confine xlink behavior behind its volflag

symlinks between volumes will only be created if xlink is
enabled, so such symlinks should be ignored if xlink is
disabled, as they might originate from other software

this prevents accidental rewriting of non-dedup symlinks

copyparty/up2k.py

@@ -3755,8 +3755,11 @@ def _handle_rm(
                     cur = None
                     try:
                         ptop = dbv.realpath
+                        xlink = bool(dbv.flags.get("xlink"))
                         cur, wark, _, _, _, _ = self._find_from_vpath(ptop, volpath)
-                        self._forget_file(ptop, volpath, cur, wark, True, st.st_size)
+                        self._forget_file(
+                            ptop, volpath, cur, wark, True, st.st_size, xlink
+                        )
                     finally:
                         if cur:
                             cur.connection.commit()
@@ -3980,13 +3983,15 @@ def _mv_file(
             if c2 and c2 != c1:
                 self._copy_tags(c1, c2, w)
 
+            xlink = bool(svn.flags.get("xlink"))
+
             with self.reg_mutex:
                 has_dupes = self._forget_file(
-                    svn.realpath, srem, c1, w, is_xvol, fsize_ or fsize
+                    svn.realpath, srem, c1, w, is_xvol, fsize_ or fsize, xlink
                 )
 
             if not is_xvol:
-                has_dupes = self._relink(w, svn.realpath, srem, dabs)
+                has_dupes = self._relink(w, svn.realpath, srem, dabs, c1, xlink)
 
             curs.add(c1)
 
@@ -4129,6 +4134,7 @@ def _forget_file(
         wark: Optional[str],
         drop_tags: bool,
         sz: int,
+        xlink: bool,
     ) -> bool:
         """
         mutex(main,reg) me
@@ -4140,7 +4146,7 @@ def _forget_file(
         if wark and cur:
             self.log("found {} in db".format(wark))
             if drop_tags:
-                if self._relink(wark, ptop, vrem, ""):
+                if self._relink(wark, ptop, vrem, "", cur, xlink):
                     has_dupes = True
                     drop_tags = False
 
@@ -4172,7 +4178,15 @@ def _forget_file(
 
         return has_dupes
 
-    def _relink(self, wark: str, sptop: str, srem: str, dabs: str) -> int:
+    def _relink(
+        self,
+        wark: str,
+        sptop: str,
+        srem: str,
+        dabs: str,
+        vcur: Optional["sqlite3.Cursor"],
+        xlink: bool,
+    ) -> int:
         """
         update symlinks from file at svn/srem to dabs (rename),
         or to first remaining full if no dabs (delete)
@@ -4188,6 +4202,8 @@ def _relink(self, wark: str, sptop: str, srem: str, dabs: str) -> int:
             argv = (wark[:16], wark)
 
         for ptop, cur in self.cur.items():
+            if not xlink and cur and cur != vcur:
+                continue
             for rd, fn in cur.execute(q, argv):
                 if rd.startswith("//") or fn.startswith("//"):
                     rd, fn = s3dec(rd, fn)