bits-2070 released with these changes:

Highlights of the new release:

  • BITS on EFI now supports TCP networking, including HTTP clients via urllib2, and HTTP servers via BaseHTTPServer. See below for details and caveats.

  • BITS now has significantly improved Python and ACPI performance, thanks to Python's optimized memory allocator. This speeds up common Python and ACPI operations significantly, including BITS boot time. BITS can now boot in less than a second on virtual hardware.

  • BITS line-editing keys now work on EFI, and several more common keybindings from readline now work in BITS. Refer to Documentation/line-editing.txt in the BITS distribution for full input documentation.

  • Fix a hard-to-debug issue that led to crashes or malfunctions in FFI calls between C and Python, caused by EFI interrupts during assembly code corrupting stack data in the x86-64 POSIX ABI "red zone".

  • BITS now has a mailing list,; see to subscribe.


BITS on EFI now supports TCP networking, using the Python socket module and various modules built atop it. On EFI systems that provide EFI_IP4_CONFIG_PROTOCOL and EFI_TCP4_SERVICE_BINDING_PROTOCOL, we implement a _socket module in Python with support for TCP sockets over IPv4. We then include Python's higher-level socket module that runs on top of _socket.

When constructing a socket for the first time, _socket will initialize the EFI network stack, which will typically use DHCP to obtain an address.

Given a socket created with s = socket.socket(), you can establish an outbound connection with s.connect((""), port), or create a server using s.bind(("", port)), s.listen(1), and client_s, addr = s.accept(). Afterwards, use recv and sendall to communicate, or create a file-like object with makefile. See the socket module documentation at for more details.

The efi module now includes the EFI protocols for IPv4 configuration, TCP over IPv4, and IPv4 DNS. The current Python socket implementation only supports TCP over IPv4. Also, as OVMF and other EFI systems do not include EFI_DNS4_SERVICE_BINDING_PROTOCOL, the socket implementation does not support hostname resolution (other than "localhost").

Both blocking and non-blocking sockets work. BITS now includes a safe Python interface to handle EFI events via callbacks, and uses this to implement sockets and the Python select module ( only).

For the receive side, EFI has no way to ask for available data without retrieving that data, so BITS will always kick off an EFI Receive call in the background when checking for socket readiness with no data available, and buffer the received data to supply to the caller. A blocking recv will wait for the data to come back; a non-blocking recv will raise a timeout after the configured socket timeout (possibly immediately), and a subsequent recv will return the data. Only one outstanding Receive call will run at a time, and only if BITS does not already have a buffer of received data.

For the transmit side, a connected socket will always show up as writable. BITS does not buffer transmits itself, but instead always blocks until the EFI Transmit call signals its completion event.

Non-blocking connect works as well; on a connecting socket for write will block until the connect completes, and a subsequent call to getsockopt(SOL_SOCKET, SO_ERROR) will return (and clear) the connection status.

For simplicity, do not attempt to reuse a caller's buffers for zero-copy networking; this is several-copy networking, optimized for simplicity and memory usage rather than performance.

Building on this networking support, BITS now supports the Python urllib2 module and its dependencies, to function as a simple HTTP client. This also includes the Python modules urllib, urlparse, httplib, mimetools, and rfc822.

Since BITS does not include DNS support, using urllib2.urlopen on an URL with a hostname will fail. An URL with an IP address works, as long as the server on the other end can handle a Host header with that IP address (which may fail with servers serving multiple domains using name-based virtual hosting). As a simple test, connecting to a server run via python's SimpleHTTPServer module works, which makes it simple to transfer data from a separate host system into the BITS environment without rebooting.

Since BITS does not include an SSL library, urllib2.urlopen does not support https URLs.

urllib2's support for digest authentication uses the random module, which we don't yet support; add a stub random module with no functions, so that importing urllib2 will work, but attempting to use digest authentication will raise an exception when attempting to call non-existent functions in random.

Likewise, mimetools imports tempfile, but only calls it from mimetools.pipethrough (which also calls the unsupported os.popen); add a stub tempfile module with no functions. httplib uses mimetools.Message, which works.

On the server side, BITS now supports the Python BaseHTTPServer module and its dependencies, to build simple HTTP servers. This includes the Python modules base64, hashlib, cgi, mimetypes, shutil, dummy_threading (without actual threading support), and SocketServer. To build a simple HTTP server, define a class deriving from BaseHTTPServer.BaseHTTPRequestHandler that implements handler methods for GET (and POST if desired), and pass that class to BaseHTTPServer.test. See the Python BaseHTTPServer documentation at for details.

