[newlib-cygwin/main] Cygwin: don't use unlink/rename POSIX semantics on certain NTFS

[newlib-cygwin/main] Cygwin: don't use unlink/rename POSIX semantics on certain NTFS

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=fe2545e9faaf4bf9586f61a7b83d5cb5af501194

commit fe2545e9faaf4bf9586f61a7b83d5cb5af501194
Author:     Corinna Vinschen <corinna@vinschen.de>
AuthorDate: Tue Mar 21 18:29:59 2023 +0100
Commit:     Corinna Vinschen <corinna@vinschen.de>
CommitDate: Tue Mar 21 18:29:59 2023 +0100

    Cygwin: don't use unlink/rename POSIX semantics on certain NTFS
    
    If a host NTFS is mapped into a Hyper-V isolated container, the
    OPEN_BY_FILE_ID filesystem flag is missing, just as if that NTFS
    is a remote drive.  However, NtQueryVolumeInformationFile claims
    the drive is a local drive.
    
    We can use this fact to learn that the process is running under
    Hyper-V, and that the Hyper-V isolated process can't use rename/unlink
    with POSIX semantics.  Strange enough, the POSIX_UNLINK_RENAME filesystem
    flag is still set...
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/syscalls.cc | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index af4f870851eb..3e2d42f3aa8b 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -691,10 +691,12 @@ unlink_nt (path_conv &pc, bool shareable)
   pc.get_object_attr (attr, sec_none_nih);
 
   /* First check if we can use POSIX unlink semantics: W10 1709+, local NTFS.
-     With POSIX unlink semantics the entire job gets MUCH easier and faster.
-     Just try to do it and if it fails, it fails. */
+     For the OPEN_BY_FILE_ID flag, see MINIMAL_WIN_NTFS_FLAGS comment in
+     fs_info::update.  With POSIX unlink semantics the entire job gets MUCH
+     easier and faster.  Just try to do it and if it fails, it fails. */
   if (wincap.has_posix_unlink_semantics ()
-      && !pc.isremote () && pc.fs_is_ntfs ())
+      && !pc.isremote () && pc.fs_is_ntfs ()
+      && pc.has_attribute (FILE_SUPPORTS_OPEN_BY_FILE_ID))
     {
       FILE_DISPOSITION_INFORMATION_EX fdie;
 
@@ -2407,10 +2409,12 @@ rename2 (const char *oldpath, const char *newpath, unsigned int at2flags)
 	  __leave;
 	}
 
-      /* POSIX semantics only on local NTFS drives. */
+      /* POSIX semantics only on local NTFS drives. For the OPEN_BY_FILE_ID
+         flag, see MINIMAL_WIN_NTFS_FLAGS comment in fs_info::update. */
       use_posix_semantics = wincap.has_posix_rename_semantics ()
 			    && !oldpc.isremote ()
-			    && oldpc.fs_is_ntfs ();
+			    && oldpc.fs_is_ntfs ()
+			    && oldpc.has_attribute (FILE_SUPPORTS_OPEN_BY_FILE_ID);
 
       /* Opening the file must be part of the transaction.  It's not sufficient
 	 to call only NtSetInformationFile under the transaction.  Therefore we