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base.go
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// Copyright 2021 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package cgroupfs
import (
"bytes"
"fmt"
"sort"
"strconv"
"strings"
"github.com/MerlinKodo/gvisor/pkg/abi/linux"
"github.com/MerlinKodo/gvisor/pkg/context"
"github.com/MerlinKodo/gvisor/pkg/errors/linuxerr"
"github.com/MerlinKodo/gvisor/pkg/hostarch"
"github.com/MerlinKodo/gvisor/pkg/log"
"github.com/MerlinKodo/gvisor/pkg/sentry/fsimpl/kernfs"
"github.com/MerlinKodo/gvisor/pkg/sentry/kernel"
"github.com/MerlinKodo/gvisor/pkg/sentry/kernel/auth"
"github.com/MerlinKodo/gvisor/pkg/sentry/vfs"
"github.com/MerlinKodo/gvisor/pkg/usermem"
)
// controllerCommon implements kernel.CgroupController.
//
// Must call init before use.
//
// +stateify savable
type controllerCommon struct {
ty kernel.CgroupControllerType
fs *filesystem
// parent is the parent controller if any. Immutable.
//
// Note that we don't have to update this on renames, since cgroup
// directories can't be moved to a different parent directory.
parent controller
}
func (c *controllerCommon) init(ty kernel.CgroupControllerType, fs *filesystem) {
c.ty = ty
c.fs = fs
}
func (c *controllerCommon) cloneFromParent(parent controller) {
c.ty = parent.Type()
c.fs = parent.Filesystem()
c.parent = parent
}
// Filesystem implements controller.Filesystem.
func (c *controllerCommon) Filesystem() *filesystem {
return c.fs
}
// Type implements kernel.CgroupController.Type.
func (c *controllerCommon) Type() kernel.CgroupControllerType {
return kernel.CgroupControllerType(c.ty)
}
// HierarchyID implements kernel.CgroupController.HierarchyID.
func (c *controllerCommon) HierarchyID() uint32 {
return c.fs.hierarchyID
}
// NumCgroups implements kernel.CgroupController.NumCgroups.
func (c *controllerCommon) NumCgroups() uint64 {
return c.fs.numCgroups.Load()
}
// Enabled implements kernel.CgroupController.Enabled.
//
// Controllers are currently always enabled.
func (c *controllerCommon) Enabled() bool {
return true
}
// EffectiveRootCgroup implements kernel.CgroupController.EffectiveRootCgroup.
func (c *controllerCommon) EffectiveRootCgroup() kernel.Cgroup {
return c.fs.effectiveRootCgroup()
}
// controller is an interface for common functionality related to all cgroups.
// It is an extension of the public cgroup interface, containing cgroup
// functionality private to cgroupfs.
type controller interface {
kernel.CgroupController
// Filesystem returns the cgroupfs filesystem backing this controller.
Filesystem() *filesystem
// Clone creates a new controller based on the internal state of this
// controller. This is used to initialize a sub-cgroup based on the state of
// the parent.
Clone() controller
// AddControlFiles should extend the contents map with inodes representing
// control files defined by this controller.
AddControlFiles(ctx context.Context, creds *auth.Credentials, c *cgroupInode, contents map[string]kernfs.Inode)
// Enter is called when a task initially moves into a cgroup. This is
// distinct from migration because the task isn't migrating away from a
// cgroup. Enter is called when a task is created and joins its initial
// cgroup, or when cgroupfs is mounted and existing tasks are moved into
// cgroups.
Enter(t *kernel.Task)
// Leave is called when a task leaves a cgroup. This is distinct from
// migration because the task isn't migrating to another cgroup. Leave is
// called when a task exits.
Leave(t *kernel.Task)
// PrepareMigrate signals the controller that a migration is about to
// happen. The controller should check for any conditions that would prevent
// the migration. If PrepareMigrate succeeds, the controller must
// unconditionally either accept the migration via CommitMigrate, or roll it
// back via AbortMigrate.