Note that since the sockets support does not yet support SO_REUSEADDR (the flag exists for compatibility, but does not yet map to any underlying EFI functionality), attempting to stop and immediately restart a server on the same port will likely fail with an EFI exception, indicating that the port remains in use.


BITS now enables Python's pymalloc allocator; this speeds up object allocations by an order of magnitude, which also affects common operations such as string concatenation. This reduces BITS boot time by an order of magnitude (now boots in about a second on virtual hardware), and provides similar speedups in every part of BITS and Python.

BITS also uses Python's small-object allocator to allocate small ACPI objects, which speeds up many ACPI operations.

Several of the longest-running tests in BITS, which measured CPU frequencies for many seconds to ensure a stable reading, will now optimistically attempt to use less wall-clock time if they get a stable reading more quickly, speeding up the BITS testsuite in the common case.

Line-editing keys

BITS now supports a much more extensive set of line-editing keys at the Python interactive prompt, on both EFI and BIOS systems; all of these keys match the behaviors expected by readline-trained fingers. Refer to Documentation/line-editing.txt in the BITS distribution for full input documentation. Highlights include Ctrl-Left and Ctrl-Right to move the cursor by words, Ctrl-O to run and retrieve successive lines from history, Ctrl-W/Ctrl-K/Ctrl-U/Ctrl-Y/Alt-Y to kill (delete) and yank (paste) text, and Ctrl-C to interrupt Python code in progress (only on EFI).

(Some of these keys previously worked on BIOS systems, but not on EFI due to input protocol limitations; BITS on EFI now supports and uses EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL to obtain keyboard input directly from the firmware.)

Ctrl-C support uses EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL to register a key notify handler for Ctrl-C, which raises KeyboardInterrupt the next time the Python interpreter has control. This allows aborting a long-running operation, which would otherwise require rebooting. Note that this cannot interrupt a long-running operation in C code or in firmware, and that not all code in BITS cleans up perfectly after a KeyboardInterrupt exception.

This introduces a new bits.input module to abstract keyboard input. On EFI platforms, this uses the EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL; on non-EFI BIOS, this continues to use GRUB for input.

Other enhancements

  • testacpi: Speed up the ACPI _PSS test

    Before spending a full second measuring the frequency of a CPU at a given pstate, measure it for 100ms, and pass if we get the expected result; only fall back to 1s if that fails. This significantly speeds up the pstate test, which we run as part of the default test suite.

  • pstate: Speed up the hardware pstate test

    Before spending a full second measuring the frequency of a CPU at a given pstate, measure it for 100ms, and pass if we get the expected result; only fall back to 1s if that fails. This significantly speeds up the hardware pstate test, which we run as part of the default test suite on supported CPUs.

  • Allow ACPI evaluation to read and write IO ports by default

    Some systems, such as the third-generation Lenovo X1 Carbon, loop forever performing IO-triggered SMIs during ACPI initialization; the default behavior of blocking IO ports causes such systems to hang when initializing ACPI. Since we already allow memory accesses by default, allow IO as well.

    For compatibility and debugging, acpi.evaluate still supports the unsafe_io keyword argument; unsafe_io=False will explicitly disable IO port access, and unsafe_io=True acts as a no-op for compatibility with existing code.

  • acpi: Implement OS port access functions in Python

    Replace the C implementations of AcpiOsReadPort and AcpiOsWritePort with calls to callback functions implemented in Python.

  • acpi: In ACPICA initialization, don't switch the system into ACPI mode

    With IO port accesses enabled by default, ACPICA now successfully switches the system into ACPI mode during initialization; previously, the IO write to make this transition got ignored. On some systems, switching into ACPI mode disables BIOS keyboard support, which BITS relies on. Explicitly disable this transition in ACPICA initialization, to return to the previous BITS behavior and keep the BIOS keyboard working.

  • ttypager: Show progress while collecting output

    The pager collects output from writes to stdout, but doesn't display anything until done. Add a spinning progress indicator to help the user tell the difference between long-running output generation and a hang.

  • Turn on Py_InspectFlag so that SystemExit doesn't call C exit()

    Without this flag, if code running in the interactive interpreter raises SystemExit, the interpreter will call the C exit() function, which will abort GRUB entirely. With Py_InspectFlag set, SystemExit will propagate like any other exception. This then allows calling modules intended as standalone programs and continuing afterward. Such calls may still want to catch SystemExit and provide a more user-friendly result than a traceback.

