blob: a47cba3e43a4daffb78eacce733d55e86e525d21 [file] [log] [blame]
// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/posix/can_lower_nice_to.h"
#include <limits.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <unistd.h>
#include "build/build_config.h"
#include "starboard/types.h"
// Not defined on AIX by default.
#if defined(OS_AIX)
#if defined(RLIMIT_NICE)
#error Assumption about OS_AIX is incorrect
#define RLIMIT_NICE 20
namespace base {
namespace internal {
bool CanLowerNiceTo(int nice_value) {
// On a POSIX system, the nice value of a thread can be lowered 1. by the root
// user, 2. by a user with the CAP_SYS_NICE permission or 3. by any user if
// the target value is within the range allowed by RLIMIT_NICE.
// 1. Check for root user.
if (geteuid() == 0)
return true;
// 2. Skip checking the CAP_SYS_NICE permission because it would require
// 3. Check whether the target value is within the range allowed by
// NZERO should be defined in <limits.h> per POSIX, and should be at least 20.
// (NZERO-1) is the highest possible niceness value (i.e. lowest priority).
// Most platforms use NZERO=20.
// RLIMIT_NICE tells us how much we can reduce niceness (increase priority) if
// we start at NZERO. For example, if NZERO is 20 and the rlimit is 30, we can
// lower niceness anywhere within the [-10, 19] range (20 - 30 = -10).
// So, we are allowed to reduce niceness to a minimum of NZERO - rlimit:
struct rlimit rlim;
if (getrlimit(RLIMIT_NICE, &rlim) != 0)
return false;
const int lowest_nice_allowed = NZERO - static_cast<int>(rlim.rlim_cur);
// And lowering niceness to |nice_value| is allowed if it is greater than or
// equal to the limit:
return nice_value >= lowest_nice_allowed;
} // namespace internal
} // namespace base