docs, parallelism: Do not leak blocking mode to other readers (dffd0114) · Commits · 戴 / test

Setting non-blocking via a local copy of the jobserver file descriptor is safer than just assuming other reader processes with the same fd open are prepared for it to be non-blocking. Suggested-by:

Rasmus Villemoes <linux@rasmusvillemoes.dk> Link: https://lore.kernel.org/lkml/44c01043-ab24-b4de-6544-e8efd153e27a@rasmusvillemoes.dk Signed-off-by:

Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20191121205929.40371-3-keescook@chromium.org Signed-off-by:

Jonathan Corbet <corbet@lwn.net>

scripts/jobserver-count

+6 −8

Original line number	Diff line number	Diff line
		@@ -12,12 +12,6 @@ default="1"
		if len(sys.argv) > 1:
		default=sys.argv[1]

		# Set non-blocking for a given file descriptor.
		def nonblock(fd):
		flags = fcntl.fcntl(fd, fcntl.F_GETFL)
		fcntl.fcntl(fd, fcntl.F_SETFL, flags \| os.O_NONBLOCK)
		return fd

		# Extract and prepare jobserver file descriptors from envirnoment.
		try:
		# Fetch the make environment options.
		@@ -31,8 +25,12 @@ try:
		# Parse out R,W file descriptor numbers and set them nonblocking.
		fds = opts[0].split("=", 1)[1]
		reader, writer = [int(x) for x in fds.split(",", 1)]
		reader = nonblock(reader)
		except (KeyError, IndexError, ValueError, IOError):
		# 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)
		except (KeyError, IndexError, ValueError, IOError, OSError) as e:
		print(e, file=sys.stderr)
		# Any missing environment strings or bad fds should result in just
		# using the default specified parallelism.
		print(default)

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