  • init: Time the import and initialization of modules

    In the process, always put timing start and end messages on separate lines, so that a message printed between them will not break the formatting.

  • efi: Add a safe event callback mechanism using Py_AddPendingCall

    Since event callbacks can occur asynchronously, use a C callback that invokes Py_AddPendingCall, rather than a Python ctypes callback.


  • efi: Add GUIDs for EFI networking protocols

  • efi: Make efi.show_available_protocols() show output with the pager

  • testacpi: Test that all CPUs return the same _PSS

  • acpi: AcpiGetTable functions don't need full ACPI init

    Just call the early tables-only initialization before running them.

  • python: Support compiling with Py_DEBUG; BITS does not enable Py_DEBUG by default, but this allows developers to enable it at build time for low-level Python debugging.

  • Provide file and line number for calls to abort(), to aid debugging

  • efi: Return ConfigurationTableDict as an OrderedDict

    The order of configuration tables can potentially matter, so preserve it.

  • Merge the acpica, smp, and bitsutil modules into the python module

    This will allow calls from the other modules into the python module, without creating a dependency cycle.

  • efi: Make efi.exit() invoke any Python atexit handlers before exiting. This provides an opportunity to clean up before exiting. Note that not all EFI resource allocations perform such cleanup yet.

  • efi: Add constants for key scancodes

  • efi: Add a general keyboard callback mechanism

    Call RegisterKeyNotify with a C callback that calls into Python; once in Python, dispatch to a specific Python handler based on the key.

  • efi: Add more known UUIDs from the UEFI specification

  • python: Implement time.sleep

    Implemented as a busyloop in Python, rather than calling into C. We want to allow for background processing (such as events or keyboard notify handlers), and we don't currently have any means of actually sleeping while doing so.

  • python: Add time.gmtime for compatibility

    Timezones intentionally ignored; always assumes localtime matches UTC.

  • python: Set sys.argv=[] by default for compatibility

    Stock python sets sys.argv even when running the interactive interpreter. Some Python test functions check for arguments but don't handle the case of sys.argv not existing at all. Set sys.argv to an empty list for compatibility.


  • Fix a bug on x86-64 EFI that would occasionally cause a libffi call or callback to malfunction (bad return value, abort(), or stack corruption and crash), due to an EFI interrupt corrupting data left in the red zone. Assembly functions in libffi's support for the x86-64 POSIX ABI (as used between BITS C and Python code, such as calls to ACPI) used the "red zone" defined by the ABI as scratch space; however, EFI firmware does not follow the same ABI, and an EFI interrupt can overwrite any data stored below the stack pointer. Thus, an interrupt that occurred during the small regions of assembly code relying on data in the red zone would cause rare, hard-to-debug issues.

    Fix these two libffi assembly routines (ffi_call_unix64 and ffi_closure_unix64) to not rely on the red zone remaining untouched while they run; adjust the stack pointer to contain all scratch space, and only access data above the stack pointer.

  • Disable GCC 5.2's new -Wdiscarded-array-qualifiers warning for GRUB

    GRUB uses -Werror, and the GRUB 2.00 snapshot we use doesn't satisfy this warning. Pass -Wno-discarded-array-qualifiers to configure to disable the warning.

  • testacpi: Fix typo in _MAT test

  • smbios: Fix field name typo

    This caused an exception when decoding a SystemEnclosure with contained elements.

  • testacpi: When testing ACPI _PSS, preserve the current pstate

    Introduce a new bits.preserve_msr() context manager to preserve an MSR on all CPUs around a block of code.

  • pstate: Preserve the current pstate around the hardware pstate test

  • Update URLs in documentation to https where available

  • efi: Save configuration tables to file decoded as GUID and pointer

  • Fix typos in PCIe error injection

  • Makefile: Fix a race condition between parallel grub install targets

    Occasionally, the grub install targets for two platforms would both try to install the same platform-independent script (e.g. grub-mkrescue) at the same time to the same location, generating a spurious failure saying the file already exists. Fix by installing the grub binaries for each platform to a separate temporary directory.

  • python: Fix line history navigation with Ctrl-O

    Ctrl-O on a line in history submits the line and causes the next call to readline to start with the following line from history. That initial state caused readline to not have a recorded state for the line "after" all existing history (what would be a fresh new blank line if Ctrl-O had not left the "vertical cursor" back in history). Subsequently navigating down to the end of history would then raise an exception.

    Fix that downward navigation to materialize a fresh new blank line when navigating down from the last line in history.