| #!/usr/bin/env python3 | |
| # SPDX-License-Identifier: GPL-2.0+ | |
| # | |
| # pylint: disable=C0103,C0209 | |
| # | |
| # | |
| """ | |
| Interacts with the POSIX jobserver during the Kernel build time. | |
| A "normal" jobserver task, like the one initiated by a make subprocess would do: | |
| - open read/write file descriptors to communicate with the job server; | |
| - ask for one slot by calling:: | |
| claim = os.read(reader, 1) | |
| - when the job finishes, call:: | |
| os.write(writer, b"+") # os.write(writer, claim) | |
| Here, the goal is different: This script aims to get the remaining number | |
| of slots available, using all of them to run a command which handle tasks in | |
| parallel. To to that, it has a loop that ends only after there are no | |
| slots left. It then increments the number by one, in order to allow a | |
| call equivalent to ``make -j$((claim+1))``, e.g. having a parent make creating | |
| $claim child to do the actual work. | |
| The end goal here is to keep the total number of build tasks under the | |
| limit established by the initial ``make -j$n_proc`` call. | |
| See: | |
| https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver | |
| """ | |
| import errno | |
| import os | |
| import subprocess | |
| import sys | |
| def warn(text, *args): | |
| print(f'WARNING: {text}', *args, file = sys.stderr) | |
| class JobserverExec: | |
| """ | |
| Claim all slots from make using POSIX Jobserver. | |
| The main methods here are: | |
| - open(): reserves all slots; | |
| - close(): method returns all used slots back to make; | |
| - run(): executes a command setting PARALLELISM=<available slots jobs + 1>. | |
| """ | |
| def __init__(self): | |
| """Initialize internal vars.""" | |
| self.claim = 0 | |
| self.jobs = b"" | |
| self.reader = None | |
| self.writer = None | |
| self.is_open = False | |
| def open(self): | |
| """Reserve all available slots to be claimed later on.""" | |
| if self.is_open: | |
| return | |
| self.is_open = True # We only try once | |
| self.claim = None | |
| # | |
| # Check the make flags for "--jobserver=R,W" | |
| # Note that GNU Make has used --jobserver-fds and --jobserver-auth | |
| # so this handles all of them. | |
| # | |
| flags = os.environ.get('MAKEFLAGS', '') | |
| opts = [x for x in flags.split(" ") if x.startswith("--jobserver")] | |
| if not opts: | |
| return | |
| # | |
| # Separate out the provided file descriptors | |
| # | |
| split_opt = opts[-1].split('=', 1) | |
| if len(split_opt) != 2: | |
| warn('unparseable option:', opts[-1]) | |
| return | |
| fds = split_opt[1] | |
| # | |
| # As of GNU Make 4.4, we'll be looking for a named pipe | |
| # identified as fifo:path | |
| # | |
| if fds.startswith('fifo:'): | |
| path = fds[len('fifo:'):] | |
| try: | |
| self.reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK) | |
| self.writer = os.open(path, os.O_WRONLY) | |
| except (OSError, IOError): | |
| warn('unable to open jobserver pipe', path) | |
| return | |
| # | |
| # Otherwise look for integer file-descriptor numbers. | |
| # | |
| else: | |
| split_fds = fds.split(',') | |
| if len(split_fds) != 2: | |
| warn('malformed jobserver file descriptors:', fds) | |
| return | |
| try: | |
| self.reader = int(split_fds[0]) | |
| self.writer = int(split_fds[1]) | |
| except ValueError: | |
| warn('non-integer jobserver file-descriptors:', fds) | |
| return | |
| try: | |
| # | |
| # Open a private copy of reader to avoid setting nonblocking | |
| # on an unexpecting process with the same reader fd. | |
| # | |
| self.reader = os.open(f"/proc/self/fd/{self.reader}", | |
| os.O_RDONLY | os.O_NONBLOCK) | |
| except (IOError, OSError) as e: | |
| warn('Unable to reopen jobserver read-side pipe:', repr(e)) | |
| return | |
| # | |
| # OK, we have the channel to the job server; read out as many jobserver | |
| # slots as possible. | |
| # | |
| while True: | |
| try: | |
| slot = os.read(self.reader, 8) | |
| if not slot: | |
| # | |
| # Something went wrong. Clear self.jobs to avoid writing | |
| # weirdness back to the jobserver and give up. | |
| self.jobs = b"" | |
| warn("unexpected empty token from jobserver;" | |
| " possible invalid '--jobserver-auth=' setting") | |
| self.claim = None | |
| return | |
| except (OSError, IOError) as e: | |
| # | |
| # If there is nothing more to read then we are done. | |
| # | |
| if e.errno == errno.EWOULDBLOCK: | |
| break | |
| # | |
| # Anything else says that something went weird; give back | |
| # the jobs and give up. | |
| # | |
| if self.jobs: | |
| os.write(self.writer, self.jobs) | |
| self.claim = None | |
| warn('error reading from jobserver pipe', repr(e)) | |
| return | |
| self.jobs += slot | |
| # | |
| # Add a bump for our caller's reserveration, since we're just going | |
| # to sit here blocked on our child. | |
| # | |
| self.claim = len(self.jobs) + 1 | |
| def close(self): | |
| """Return all reserved slots to Jobserver.""" | |
| if not self.is_open: | |
| return | |
| # Return all the reserved slots. | |
| if len(self.jobs): | |
| os.write(self.writer, self.jobs) | |
| self.is_open = False | |
| def __enter__(self): | |
| self.open() | |
| return self | |
| def __exit__(self, exc_type, exc_value, exc_traceback): | |
| self.close() | |
| def run(self, cmd, *args, **pwargs): | |
| """ | |
| Run a command setting PARALLELISM env variable to the number of | |
| available job slots (claim) + 1, e.g. it will reserve claim slots | |
| to do the actual build work, plus one to monitor its children. | |
| """ | |
| self.open() # Ensure that self.claim is set | |
| # We can only claim parallelism if there was a jobserver (i.e. a | |
| # top-level "-jN" argument) and there were no other failures. Otherwise | |
| # leave out the environment variable and let the child figure out what | |
| # is best. | |
| if self.claim: | |
| os.environ["PARALLELISM"] = str(self.claim) | |
| return subprocess.call(cmd, *args, **pwargs) |