projects/linux·blob master · refs

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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 subprocess would do:
12
13 - open read/write file descriptors to communicate with the job server;
14 - ask for one slot by calling::
15
16 claim = os.read(reader, 1)
17
18 - when the job finishes, call::
19
20 os.write(writer, b"+") # os.write(writer, claim)
21
22Here, the goal is different: This script aims to get the remaining number
23of slots available, using all of them to run a command which handle tasks in
24parallel. To to that, it has a loop that ends only after there are no
25slots left. It then increments the number by one, in order to allow a
26call equivalent to ``make -j$((claim+1))``, e.g. having a parent make creating
27$claim child to do the actual work.
28
29The end goal here is to keep the total number of build tasks under the
30limit established by the initial ``make -j$n_proc`` call.
31
32See:
33 https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
34"""
35
36import errno
37import os
38import subprocess
39import sys
40
41def warn(text, *args):
42 print(f'WARNING: {text}', *args, file = sys.stderr)
43
44class JobserverExec:
45 """
46 Claim all slots from make using POSIX Jobserver.
47
48 The main methods here are:
49
50 - open(): reserves all slots;
51 - close(): method returns all used slots back to make;
52 - run(): executes a command setting PARALLELISM=<available slots jobs + 1>.
53 """
54
55 def __init__(self):
56 """Initialize internal vars."""
57 self.claim = 0
58 self.jobs = b""
59 self.reader = None
60 self.writer = None
61 self.is_open = False
62
63 def open(self):
64 """Reserve all available slots to be claimed later on."""
65
66 if self.is_open:
67 return
68 self.is_open = True # We only try once
69 self.claim = None
70 #
71 # Check the make flags for "--jobserver=R,W"
72 # Note that GNU Make has used --jobserver-fds and --jobserver-auth
73 # so this handles all of them.
74 #
75 flags = os.environ.get('MAKEFLAGS', '')
76 opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
77 if not opts:
78 return
79 #
80 # Separate out the provided file descriptors
81 #
82 split_opt = opts[-1].split('=', 1)
83 if len(split_opt) != 2:
84 warn('unparseable option:', opts[-1])
85 return
86 fds = split_opt[1]
87 #
88 # As of GNU Make 4.4, we'll be looking for a named pipe
89 # identified as fifo:path
90 #
91 if fds.startswith('fifo:'):
92 path = fds[len('fifo:'):]
93 try:
94 self.reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
95 self.writer = os.open(path, os.O_WRONLY)
96 except (OSError, IOError):
97 warn('unable to open jobserver pipe', path)
98 return
99 #
100 # Otherwise look for integer file-descriptor numbers.
101 #
102 else:
103 split_fds = fds.split(',')
104 if len(split_fds) != 2:
105 warn('malformed jobserver file descriptors:', fds)
106 return
107 try:
108 self.reader = int(split_fds[0])
109 self.writer = int(split_fds[1])
110 except ValueError:
111 warn('non-integer jobserver file-descriptors:', fds)
112 return
113 try:
114 #
115 # Open a private copy of reader to avoid setting nonblocking
116 # on an unexpecting process with the same reader fd.
117 #
118 self.reader = os.open(f"/proc/self/fd/{self.reader}",
119 os.O_RDONLY | os.O_NONBLOCK)
120 except (IOError, OSError) as e:
121 warn('Unable to reopen jobserver read-side pipe:', repr(e))
122 return
123 #
124 # OK, we have the channel to the job server; read out as many jobserver
125 # slots as possible.
126 #
127 while True:
128 try:
129 slot = os.read(self.reader, 8)
130 if not slot:
131 #
132 # Something went wrong. Clear self.jobs to avoid writing
133 # weirdness back to the jobserver and give up.
134 self.jobs = b""
135 warn("unexpected empty token from jobserver;"
136 " possible invalid '--jobserver-auth=' setting")
137 self.claim = None
138 return
139 except (OSError, IOError) as e:
140 #
141 # If there is nothing more to read then we are done.
142 #
143 if e.errno == errno.EWOULDBLOCK:
144 break
145 #
146 # Anything else says that something went weird; give back
147 # the jobs and give up.
148 #
149 if self.jobs:
150 os.write(self.writer, self.jobs)
151 self.claim = None
152 warn('error reading from jobserver pipe', repr(e))
153 return
154 self.jobs += slot
155 #
156 # Add a bump for our caller's reserveration, since we're just going
157 # to sit here blocked on our child.
158 #
159 self.claim = len(self.jobs) + 1
160
161 def close(self):
162 """Return all reserved slots to Jobserver."""
163
164 if not self.is_open:
165 return
166
167 # Return all the reserved slots.
168 if len(self.jobs):
169 os.write(self.writer, self.jobs)
170
171 self.is_open = False
172
173 def __enter__(self):
174 self.open()
175 return self
176
177 def __exit__(self, exc_type, exc_value, exc_traceback):
178 self.close()
179
180 def run(self, cmd, *args, **pwargs):
181 """
182 Run a command setting PARALLELISM env variable to the number of
183 available job slots (claim) + 1, e.g. it will reserve claim slots
184 to do the actual build work, plus one to monitor its children.
185 """
186 self.open() # Ensure that self.claim is set
187
188 # We can only claim parallelism if there was a jobserver (i.e. a
189 # top-level "-jN" argument) and there were no other failures. Otherwise
190 # leave out the environment variable and let the child figure out what
191 # is best.
192 if self.claim:
193 os.environ["PARALLELISM"] = str(self.claim)
194
195 return subprocess.call(cmd, *args, **pwargs)