incusd/instance/lxc: Basic OCI support

Signed-off-by: Stéphane Graber <stgraber@stgraber.org>

cmd/incusd/main_forkstart.go

@@ -91,5 +91,11 @@ func (c *cmdForkstart) Run(cmd *cobra.Command, args []string) error {
 		_ = unix.Dup3(int(logFile.Fd()), 2, 0)
 	}
 
+	// Handle application containers.
+	execCmd := d.ConfigItem("lxc.execute.cmd")
+	if len(execCmd) > 0 && execCmd[0] != "" {
+		return d.StartExecute(nil)
+	}
+
 	return d.Start()
 }

internal/server/instance/drivers/driver_lxc.go

@@ -29,6 +29,7 @@ import (
 	"github.com/flosch/pongo2"
 	"github.com/google/uuid"
 	"github.com/gorilla/websocket"
+	"github.com/kballard/go-shellquote"
 	liblxc "github.com/lxc/go-lxc"
 	"github.com/pkg/sftp"
 	"golang.org/x/sync/errgroup"
@@ -2312,6 +2313,125 @@ func (d *lxc) startCommon() (string, []func() error, error) {
 		}
 	}
 
+	// Handle application containers.
+	if util.PathExists(filepath.Join(d.Path(), "config.json")) {
+		// Parse the OCI config.
+		data, err := os.ReadFile(filepath.Join(d.Path(), "config.json"))
+		if err != nil {
+			return "", nil, err
+		}
+
+		type ociConfig struct {
+			Process struct {
+				Terminal bool `json:"terminal"`
+				User     struct {
+					UID uint32 `json:"uid"`
+					GID uint32 `json:"gid"`
+				} `json:"user"`
+				Args []string `json:"args"`
+				Env  []string `json:"env"`
+				Cwd  string   `json:"cwd"`
+			} `json:"process"`
+		}
+
+		var config ociConfig
+		err = json.Unmarshal([]byte(data), &config)
+		if err != nil {
+			return "", nil, err
+		}
+
+		// FIXME: Should be moved to native environment.XYZ key.
+		for _, env := range config.Process.Env {
+			err = lxcSetConfigItem(cc, "lxc.environment", env)
+			if err != nil {
+				return "", nil, err
+			}
+		}
+
+		// Configure the entry point.
+		err = lxcSetConfigItem(cc, "lxc.execute.cmd", shellquote.Join(config.Process.Args...))
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.init.cwd", config.Process.Cwd)
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.init.uid", fmt.Sprintf("%d", config.Process.User.UID))
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.init.gid", fmt.Sprintf("%d", config.Process.User.GID))
+		if err != nil {
+			return "", nil, err
+		}
+
+		// Configure network handling.
+		err = os.MkdirAll(filepath.Join(d.Path(), "network"), 0711)
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = os.MkdirAll(filepath.Join(d.RootfsPath(), "etc"), 0755)
+		if err != nil && !os.IsExist(err) {
+			return "", nil, err
+		}
+
+		err = os.WriteFile(filepath.Join(d.Path(), "network", "hosts"), []byte(fmt.Sprintf(`127.0.0.1   localhost
+127.0.1.1   %s
+
+::1     localhost ip6-localhost ip6-loopback
+fe00::0 ip6-localnet
+ff00::0 ip6-mcastprefix
+ff02::1 ip6-allnodes
+ff02::2 ip6-allrouters
+`, d.name)), 0644)
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.mount.entry", fmt.Sprintf("%s etc/hosts none bind,create=file", filepath.Join(d.Path(), "network", "hosts")))
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = os.WriteFile(filepath.Join(d.Path(), "network", "hostname"), []byte(fmt.Sprintf("%s\n", d.name)), 0644)
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.mount.entry", fmt.Sprintf("%s etc/hostname none bind,create=file", filepath.Join(d.Path(), "network", "hostname")))
+		if err != nil {
+			return "", nil, err
+		}
+
+		f, err := os.Create(filepath.Join(d.Path(), "network", "resolv.conf"))
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = f.Chmod(0644)
+		if err != nil {
+			f.Close()
+			return "", nil, err
+		}
+
+		f.Close()
+
+		err = lxcSetConfigItem(cc, "lxc.mount.entry", fmt.Sprintf("%s etc/resolv.conf none bind,create=file", filepath.Join(d.Path(), "network", "resolv.conf")))
+		if err != nil {
+			return "", nil, err
+		}
+
+		err = lxcSetConfigItem(cc, "lxc.hook.start-host", fmt.Sprintf("/proc/%d/exe forknet dhcp %s", os.Getpid(), filepath.Join(d.Path(), "network")))
+		if err != nil {
+			return "", nil, err
+		}
+	}
+
 	// Load the LXC raw config.
 	err = d.loadRawLXCConfig(cc)
 	if err != nil {