Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1#!/usr/bin/env python3
2# SPDX-License-Identifier: GPL-2.0+
3#
4# pylint: disable=C0103,C0209
5#
6#
7
8"""
9Interacts with the POSIX jobserver during the Kernel build time.
10
11A "normal" jobserver task, like the one initiated by a make subrocess would do:
12
13 - open read/write file descriptors to communicate with the job server;
14 - ask for one slot by calling:
15 claim = os.read(reader, 1)
16 - when the job finshes, call:
17 os.write(writer, b"+") # os.write(writer, claim)
18
19Here, the goal is different: This script aims to get the remaining number
20of slots available, using all of them to run a command which handle tasks in
21parallel. To to that, it has a loop that ends only after there are no
22slots left. It then increments the number by one, in order to allow a
23call equivalent to make -j$((claim+1)), e.g. having a parent make creating
24$claim child to do the actual work.
25
26The end goal here is to keep the total number of build tasks under the
27limit established by the initial make -j$n_proc call.
28
29See:
30 https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
31"""
32
33import errno
34import os
35import subprocess
36import sys
37
38class JobserverExec:
39 """
40 Claim all slots from make using POSIX Jobserver.
41
42 The main methods here are:
43 - open(): reserves all slots;
44 - close(): method returns all used slots back to make;
45 - run(): executes a command setting PARALLELISM=<available slots jobs + 1>
46 """
47
48 def __init__(self):
49 """Initialize internal vars"""
50 self.claim = 0
51 self.jobs = b""
52 self.reader = None
53 self.writer = None
54 self.is_open = False
55
56 def open(self):
57 """Reserve all available slots to be claimed later on"""
58
59 if self.is_open:
60 return
61
62 try:
63 # Fetch the make environment options.
64 flags = os.environ["MAKEFLAGS"]
65 # Look for "--jobserver=R,W"
66 # Note that GNU Make has used --jobserver-fds and --jobserver-auth
67 # so this handles all of them.
68 opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
69
70 # Parse out R,W file descriptor numbers and set them nonblocking.
71 # If the MAKEFLAGS variable contains multiple instances of the
72 # --jobserver-auth= option, the last one is relevant.
73 fds = opts[-1].split("=", 1)[1]
74
75 # Starting with GNU Make 4.4, named pipes are used for reader
76 # and writer.
77 # Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134
78 _, _, path = fds.partition("fifo:")
79
80 if path:
81 self.reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
82 self.writer = os.open(path, os.O_WRONLY)
83 else:
84 self.reader, self.writer = [int(x) for x in fds.split(",", 1)]
85 # Open a private copy of reader to avoid setting nonblocking
86 # on an unexpecting process with the same reader fd.
87 self.reader = os.open("/proc/self/fd/%d" % (self.reader),
88 os.O_RDONLY | os.O_NONBLOCK)
89
90 # Read out as many jobserver slots as possible
91 while True:
92 try:
93 slot = os.read(self.reader, 8)
94 self.jobs += slot
95 except (OSError, IOError) as e:
96 if e.errno == errno.EWOULDBLOCK:
97 # Stop at the end of the jobserver queue.
98 break
99 # If something went wrong, give back the jobs.
100 if self.jobs:
101 os.write(self.writer, self.jobs)
102 raise e
103
104 # Add a bump for our caller's reserveration, since we're just going
105 # to sit here blocked on our child.
106 self.claim = len(self.jobs) + 1
107
108 except (KeyError, IndexError, ValueError, OSError, IOError):
109 # Any missing environment strings or bad fds should result in just
110 # not being parallel.
111 self.claim = None
112
113 self.is_open = True
114
115 def close(self):
116 """Return all reserved slots to Jobserver"""
117
118 if not self.is_open:
119 return
120
121 # Return all the reserved slots.
122 if len(self.jobs):
123 os.write(self.writer, self.jobs)
124
125 self.is_open = False
126
127 def __enter__(self):
128 self.open()
129 return self
130
131 def __exit__(self, exc_type, exc_value, exc_traceback):
132 self.close()
133
134 def run(self, cmd, *args, **pwargs):
135 """
136 Run a command setting PARALLELISM env variable to the number of
137 available job slots (claim) + 1, e.g. it will reserve claim slots
138 to do the actual build work, plus one to monitor its children.
139 """
140 self.open() # Ensure that self.claim is set
141
142 # We can only claim parallelism if there was a jobserver (i.e. a
143 # top-level "-jN" argument) and there were no other failures. Otherwise
144 # leave out the environment variable and let the child figure out what
145 # is best.
146 if self.claim:
147 os.environ["PARALLELISM"] = str(self.claim)
148
149 return subprocess.call(cmd, *args, **pwargs)