chroot: add --usb flag to make usb devices available (MR 2554)

Add a flag to bind-mount in the necessary sysfs directories for USB
devices to be accessed inside the chroot. This is the same as how we do
it for "pmbootstrap flasher" but allows running arbitrary commands in
the chroot.

This is useful to allow using pmbootstrap chroot's as a sandbox for
custom flashing procedures.

Signed-off-by: Caleb Connolly <caleb@postmarketos.org>

pmb/helpers/frontend.py

@@ -27,6 +27,7 @@ import pmb.helpers.devices
 import pmb.helpers.git
 import pmb.helpers.lint
 import pmb.helpers.logging
+import pmb.helpers.mount
 import pmb.helpers.pmaports
 import pmb.helpers.repo
 import pmb.helpers.repo_missing
@@ -211,6 +212,11 @@ def chroot(args: PmbArgs) -> None:
         size_reserve = 2048  # 2 GiB
         pmb.install.blockdevice.create_and_mount_image(args, size_boot, size_root, size_reserve)
 
+    # Bind mount in sysfs dirs to accessing USB devices (e.g. for running fastboot)
+    if args.chroot_usb:
+        for folder in pmb.config.flash_mount_bind:
+            pmb.helpers.mount.bind(folder, Chroot.native() / folder)
+
     pmb.helpers.apk.update_repository_list(chroot.path, user_repository=True)
 
     # Run the command as user/root

pmb/parse/arguments.py

@@ -1102,6 +1102,12 @@ def get_parser() -> argparse.ArgumentParser:
         help="Mount the rootfs image and treat it like a normal chroot.",
         action="store_true",
     )
+    chroot.add_argument(
+        "--usb",
+        help="Make USB devices accessible inside the chroot.",
+        action="store_true",
+        dest="chroot_usb",
+    )
     chroot.add_argument(
         "command",
         default=["sh", "-i"],

pmb/types.py

@@ -78,6 +78,7 @@ class PmbArgs(Namespace):
     built: bool
     ccache: bool
     ccache_size: str
+    chroot_usb: bool
     cipher: str
     clear_log: bool
     cmdline: str