Cygwin: align renameat2 to Linux behaviour

In contrast to rename default behaviour, Linux' renameat2 returns -1
with errno set to EEXIST, if oldfile and newfile refer to the same
file, and the RENAME_NOREPLACE flag is set.

Follow suit, given this is a Linux-only function anyway.

Fixes: f665b1cef30f ("cygwin: Implement renameat2")
Reported-by: Bruno Haible <bruno@clisp.org>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

2 files changed, 17 insertions, 5 deletions

diff --git a/winsup/cygwin/release/3.4.7 b/winsup/cygwin/release/3.4.7
index 7bc7d4a..0e69221 100644
--- a/winsup/cygwin/release/3.4.7
+++ b/winsup/cygwin/release/3.4.7
@@ -21,3 +21,7 @@ Bug Fixes
 
 - Fix error handling in readlinkat.
   Addresses: https://cygwin.com/pipermail/cygwin/2023-April/253510.html
+
+- Fix return code and errno set by renameat2, if oldfile and newfile
+  refer to the same file, and the RENAME_NOREPLACE flag is set.
+  Addresses: https://cygwin.com/pipermail/cygwin/2023-April/253514.html
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index a4e4af6..5adc614 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -2122,6 +2122,14 @@ nt_path_has_executable_suffix (PUNICODE_STRING upath)
   return false;
 }
 
+inline int
+set_same_file_return (bool noreplace)
+{
+  if (!noreplace)
+    return 0;
+  set_errno (EEXIST);
+  return -1;
+}
 /* If newpath names an existing file and the RENAME_NOREPLACE flag is
    specified, fail with EEXIST.  Exception: Don't fail if the purpose
    of the rename is just to change the case of oldpath on a
@@ -2300,7 +2308,7 @@ rename2 (const char *oldpath, const char *newpath, unsigned int at2flags)
 				     newpc.get_nt_native_path (),
 				     FALSE))
 	    {
-	      res = 0;
+	      res = set_same_file_return (noreplace);
 	      __leave;
 	    }
 	  newpc.file_attributes (INVALID_FILE_ATTRIBUTES);
@@ -2315,7 +2323,7 @@ rename2 (const char *oldpath, const char *newpath, unsigned int at2flags)
 	      if (newpc.get_nt_native_path ()->Length
 		  == oldpc.get_nt_native_path ()->Length)
 		{
-		  res = 0;
+		  res = set_same_file_return (noreplace);
 		  __leave;
 		}
 	      if (*(PWCHAR) ((PBYTE) newpc.get_nt_native_path ()->Buffer
@@ -2335,7 +2343,7 @@ rename2 (const char *oldpath, const char *newpath, unsigned int at2flags)
 					 newpc.get_nt_native_path (),
 					 oldpc.objcaseinsensitive ()))
 		{
-		  res = 0;
+		  res = set_same_file_return (noreplace);
 		  __leave;
 		}
 	    }
@@ -2364,7 +2372,7 @@ rename2 (const char *oldpath, const char *newpath, unsigned int at2flags)
 					 newpc.get_nt_native_path (),
 					 oldpc.objcaseinsensitive ()))
 		{
-		  res = 0;
+		  res = set_same_file_return (noreplace);
 		  __leave;
 		}
 	    }
@@ -2582,7 +2590,7 @@ skip_pre_W10_checks:
 	    {
 	      debug_printf ("%s and %s are the same file", oldpath, newpath);
 	      NtClose (nfh);
-	      res = 0;
+	      res = set_same_file_return (noreplace);
 	      __leave;
 	    }
 	  NtClose (nfh);