Don't fail in acl_set_file on MS-Windows if the operation is a no-op.

 src/w32.c (acl_set_file): If setting the file security descriptor
 fails, and the new DACL is identical to the existing one, silently
 return success.  This fixes problems for users backing up their
 own files without having the necessary privileges for setting
 security descriptors.

2 files changed, 31 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index c7502104ddf..648f14a61e4 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,11 @@
 2012-12-23  Eli Zaretskii  <eliz@gnu.org>
 
+        * w32.c (acl_set_file): If setting the file security descriptor
+        fails, and the new DACL is identical to the existing one, silently
+        return success.  This fixes problems for users backing up their
+        own files without having the necessary privileges for setting
+        security descriptors.
+
         * w32proc.c (reader_thread): Do not index fd_info[] with negative
         values.
         (reader_thread): Exit when cp->status becomes STATUS_READ_ERROR
diff --git a/src/w32.c b/src/w32.c
index 47b950668b0..9ebc97088d0 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -4876,8 +4876,31 @@ acl_set_file (const char *fname, acl_type_t type, acl_t acl)
       retval = 0;
       errno = e;
     }
-  else if (err == ERROR_INVALID_OWNER)
-    errno = EPERM;
+  else if (err == ERROR_INVALID_OWNER || err == ERROR_NOT_ALL_ASSIGNED)
+    {
+      /* Maybe the requested ACL and the one the file already has are
+         identical, in which case we can silently ignore the
+         failure.  (And no, Windows doesn't.)  */
+      acl_t current_acl = acl_get_file (fname, ACL_TYPE_ACCESS);
+
+      errno = EPERM;
+      if (current_acl)
+        {
+          char *acl_from = acl_to_text (current_acl, NULL);
+          char *acl_to = acl_to_text (acl, NULL);
+
+          if (acl_from && acl_to && xstrcasecmp (acl_from, acl_to) == 0)
+            {
+              retval = 0;
+              errno = e;
+            }
+          if (acl_from)
+            acl_free (acl_from);
+          if (acl_to)
+            acl_free (acl_to);
+          acl_free (current_acl);
+        }
+    }
   else if (err == ERROR_FILE_NOT_FOUND || err == ERROR_PATH_NOT_FOUND)
     errno = ENOENT;