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machine.go
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machine.go
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package vm
import (
"context"
"encoding/json"
"fmt"
"os"
"os/exec"
"path/filepath"
"strings"
"syscall"
"github.com/pkg/errors"
)
// Boot config struct
type Boot struct {
Kernel string `json:"kernel_image_path"`
Initrd string `json:"initrd_path,omitempty"`
Args string `json:"boot_args"`
}
// Drive struct
type Drive struct {
ID string `json:"drive_id"`
Path string `json:"path_on_host"`
RootDevice bool `json:"is_root_device"`
ReadOnly bool `json:"is_read_only"`
}
// Interface nic struct
type Interface struct {
ID string `json:"iface_id"`
Tap string `json:"host_dev_name"`
Mac string `json:"guest_mac,omitempty"`
}
// Config struct
type Config struct {
CPU uint8 `json:"vcpu_count"`
Mem int64 `json:"mem_size_mib"`
HTEnabled bool `json:"ht_enabled"`
}
// Machine struct
type Machine struct {
ID string `json:"-"`
Boot Boot `json:"boot-source"`
Drives []Drive `json:"drives"`
Interfaces []Interface `json:"network-interfaces"`
Config Config `json:"machine-config"`
}
func (m *Machine) root(base string) string {
return filepath.Join(base, "firecracker", m.ID, "root")
}
func mount(src, dest string) error {
if filepath.Clean(src) == filepath.Clean(dest) {
// nothing to do here
return nil
}
f, err := os.Create(dest)
if err != nil {
return errors.Wrapf(err, "failed to touch file: %s", dest)
}
f.Close()
if err := syscall.Mount(src, dest, "", syscall.MS_BIND, ""); err != nil {
return errors.Wrapf(err, "failed to mount '%s' > '%s'", src, dest)
}
return nil
}
// Jail will move files to machine root and update a "jailed"
// copy of the config to reference correct files.
func (m *Machine) jail(root string) (Machine, error) {
cfg := *m
if err := os.MkdirAll(root, 0755); err != nil {
return cfg, err
}
rooted := func(f string) string {
return filepath.Join(root, filepath.Base(f))
}
for _, str := range []*string{&cfg.Boot.Kernel, &cfg.Boot.Initrd} {
file := *str
if len(file) == 0 {
continue
}
// mount kernel
if err := mount(file, rooted(file)); err != nil {
return cfg, err
}
*str = filepath.Base(file)
}
// mount drives
for i, drive := range cfg.Drives {
name := filepath.Base(drive.Path)
if err := mount(drive.Path, rooted(drive.Path)); err != nil {
return cfg, err
}
m.Drives[i].Path = name
}
return cfg, nil
}
// Start starts the machine.
func (m *Machine) Start(ctx context.Context, base string) error {
root := m.root(base)
if err := os.MkdirAll(root, 0755); err != nil {
return errors.Wrap(err, "failed to create machine root")
}
jailed, err := m.jail(root)
if err != nil {
return errors.Wrap(err, "failed to jail files")
}
cfg, err := os.Create(filepath.Join(root, "config.json"))
if err != nil {
return errors.Wrap(err, "failed to write config file")
}
defer cfg.Close()
enc := json.NewEncoder(cfg)
if err := enc.Encode(jailed); err != nil {
return err
}
cfg.Close()
return jailed.exec(ctx, base)
}
// Log returns machine log file path
func (m *Machine) Log(base string) string {
return filepath.Join(m.root(base), "machine.log")
}
func (m *Machine) exec(ctx context.Context, base string) error {
// prepare command
// because the --daemonize flag does not work as expected
// we are daemonizing with `ash and &` so we can use cmd.Run().
// the reason we don't want to use 'cmd.Start' instead of 'cmd.Run'
// is that if we do 'Start' and then the process exited for some reason
// we will endup with 'zombi' process because vmd did not 'wait' for the
// process exit. hence daemonizing is required.
// due to issues with jailer --daemonize flag, we use the ash trick below
jailerBin, err := exec.LookPath("jailer")
if err != nil {
return err
}
fcBin, err := exec.LookPath("firecracker")
if err != nil {
return err
}
args := []string{
jailerBin,
"--id", m.ID,
"--uid", "0", "--gid", "0",
"--chroot-base-dir", base, // this stupid flag creates so many layers but is needed
"--exec-file", fcBin,
"--node", "0",
"--", // fc flags starts here
"--config-file", "/config.json",
"--api-sock", "/api.socket",
}
const (
// if this is enabled machine will start in the
// foreground. It's then required that vmd
// was also started from the cmdline not as a
// daemon so you have access to machine console
testing = false
)
logFile := m.Log(base)
var cmd *exec.Cmd
if !testing {
cmd = exec.CommandContext(ctx,
"ash", "-c",
fmt.Sprintf("%s > %s 2>&1 &", strings.Join(args, " "), logFile),
)
} else {
cmd = exec.CommandContext(ctx,
args[0], args[1:]...,
)
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
}
return cmd.Run()
}