61 lines
1.9 KiB
C++
61 lines
1.9 KiB
C++
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// Copyright 2018 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/posix/can_lower_nice_to.h"
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#include <limits.h>
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#include <sys/resource.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include "build/build_config.h"
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// Not defined on AIX by default.
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#if defined(OS_AIX)
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#if defined(RLIMIT_NICE)
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#error Assumption about OS_AIX is incorrect
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#endif
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#define RLIMIT_NICE 20
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#endif
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namespace base {
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namespace internal {
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bool CanLowerNiceTo(int nice_value) {
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// On a POSIX system, the nice value of a thread can be lowered 1. by the root
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// user, 2. by a user with the CAP_SYS_NICE permission or 3. by any user if
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// the target value is within the range allowed by RLIMIT_NICE.
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// 1. Check for root user.
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if (geteuid() == 0)
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return true;
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// 2. Skip checking the CAP_SYS_NICE permission because it would require
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// libcap.so.
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// 3. Check whether the target value is within the range allowed by
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// RLIMIT_NICE.
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//
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// NZERO should be defined in <limits.h> per POSIX, and should be at least 20.
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// (NZERO-1) is the highest possible niceness value (i.e. lowest priority).
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// Most platforms use NZERO=20.
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//
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// RLIMIT_NICE tells us how much we can reduce niceness (increase priority) if
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// we start at NZERO. For example, if NZERO is 20 and the rlimit is 30, we can
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// lower niceness anywhere within the [-10, 19] range (20 - 30 = -10).
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//
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// So, we are allowed to reduce niceness to a minimum of NZERO - rlimit:
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struct rlimit rlim;
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if (getrlimit(RLIMIT_NICE, &rlim) != 0)
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return false;
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const int lowest_nice_allowed = NZERO - static_cast<int>(rlim.rlim_cur);
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// And lowering niceness to |nice_value| is allowed if it is greater than or
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// equal to the limit:
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return nice_value >= lowest_nice_allowed;
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}
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} // namespace internal
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} // namespace base
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