//
// Postcondition: If PrepareMigrate returns nil, caller must resolve the
// migration by calling either CommitMigrate or AbortMigrate.
PrepareMigrate(t *kernel.Task, src controller) error
// CommitMigrate completes an in-flight migration.
//
// Precondition: Caller must call a corresponding PrepareMigrate.
CommitMigrate(t *kernel.Task, src controller)
// AbortMigrate cancels an in-flight migration.
//
// Precondition: Caller must call a corresponding PrepareMigrate.
AbortMigrate(t *kernel.Task, src controller)
// Charge charges a controller for a particular resource. The implementation
// should panic if passed a resource type they do not control.
Charge(t *kernel.Task, d *kernfs.Dentry, res kernel.CgroupResourceType, value int64) error
}
// cgroupInode implements kernel.CgroupImpl and kernfs.Inode.
//
// +stateify savable
type cgroupInode struct {
dir
// id is the id of this cgroup.
id uint32
// controllers is the set of controllers for this cgroup. This is used to
// store controller-specific state per cgroup. The set of controllers should
// match the controllers for this hierarchy as tracked by the filesystem
// object. Immutable.
controllers map[kernel.CgroupControllerType]controller
// ts is the list of tasks in this cgroup. The kernel is responsible for
// removing tasks from this list before they're destroyed, so any tasks on
// this list are always valid.
//
// ts, and cgroup membership in general is protected by fs.tasksMu.
ts map[*kernel.Task]struct{}
}
var _ kernel.CgroupImpl = (*cgroupInode)(nil)
func (fs *filesystem) newCgroupInode(ctx context.Context, creds *auth.Credentials, parent *cgroupInode, mode linux.FileMode) kernfs.Inode {
c := &cgroupInode{
dir: dir{fs: fs},
ts: make(map[*kernel.Task]struct{}),
controllers: make(map[kernel.CgroupControllerType]controller),
}
c.dir.cgi = c
k := kernel.KernelFromContext(ctx)
r := k.CgroupRegistry()
// Assign id for the cgroup.
cid, err := r.NextCgroupID()
if err != nil {
log.Warningf("cgroupfs newCgroupInode: Failed to assign id to the cgroup: %v", err)
}
c.id = cid
r.AddCgroup(c)
contents := make(map[string]kernfs.Inode)
contents["cgroup.procs"] = fs.newControllerWritableFile(ctx, creds, &cgroupProcsData{c}, false)
contents["tasks"] = fs.newControllerWritableFile(ctx, creds, &tasksData{c}, false)
if parent != nil {
for ty, ctl := range parent.controllers {
new := ctl.Clone()
c.controllers[ty] = new
new.AddControlFiles(ctx, creds, c, contents)
}
} else {
for _, ctl := range fs.controllers {
// Uniqueness of controllers enforced by the filesystem on
// creation. The root cgroup uses the controllers directly from the
// filesystem.
c.controllers[ctl.Type()] = ctl
ctl.AddControlFiles(ctx, creds, c, contents)
}
}
c.dir.InodeAttrs.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), mode)
c.dir.OrderedChildren.Init(kernfs.OrderedChildrenOptions{Writable: true})
c.dir.IncLinks(c.dir.OrderedChildren.Populate(contents))
fs.numCgroups.Add(1)
return c
}
// HierarchyID implements kernel.CgroupImpl.HierarchyID.
func (c *cgroupInode) HierarchyID() uint32 {
return c.fs.hierarchyID
}
// Name implements kernel.CgroupImpl.Name.
func (c *cgroupInode) Name() string {
return c.fs.hierarchyName
}
// Controllers implements kernel.CgroupImpl.Controllers.
func (c *cgroupInode) Controllers() []kernel.CgroupController {
return c.fs.kcontrollers
}
// tasks returns a snapshot of the tasks inside the cgroup.
