// Copyright 2015 Google Inc. All Rights Reserved.
//
// 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 netlink
import (
"bytes"
"encoding/binary"
"fmt"
"os"
"syscall"
"golang.org/x/sys/unix"
info "github.com/google/cadvisor/info/v1"
)
var (
// TODO(rjnagal): Verify and fix for other architectures.
Endian = binary.LittleEndian
)
type genMsghdr struct {
Command uint8
Version uint8
Reserved uint16
}
type netlinkMessage struct {
Header syscall.NlMsghdr
GenHeader genMsghdr
Data []byte
}
func (m netlinkMessage) toRawMsg() (rawmsg syscall.NetlinkMessage) {
rawmsg.Header = m.Header
w := bytes.NewBuffer([]byte{})
binary.Write(w, Endian, m.GenHeader)
w.Write(m.Data)
rawmsg.Data = w.Bytes()
return rawmsg
}
type loadStatsResp struct {
Header syscall.NlMsghdr
GenHeader genMsghdr
Stats info.LoadStats
}
// Return required padding to align 'size' to 'alignment'.
func padding(size int, alignment int) int {
unalignedPart := size % alignment
return (alignment - unalignedPart) % alignment
}
// Get family id for taskstats subsystem.
func getFamilyID(conn *Connection) (uint16, error) {
msg := prepareFamilyMessage()
err := conn.WriteMessage(msg.toRawMsg())
if err != nil {
return 0, err
}
resp, err := conn.ReadMessage()
if err != nil {
return 0, err
}
id, err := parseFamilyResp(resp)
if err != nil {
return 0, err
}
return id, nil
}
// Append an attribute to the message.
// Adds attribute info (length and type), followed by the data and necessary padding.
// Can be called multiple times to add attributes. Only fixed size and string type
// attributes are handled. We don't need nested attributes for task stats.
func addAttribute(buf *bytes.Buffer, attrType uint16, data interface{}, dataSize int) {
attr := syscall.RtAttr{
Len: syscall.SizeofRtAttr,
Type: attrType,
}
attr.Len += uint16(dataSize)
binary.Write(buf, Endian, attr)
switch data := data.(type) {
case string:
binary.Write(buf, Endian, []byte(data))
buf.WriteByte(0) // terminate
default:
binary.Write(buf, Endian, data)
}
for i := 0; i < padding(int(attr.Len), syscall.NLMSG_ALIGNTO); i++ {
buf.WriteByte(0)
}
}
// Prepares the message and generic headers and appends attributes as data.
func prepareMessage(headerType uint16, cmd uint8, attributes []byte) (msg netlinkMessage) {
msg.Header.Type = headerType
msg.Header.Flags = syscall.NLM_F_REQUEST
msg.GenHeader.Command = cmd
msg.GenHeader.Version = 0x1
msg.Data = attributes
return msg
}
// Prepares message to query family id for task stats.
func prepareFamilyMessage() (msg netlinkMessage) {
buf := bytes.NewBuffer([]byte{})
addAttribute(buf, unix.CTRL_ATTR_FAMILY_NAME, unix.TASKSTATS_GENL_NAME, len(unix.TASKSTATS_GENL_NAME)+1)
return prepareMessage(unix.GENL_ID_CTRL, unix.CTRL_CMD_GETFAMILY, buf.Bytes())
}
// Prepares message to query task stats for a task group.
func prepareCmdMessage(id uint16, cfd uintptr) (msg netlinkMessage) {
buf := bytes.NewBuffer([]byte{})
addAttribute(buf, unix.CGROUPSTATS_CMD_ATTR_FD, uint32(cfd), 4)
return prepareMessage(id, unix.CGROUPSTATS_CMD_GET, buf.Bytes())
}
// Extracts returned family id from the response.
func parseFamilyResp(msg syscall.NetlinkMessage) (uint16, error) {
m := new(netlinkMessage)
m.Header = msg.Header
err := verifyHeader(msg)
if err != nil {
return 0, err
}
buf := bytes.NewBuffer(msg.Data)
// extract generic header from data.
err = binary.Read(buf, Endian, &m.GenHeader)
if err != nil {
return 0, err
}
id := uint16(0)
// Extract attributes. kernel reports family name, id, version, etc.
// Scan till we find id.
for buf.Len() > syscall.SizeofRtAttr {
var attr syscall.RtAttr
err = binary.Read(buf, Endian, &attr)
if err != nil {
return 0, err
}
if attr.Type == unix.CTRL_ATTR_FAMILY_ID {
err = binary.Read(buf, Endian, &id)
if err != nil {
return 0, err
}
return id, nil
}
payload := int(attr.Len) - syscall.SizeofRtAttr
skipLen := payload + padding(payload, syscall.SizeofRtAttr)
name := make([]byte, skipLen)
err = binary.Read(buf, Endian, name)
if err != nil {
return 0, err
}
}
return 0, fmt.Errorf("family id not found in the response")
}
// Extract task stats from response returned by kernel.
func parseLoadStatsResp(msg syscall.NetlinkMessage) (*loadStatsResp, error) {
m := new(loadStatsResp)
m.Header = msg.Header
err := verifyHeader(msg)
if err != nil {
return m, err
}
buf := bytes.NewBuffer(msg.Data)
// Scan the general header.
err = binary.Read(buf, Endian, &m.GenHeader)
if err != nil {
return m, err
}
// cgroup stats response should have just one attribute.
// Read it directly into the stats structure.
var attr syscall.RtAttr
err = binary.Read(buf, Endian, &attr)
if err != nil {
return m, err
}
err = binary.Read(buf, Endian, &m.Stats)
if err != nil {
return m, err
}
return m, err
}
// Verify and return any error reported by kernel.
func verifyHeader(msg syscall.NetlinkMessage) error {
switch msg.Header.Type {
case syscall.NLMSG_DONE:
return fmt.Errorf("expected a response, got nil")
case syscall.NLMSG_ERROR:
buf := bytes.NewBuffer(msg.Data)
var errno int32
err := binary.Read(buf, Endian, errno)
if err != nil {
return err
}
return fmt.Errorf("netlink request failed with error %s", syscall.Errno(-errno))
}
return nil
}
// Get load stats for a task group.
// id: family id for taskstats.
// cfd: open file to path to the cgroup directory under cpu hierarchy.
// conn: open netlink connection used to communicate with kernel.
func getLoadStats(id uint16, cfd *os.File, conn *Connection) (info.LoadStats, error) {
msg := prepareCmdMessage(id, cfd.Fd())
err := conn.WriteMessage(msg.toRawMsg())
if err != nil {
return info.LoadStats{}, err
}
resp, err := conn.ReadMessage()
if err != nil {
return info.LoadStats{}, err
}
parsedmsg, err := parseLoadStatsResp(resp)
if err != nil {
return info.LoadStats{}, err
}
return parsedmsg.Stats, nil
}
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