e147db5233
Fixes "permission denied" return when are already process group / session leader. GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4678
70 lines
1.9 KiB
Go
70 lines
1.9 KiB
Go
// Copyright (C) 2018 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at https://mozilla.org/MPL/2.0/.
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package osutil
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import (
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"os"
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"syscall"
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"github.com/pkg/errors"
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)
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const ioprioClassShift = 13
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type ioprioClass int
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const (
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ioprioClassRT ioprioClass = iota + 1
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ioprioClassBE
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ioprioClassIdle
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)
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const (
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ioprioWhoProcess = iota + 1
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ioprioWhoPGRP
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ioprioWhoUser
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)
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func ioprioSet(class ioprioClass, value int) error {
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res, _, err := syscall.Syscall(syscall.SYS_IOPRIO_SET,
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uintptr(ioprioWhoProcess), 0,
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uintptr(class)<<ioprioClassShift|uintptr(value))
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if res == 0 {
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return nil
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}
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return err
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}
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// SetLowPriority lowers the process CPU scheduling priority, and possibly
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// I/O priority depending on the platform and OS.
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func SetLowPriority() error {
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// Move ourselves to a new process group so that we can use the process
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// group variants of Setpriority etc to affect all of our threads in one
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// go. If this fails, bail, so that we don't affect things we shouldn't.
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// If we are already the leader of our own process group, do nothing.
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if pgid, err := syscall.Getpgid(0); err != nil {
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// This error really shouldn't happen
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return errors.Wrap(err, "get process group")
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} else if pgid != os.Getpid() {
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// We are not process group leader. Elevate!
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if err := syscall.Setpgid(0, 0); err != nil {
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return errors.Wrap(err, "set process group")
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}
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}
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// Process zero is "self", niceness value 9 is something between 0
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// (default) and 19 (worst priority).
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if err := syscall.Setpriority(syscall.PRIO_PGRP, 0, 9); err != nil {
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return errors.Wrap(err, "set niceness")
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}
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// Best effort, somewhere to the end of the scale (0 through 7 being the
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// range).
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err := ioprioSet(ioprioClassBE, 5)
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return errors.Wrap(err, "set I/O priority") // wraps nil as nil
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}
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