func (c *cgroupInode) tasks() []*kernel.Task {
c.fs.tasksMu.RLock()
defer c.fs.tasksMu.RUnlock()
ts := make([]*kernel.Task, 0, len(c.ts))
for t := range c.ts {
ts = append(ts, t)
}
return ts
}
// Enter implements kernel.CgroupImpl.Enter.
func (c *cgroupInode) Enter(t *kernel.Task) {
c.fs.tasksMu.Lock()
defer c.fs.tasksMu.Unlock()
c.ts[t] = struct{}{}
for _, ctl := range c.controllers {
ctl.Enter(t)
}
}
// Leave implements kernel.CgroupImpl.Leave.
func (c *cgroupInode) Leave(t *kernel.Task) {
c.fs.tasksMu.Lock()
defer c.fs.tasksMu.Unlock()
for _, ctl := range c.controllers {
ctl.Leave(t)
}
delete(c.ts, t)
}
// PrepareMigrate implements kernel.CgroupImpl.PrepareMigrate.
func (c *cgroupInode) PrepareMigrate(t *kernel.Task, src *kernel.Cgroup) error {
prepared := make([]controller, 0, len(c.controllers))
rollback := func() {
for _, p := range prepared {
c.controllers[p.Type()].AbortMigrate(t, p)
}
}
for srcType, srcCtl := range src.CgroupImpl.(*cgroupInode).controllers {
ctl := c.controllers[srcType]
if err := ctl.PrepareMigrate(t, srcCtl); err != nil {
rollback()
return err
}
prepared = append(prepared, srcCtl)
}
return nil
}
// CommitMigrate implements kernel.CgroupImpl.CommitMigrate.
func (c *cgroupInode) CommitMigrate(t *kernel.Task, src *kernel.Cgroup) {
c.fs.tasksMu.Lock()
defer c.fs.tasksMu.Unlock()
for srcType, srcCtl := range src.CgroupImpl.(*cgroupInode).controllers {
c.controllers[srcType].CommitMigrate(t, srcCtl)
}
srcI := src.CgroupImpl.(*cgroupInode)
delete(srcI.ts, t)
c.ts[t] = struct{}{}
}
// AbortMigrate implements kernel.CgroupImpl.AbortMigrate.
func (c *cgroupInode) AbortMigrate(t *kernel.Task, src *kernel.Cgroup) {
for srcType, srcCtl := range src.CgroupImpl.(*cgroupInode).controllers {
c.controllers[srcType].AbortMigrate(t, srcCtl)
}
}
// CgroupFromControlFileFD returns a cgroup object given a control file FD for the cgroup.
func (c *cgroupInode) CgroupFromControlFileFD(fd *vfs.FileDescription) kernel.Cgroup {
controlFileDentry := fd.Dentry().Impl().(*kernfs.Dentry)
// The returned parent dentry remains valid without holding locks because in
// cgroupfs, the parent directory relationship of a control file is
// effectively immutable. Control files cannot be unlinked, renamed or
// destroyed independently from their parent directory.
parentD := controlFileDentry.Parent()
return kernel.Cgroup{
Dentry: parentD,
CgroupImpl: c,
}
}
// Charge implements kernel.CgroupImpl.Charge.
//
// Charge notifies a matching controller of a change in resource usage. Due to
// the uniqueness of controllers, at most one controller will match. If no
// matching controller is present in this directory, the call silently
// succeeds. The caller should call Charge on all hierarchies to ensure any
// matching controller across the entire system is charged.
func (c *cgroupInode) Charge(t *kernel.Task, d *kernfs.Dentry, ctlType kernel.CgroupControllerType, res kernel.CgroupResourceType, value int64) error {
c.fs.tasksMu.RLock()
defer c.fs.tasksMu.RUnlock()
if ctl, ok := c.controllers[ctlType]; ok {
return ctl.Charge(t, d, res, value)
}
return nil
}
// ReadControl implements kernel.CgroupImpl.ReadControl.
