#!/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 subrocess 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 finshes, call:        os.write(writer, b"+")  # os.write(writer, claim) Here, the goal is different: This script aims to get the remaining numberof slots available, using all of them to run a command which handle tasks inparallel. To to that, it has a loop that ends only after there are noslots left. It then increments the number by one, in order to allow acall 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 thelimit 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 errnoimport osimport subprocessimport sys 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         try:            # Fetch the make environment options.            flags = os.environ["MAKEFLAGS"]            # Look for "--jobserver=R,W"            # Note that GNU Make has used --jobserver-fds and --jobserver-auth            # so this handles all of them.            opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]             # Parse out R,W file descriptor numbers and set them nonblocking.            # If the MAKEFLAGS variable contains multiple instances of the            # --jobserver-auth= option, the last one is relevant.            fds = opts[-1].split("=", 1)[1]             # Starting with GNU Make 4.4, named pipes are used for reader            # and writer.            # Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134            _, _, path = fds.partition("fifo:")             if path:                self.reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)                self.writer = os.open(path, os.O_WRONLY)            else:                self.reader, self.writer = [int(x) for x in fds.split(",", 1)]                # Open a private copy of reader to avoid setting nonblocking                # on an unexpecting process with the same reader fd.                self.reader = os.open("/proc/self/fd/%d" % (self.reader),                                      os.O_RDONLY | os.O_NONBLOCK)             # Read out as many jobserver slots as possible            while True:                try:                    slot = os.read(self.reader, 8)                    self.jobs += slot                except (OSError, IOError) as e:                    if e.errno == errno.EWOULDBLOCK:                        # Stop at the end of the jobserver queue.                        break                    # If something went wrong, give back the jobs.                    if self.jobs:                        os.write(self.writer, self.jobs)                    raise e             # 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         except (KeyError, IndexError, ValueError, OSError, IOError):            # Any missing environment strings or bad fds should result in just            # not being parallel.            self.claim = None         self.is_open = True     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)