syscall: support more flags when opening directories on Windows

syscall.Open was artificially limiting the flags that were eligible
to open directories on Windows. This change extend the cases where we
pass FILE_FLAG_BACKUP_SEMANTICS to all flag combinations allowed by
Unix.

Change-Id: Ia7c083bcba070f92ea61c6d67487bdefd0d99546
Reviewed-on: https://go-review.googlesource.com/c/go/+/619295
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Damien Neil <dneil@google.com>

diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go
index 84d6550c1633e6993bf4ba824520bbfb6bfdf706..db1f4f2ba4d2cbee083ed0ddf97197c5e50c2a75 100644 (file)
--- a/src/syscall/syscall_windows.go
+++ b/src/syscall/syscall_windows.go
@@ -388,8 +388,10 @@ func Open(name string, flag int, perm uint32) (fd Handle, err error) {
        if perm&S_IWRITE == 0 {
                attrs = FILE_ATTRIBUTE_READONLY
        }
-       if createmode == OPEN_EXISTING && access == GENERIC_READ {
-               // Necessary for opening directory handles.
+       if flag&O_WRONLY == 0 && flag&O_RDWR == 0 {
+               // We might be opening or creating a directory.
+               // CreateFile requires FILE_FLAG_BACKUP_SEMANTICS
+               // to work with directories.
                attrs |= FILE_FLAG_BACKUP_SEMANTICS
        }
        if flag&O_SYNC != 0 {

diff --git a/src/syscall/syscall_windows_test.go b/src/syscall/syscall_windows_test.go
index 03821ea594d8be7666ed4e1577b84bdec5766f75..ea1e8c9b3c2fa5d3e609d2b67d7b9070569bb699 100644 (file)
--- a/src/syscall/syscall_windows_test.go
+++ b/src/syscall/syscall_windows_test.go
@@ -24,8 +24,8 @@ func TestOpen_Dir(t *testing.T) {
                err  error
        }{
                {syscall.O_RDONLY, nil},
-               {syscall.O_CREAT, syscall.ERROR_ACCESS_DENIED},                    // TODO(qmuntal): should be allowed.
-               {syscall.O_RDONLY | syscall.O_CREAT, syscall.ERROR_ACCESS_DENIED}, // TODO(qmuntal): should be allowed.
+               {syscall.O_CREAT, nil},
+               {syscall.O_RDONLY | syscall.O_CREAT, nil},
                {syscall.O_RDONLY | syscall.O_TRUNC, syscall.ERROR_ACCESS_DENIED},
                {syscall.O_WRONLY | syscall.O_RDWR, syscall.EISDIR},
                {syscall.O_WRONLY, syscall.EISDIR},