func (c *cgroupInode) ReadControl(ctx context.Context, name string) (string, error) {
cfi, err := c.Lookup(ctx, name)
if err != nil {
return "", fmt.Errorf("no such control file")
}
cbf, ok := cfi.(controllerFileImpl)
if !ok {
return "", fmt.Errorf("no such control file")
}
if !cbf.AllowBackgroundAccess() {
return "", fmt.Errorf("this control may not be accessed from a background context")
}
var buf bytes.Buffer
err = cbf.Source().Data().Generate(ctx, &buf)
return buf.String(), err
}
// WriteControl implements kernel.CgroupImpl.WriteControl.
func (c *cgroupInode) WriteControl(ctx context.Context, name string, value string) error {
cfi, err := c.Lookup(ctx, name)
if err != nil {
return fmt.Errorf("no such control file")
}
// Do the more general cast first so we can give a meaningful error message when
// the control file exists, but isn't accessible (either due to being
// unwritable, or not being available from a background context).
cbf, ok := cfi.(controllerFileImpl)
if !ok {
return fmt.Errorf("no such control file")
}
if !cbf.AllowBackgroundAccess() {
return fmt.Errorf("this control may not be accessed from a background context")
}
wcbf, ok := cfi.(writableControllerFileImpl)
if !ok {
return fmt.Errorf("control file not writable")
}
ioSeq := usermem.BytesIOSequence([]byte(value))
n, err := wcbf.WriteBackground(ctx, ioSeq)
if err != nil {
return err
}
if n != int64(len(value)) {
return fmt.Errorf("short write")
}
return nil
}
// ID implements kernel.CgroupImpl.ID.
func (c *cgroupInode) ID() uint32 {
return c.id
}
func sortTIDs(tids []kernel.ThreadID) {
sort.Slice(tids, func(i, j int) bool { return tids[i] < tids[j] })
}
// +stateify savable
type cgroupProcsData struct {
*cgroupInode
}
// Generate implements vfs.DynamicBytesSource.Generate.
func (d *cgroupProcsData) Generate(ctx context.Context, buf *bytes.Buffer) error {
t := kernel.TaskFromContext(ctx)
currPidns := t.ThreadGroup().PIDNamespace()
pgids := make(map[kernel.ThreadID]struct{})
for _, task := range d.tasks() {
// Map dedups pgid, since iterating over all tasks produces multiple
// entries for the group leaders.
if pgid := currPidns.IDOfThreadGroup(task.ThreadGroup()); pgid != 0 {
pgids[pgid] = struct{}{}
}
}
pgidList := make([]kernel.ThreadID, 0, len(pgids))
for pgid := range pgids {
pgidList = append(pgidList, pgid)
}
sortTIDs(pgidList)
for _, pgid := range pgidList {
fmt.Fprintf(buf, "%d\n", pgid)
}
return nil
}
// Write implements vfs.WritableDynamicBytesSource.Write.
func (d *cgroupProcsData) Write(ctx context.Context, fd *vfs.FileDescription, src usermem.IOSequence, offset int64) (int64, error) {
tgid, n, err := parseInt64FromString(ctx, src)
if err != nil {
return n, err
}
t := kernel.TaskFromContext(ctx)
currPidns := t.ThreadGroup().PIDNamespace()
var targetTG *kernel.ThreadGroup
if tgid != 0 {
targetTG = currPidns.ThreadGroupWithID(kernel.ThreadID(tgid))
} else {
targetTG = t.ThreadGroup()
}
if targetTG == nil {
return 0, linuxerr.EINVAL
}
return n, targetTG.MigrateCgroup(d.CgroupFromControlFileFD(fd))
}
// +stateify savable
type tasksData struct {
*cgroupInode
}
// Generate implements vfs.DynamicBytesSource.Generate.
