trans/mtab: do not include non-filesystem translators by default

Traditionally, /proc/mounts includes only filesystem mount points.
Previously though, the mtab translator included any kind of
translator, like all /hurd/storeio translators.  This causes problems
with umount --all as this would remove the passive translator records
from nodes in /dev.

Fix this by only listing filesystem-like translators by default.
Filesystem-like translators are identified by their response to
dir_readdir messages sent to their root node.

* trans/mtab.c (all_translators): New variable.
(options): Add flag to preserve the old behavior.
(parse_opt): Handle the new flag.
(is_filesystem_translator): New function.
(mtab_populate): Skip non-filesystem translators by default.

1 files changed, 40 insertions, 0 deletions

diff --git a/trans/mtab.c b/trans/mtab.c
index adfb3458..75ef1d3a 100644
--- a/trans/mtab.c
+++ b/trans/mtab.c
@@ -40,6 +40,7 @@
 
 static char *target_path = NULL;
 static int insecure = 0;
+static int all_translators = 0;
 
 /* Our control port.  */
 struct trivfs_control *control;
@@ -60,6 +61,9 @@ static const struct argp_option options[] =
 {
   {"insecure", 'I', 0, 0,
    "Follow translators not bound to nodes owned by you or root"},
+  {"all-translators", 'A', 0, 0,
+   "List all translators, even those that are probably not "
+   "filesystem translators"},
   {}
 };
 
@@ -72,6 +76,10 @@ error_t parse_opt (int key, char *arg, struct argp_state *state)
       insecure = 1;
       break;
 
+    case 'A':
+      all_translators = 1;
+      break;
+
     case ARGP_KEY_ARG:
       target_path = realpath (arg, NULL);
       if (! target_path)
@@ -277,6 +285,32 @@ mtab_add_entry (struct mtab *mtab, const char *entry, size_t length)
   return 0;
 }
 
+/* Check whether the given NODE is a directory on a filesystem
+   translator.  */
+static boolean_t
+is_filesystem_translator (file_t node)
+{
+  error_t err;
+  char *data = NULL;
+  size_t datacnt = 0;
+  int amount;
+  err = dir_readdir (node, &data, &datacnt, 0, 1, 0, &amount);
+  if (data != NULL && datacnt > 0)
+    vm_deallocate (mach_task_self (), (vm_address_t) data, datacnt);
+
+  /* Filesystem translators return either no error, or, if NODE has
+     not been looked up with O_READ, EBADF to dir_readdir
+     requests.  */
+  switch (err)
+    {
+    case 0:
+    case EBADF:
+      return TRUE;
+    default:
+      return FALSE;
+    }
+}
+
 /* Populates the given MTAB object with the information for PATH.  If
    INSECURE is given, also follow translators bound to nodes not owned
    by root or the current user.  */
@@ -333,6 +367,12 @@ mtab_populate (struct mtab *mtab, const char *path, int insecure)
       goto errout;
     }
 
+  if (! (all_translators || is_filesystem_translator (node)))
+    {
+      err = 0;
+      goto errout;
+    }
+
   /* Query its options.	 */
   err = file_get_fs_options (node, &argz, &argz_len);
   if (err)