE
+		access |= FILE_GENERIC_WRITE
 		options |= FILE_NON_DIRECTORY_FILE
 	case syscall.O_RDWR:
-		access = FILE_GENERIC_READ | FILE_GENERIC_WRITE
+		access |= FILE_GENERIC_READ | FILE_GENERIC_WRITE
 		options |= FILE_NON_DIRECTORY_FILE
 	default:
 		// Stat opens files without requesting read or write permissions,
 		// but we still need to request SYNCHRONIZE.
-		access = SYNCHRONIZE
+		access |= SYNCHRONIZE
 	}
 	if flag&syscall.O_CREAT != 0 {
 		access |= FILE_GENERIC_WRITE
 	}
+	if fileFlags&O_FILE_FLAG_NO_BUFFERING != 0 {
+		// Disable buffering implies no implicit append access.
+		access &^= FILE_APPEND_DATA
+	}
 	if flag&syscall.O_APPEND != 0 {
 		access |= FILE_APPEND_DATA
 		// Remove FILE_WRITE_DATA access unless O_TRUNC is set,
@@ -82,14 +112,13 @@ func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ sysc
 	if flag&syscall.O_CLOEXEC == 0 {
 		objAttrs.Attributes |= OBJ_INHERIT
 	}
+	if fileFlags&O_FILE_FLAG_POSIX_SEMANTICS == 0 {
+		objAttrs.Attributes |= OBJ_CASE_INSENSITIVE
+	}
 	if err := objAttrs.init(dirfd, name); err != nil {
 		return syscall.InvalidHandle, err
 	}
 
-	if flag&O_OPEN_REPARSE != 0 {
-		options |= FILE_OPEN_REPARSE_POINT
-	}
-
 	// 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.
@@ -121,7 +150,7 @@ func Openat(dirfd syscall.Handle, name string, flag uint64, perm uint32) (_ sysc
 		fileAttrs,
 		FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
 		disposition,
-		FILE_SYNCHRONOUS_IO_NONALERT|FILE_OPEN_FOR_BACKUP_INTENT|options,
+		FILE_OPEN_FOR_BACKUP_INTENT|options,
 		nil,
 		0,
 	)
diff --git a/src/internal/syscall/windows/types_windows.go b/src/internal/syscall/windows/types_windows.go
index 49daf9b31b..568f94624c 100644
--- a/src/internal/syscall/windows/types_windows.go
+++ b/src/internal/syscall/windows/types_windows.go
@@ -210,6 +210,7 @@ const (
 	FILE_NO_COMPRESSION            = 0x00008000
 	FILE_OPEN_REQUIRING_OPLOCK     = 0x00010000
 	FILE_DISALLOW_EXCLUSIVE        = 0x00020000
+	FILE_SESSION_AWARE             = 0x00040000
 	FILE_RESERVE_OPFILTER          = 0x00100000
 	FILE_OPEN_REPARSE_POINT        = 0x00200000
 	FILE_OPEN_NO_RECALL            = 0x00400000
@@ -286,3 +287,17 @@ const VER_NT_WORKSTATION = 0x0000001
 type MemoryBasicInformation = windows.MemoryBasicInformation
 
 type Context = windows.Context
+
+const FileFlagsMask = 0xFFF00000
+
+const ValidFileFlagsMask = O_FILE_FLAG_OPEN_REPARSE_POINT |
+	O_FILE_FLAG_BACKUP_SEMANTICS |
+	O_FILE_FLAG_OVERLAPPED |
+	O_FILE_FLAG_OPEN_NO_RECALL |
+	O_FILE_FLAG_SESSION_AWARE |
+	O_FILE_FLAG_POSIX_SEMANTICS |
+	O_FILE_FLAG_DELETE_ON_CLOSE |
+	O_FILE_FLAG_SEQUENTIAL_SCAN |
+	O_FILE_FLAG_NO_BUFFERING |
+	O_FILE_FLAG_RANDOM_ACCESS |
+	O_FILE_FLAG_WRITE_THROUGH