func (d *tasksData) Generate(ctx context.Context, buf *bytes.Buffer) error {
t := kernel.TaskFromContext(ctx)
currPidns := t.ThreadGroup().PIDNamespace()
var pids []kernel.ThreadID
for _, task := range d.tasks() {
if pid := currPidns.IDOfTask(task); pid != 0 {
pids = append(pids, pid)
}
}
sortTIDs(pids)
for _, pid := range pids {
fmt.Fprintf(buf, "%d\n", pid)
}
return nil
}
// Write implements vfs.WritableDynamicBytesSource.Write.
func (d *tasksData) Write(ctx context.Context, fd *vfs.FileDescription, src usermem.IOSequence, offset int64) (int64, error) {
tid, n, err := parseInt64FromString(ctx, src)
if err != nil {
return n, err
}
t := kernel.TaskFromContext(ctx)
currPidns := t.ThreadGroup().PIDNamespace()
var targetTask *kernel.Task
if tid != 0 {
targetTask = currPidns.TaskWithID(kernel.ThreadID(tid))
} else {
targetTask = t
}
if targetTask == nil {
return 0, linuxerr.EINVAL
}
return n, targetTask.MigrateCgroup(d.CgroupFromControlFileFD(fd))
}
// parseInt64FromString interprets src as string encoding a int64 value, and
// returns the parsed value.
func parseInt64FromString(ctx context.Context, src usermem.IOSequence) (val, len int64, err error) {
const maxInt64StrLen = 20 // i.e. len(fmt.Sprintf("%d", math.MinInt64)) == 20
buf := copyScratchBufferFromContext(ctx, maxInt64StrLen)
n, err := src.CopyIn(ctx, buf)
if err != nil {
return 0, int64(n), err
}
str := strings.TrimSpace(string(buf[:n]))
val, err = strconv.ParseInt(str, 10, 64)
if err != nil {
// Note: This also handles zero-len writes if offset is beyond the end
// of src, or src is empty.
ctx.Debugf("cgroupfs.parseInt64FromString: failed to parse %q: %v", str, err)
return 0, int64(n), linuxerr.EINVAL
}
return val, int64(n), nil
}
// copyScratchBufferFromContext returns a scratch buffer of the given size. It
// tries to use the task's copy scratch buffer if we're on a task context,
// otherwise it allocates a new buffer.
func copyScratchBufferFromContext(ctx context.Context, size int) []byte {
t := kernel.TaskFromContext(ctx)
if t != nil {
return t.CopyScratchBuffer(hostarch.PageSize)
}
// Not on task context.
return make([]byte, hostarch.PageSize)
}
// controllerStateless partially implements controller. It stubs the migration
// methods with noops for a stateless controller.
type controllerStateless struct{}
// Enter implements controller.Enter.
func (*controllerStateless) Enter(t *kernel.Task) {}
// Leave implements controller.Leave.
func (*controllerStateless) Leave(t *kernel.Task) {}
// PrepareMigrate implements controller.PrepareMigrate.
func (*controllerStateless) PrepareMigrate(t *kernel.Task, src controller) error {
return nil
}
// CommitMigrate implements controller.CommitMigrate.
func (*controllerStateless) CommitMigrate(t *kernel.Task, src controller) {}
// AbortMigrate implements controller.AbortMigrate.
func (*controllerStateless) AbortMigrate(t *kernel.Task, src controller) {}
// controllerNoResource partially implements controller. It stubs out the Charge
// method for controllers that don't track resource usage through the charge
// mechanism.
type controllerNoResource struct{}
// Charge implements controller.Charge.
func (*controllerNoResource) Charge(t *kernel.Task, d *kernfs.Dentry, res kernel.CgroupResourceType, value int64) error {
panic(fmt.Sprintf("cgroupfs: Attempted to charge a controller with unknown resource %v for value %v", res, value))
}