Add a check for binfmt_misc (#1236)

Closes #1223.

pmb/chroot/binfmt.py

@@ -20,6 +20,7 @@ import os
 import logging
 
 import pmb.helpers.run
+import pmb.helpers.other
 import pmb.parse
 import pmb.parse.arch
 
@@ -35,6 +36,7 @@ def register(args, arch):
     arch_debian = pmb.parse.arch.alpine_to_debian(arch)
     if is_registered(arch_debian):
         return
+    pmb.helpers.other.check_binfmt_misc(args)
     pmb.chroot.apk.install(args, ["qemu-user-static-repack",
                                   "qemu-user-static-repack-binfmt"])
     info = pmb.parse.binfmt_info(args, arch_debian)

pmb/helpers/other.py

@@ -61,6 +61,23 @@ def check_grsec(args):
                        " more details: <" + link + ">")
 
 
+def check_binfmt_misc(args):
+    """
+    Check if the 'binfmt_misc' module is loaded by checking, if
+    /proc/sys/fs/binfmt_misc/ exists. If it exists, then do nothing.
+    Otherwise, raise an exception pointing to user to the Wiki.
+    """
+    path = "/proc/sys/fs/binfmt_misc/"
+    if os.path.exists(path):
+        return
+
+    link = "https://postmarketos.org/binfmt_misc"
+    raise RuntimeError("It appears that your system has not loaded the"
+                       " module 'binfmt_misc'. This is required to run"
+                       " foreign architecture programs with QEMU (eg."
+                       " armhf on x86_64):\n See: <" + link + ">")
+
+
 def migrate_success(args):
     logging.info("Migration done")
     with open(args.work + "/version", "w") as handle: