[PATCH v8 01/24] scripts/jobserver-exec: move the code to a class

Mauro Carvalho Chehab
2025-09-18T11:55:06Z

Convert the code inside jobserver-exec to a class and
properly document it.

Using a class allows reusing the jobserver logic on other
scripts.

While the main code remains unchanged, being compatible with
Python 2.6 and 3.0+, its coding style now follows a more
modern standard, having tabs replaced by a 4-spaces
indent, passing autopep8, black and pylint.

The code allows using a pythonic way to enter/exit a python
code, e.g. it now supports:

with JobserverExec() as jobserver:
jobserver.run(sys.argv[1:])

With the new code, the __exit__() function should ensure
that the jobserver slot will be closed at the end, even if
something bad happens somewhere.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
---
scripts/jobserver-exec | 218 ++++++++++++++++++++++++++++-------------
1 file changed, 151 insertions(+), 67 deletions(-)

diff --git a/scripts/jobserver-exec b/scripts/jobserver-exec
index 7eca035472d3..897c0cca9e6e 100755
--- a/scripts/jobserver-exec
+++ b/scripts/jobserver-exec
@@ -1,77 +1,161 @@
#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-2.0+
#
+# pylint: disable=C0103,C0209
+#
# This determines how many parallel tasks "make" is expecting, as it is
# not exposed via an special variables, reserves them all, runs a subprocess
# with PARALLELISM environment variable set, and releases the jobs back again.
#
# https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
-from __future__ import print_function
-import os, sys, errno
+
+"""
+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 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.
+"""
+
+import errno
+import os
import subprocess
+import sys

-# Extract and prepare jobserver file descriptors from environment.
-claim = 0
-jobs = b""
-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:
- reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
- writer = os.open(path, os.O_WRONLY)
- else:
- reader, 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.
- reader = os.open("/proc/self/fd/%d" % (reader),
- os.O_RDONLY | os.O_NONBLOCK)
-
- # Read out as many jobserver slots as possible.
- while True:
- try:
- slot = os.read(reader, 8)
- 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 len(jobs):
- os.write(writer, jobs)
- raise e
- # Add a bump for our caller's reserveration, since we're just going
- # to sit here blocked on our child.
- claim = len(jobs) + 1
-except (KeyError, IndexError, ValueError, OSError, IOError) as e:
- # Any missing environment strings or bad fds should result in just
- # not being parallel.
- pass
-
-# 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 claim > 0:
- os.environ['PARALLELISM'] = '%d' % (claim)
-
-rc = subprocess.call(sys.argv[1:])
-
-# Return all the reserved slots.
-if len(jobs):
- os.write(writer, jobs)
-
-sys.exit(rc)
+
+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):
+ """
+ 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)
+
+
+def main():
+ """Main program"""
+ with JobserverExec() as jobserver:
+ jobserver.run(sys.argv[1:])
+
+
+if __name__ == "__main__":
+ main()
--
2.51.0