driver/bareboxdriver: change default interrupt key to CTRL+D

For developer convenience, barebox v2022.11.0 onwards brings up network
interfaces automatically in the background when the boot is aborted by
user input. By the time a user then runs boot net for example, the
seconds it takes for an Ethernet link to be established will have passed.

The effects of this have already been seen in Labgrid;
Commit 6f7bf66 ("driver/bareboxdriver: silence barebox in
_await_prompt() and unsilence on boot()") changes the log level to
suppress "ethX: N Mbps ... link detected" messages, but it leaves
another problem unaddressed: A system that Labgrid aborts to run the
boot command now behaves differently to a system that was left to boot
normally, because network adapters are reconfigured that normally aren't.

This bit me while trying to use Labgrid to debug a network issue in
Linux as barebox ifup changed the Linux behavior.

barebox v2025.03.0 introduces a new halt state that can be entered by
ctrl-d that skips these automatic hooks. Using it should not introduce
regressions for existing users, regardless of barebox version:

- Prior to barebox v2025.01.0, the only options for an abort key were
  ctrl-c or any and both line feed and CTRL+D behave the same with either
  option.

- After v2025.01.0, global.autoboot_abort_key can be set to an arbitrary
  single printable ASCII key and it seems not possible to set a new line
  this way.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Author: a3f

CHANGES.rst

@@ -1,3 +1,14 @@
+Release 25.1 (Unreleased)
+-------------------------
+
+New Features in 25.1
+~~~~~~~~~~~~~~~~~~~~
+
+- The default interrupt key for the `BareboxDriver` is now CTRL+D (``\x04``)
+  instead of a line feed (``\n``). barebox v2025.03.0 onwards handles
+  CTRL+D specially to halt autoboot countdown without running interactive
+  hooks like bringing up network interfaces automatically.
+
 Release 25.0 (Released May 7, 2025)
 -----------------------------------
 As announced `before

labgrid/driver/bareboxdriver.py

@@ -32,7 +32,7 @@ class BareboxDriver(CommandMixin, Driver, CommandProtocol, LinuxBootProtocol):
     bindings = {"console": ConsoleProtocol, }
     prompt = attr.ib(default="", validator=attr.validators.instance_of(str))
     autoboot = attr.ib(default="stop autoboot", validator=attr.validators.instance_of(str))
-    interrupt = attr.ib(default="\n", validator=attr.validators.instance_of(str))
+    interrupt = attr.ib(default="\x04", validator=attr.validators.instance_of(str))
     bootstring = attr.ib(default=r"Linux version \d", validator=attr.validators.instance_of(str))
     password = attr.ib(default="", validator=attr.validators.instance_of(str))
     login_timeout = attr.ib(default=60, validator=attr.validators.instance_of(int))