contrib/find_struct_file.py: also look in binfmt_misc

This is a surprising place where file references can be hiding that I've
run into before. There are some beginnings of an lsof-like script here.

Signed-off-by: Omar Sandoval <osandov@osandov.com>

contrib/find_struct_file.py

@@ -2,22 +2,41 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
-"""Find what process is using a struct file *, given as an address."""
+"""Print what is using a struct file *, given as an address."""
 
+import os
 import sys
 
 from drgn import Object
 from drgn.helpers.linux.fs import for_each_file
+from drgn.helpers.linux.list import list_for_each_entry
 from drgn.helpers.linux.pid import for_each_task
 
-file = Object(prog, "struct file *", int(sys.argv[1], 0))
-for task in for_each_task(prog):
-    for fd, file2 in for_each_file(task):
-        if file2 == file:
-            break
-    else:
-        continue
-    break
-else:
-    print("Not found:(")
-print(f"PID {task.pid.value_()} COMM {task.comm.string_().decode()} FD {fd}")
+
+def find_struct_file_fds(file: Object) -> None:
+    for task in for_each_task(file.prog_):
+        for fd, fd_file in for_each_file(task):
+            if fd_file == file:
+                print(
+                    f"PID {task.pid.value_()} COMM {task.comm.string_().decode()} FD {fd}"
+                )
+
+
+def find_struct_file_binfmt_misc(file: Object) -> None:
+    prog = file.prog_
+    for node in list_for_each_entry(
+        prog.type("Node", filename="binfmt_misc.c"),
+        prog.object("entries", filename="binfmt_misc.c").address_of_(),
+        "list",
+    ):
+        if node.interp_file == file:
+            print(f"binfmt_misc {os.fsdecode(node.name.string_())}")
+
+
+def find_struct_file(file: Object) -> None:
+    find_struct_file_fds(file)
+    find_struct_file_binfmt_misc(file)
+
+
+if __name__ == "__main__":
+    find_struct_file(Object(prog, "struct file *", int(sys.argv[1], 0)))