dotcloud/docker

//go:build linux || freebsd

package initlayer // import "github.com/docker/docker/daemon/initlayer"

import (
    "os"
    "path/filepath"
    "strings"

    "github.com/docker/docker/pkg/idtools"
    "golang.org/x/sys/unix"
)

// Setup populates a directory with mountpoints suitable
// for bind-mounting things into the container.
//
// This extra layer is used by all containers as the top-most ro layer. It protects
// the container from unwanted side-effects on the rw layer.
func Setup(initLayerFs string, rootIdentity idtools.Identity) error {
    // Since all paths are local to the container, we can just extract initLayerFs.Path()
    initLayer := initLayerFs

    for pth, typ := range map[string]string{
        "/dev/pts":         "dir",
        "/dev/shm":         "dir",
        "/proc":            "dir",
        "/sys":             "dir",
        "/.dockerenv":      "file",
        "/etc/resolv.conf": "file",
        "/etc/hosts":       "file",
        "/etc/hostname":    "file",
        "/dev/console":     "file",
        "/etc/mtab":        "/proc/mounts",
    } {
        parts := strings.Split(pth, "/")
        prev := "/"
        for _, p := range parts[1:] {
            prev = filepath.Join(prev, p)
            unix.Unlink(filepath.Join(initLayer, prev))
        }

        if _, err := os.Stat(filepath.Join(initLayer, pth)); err != nil {
            if os.IsNotExist(err) {
                if err := idtools.MkdirAllAndChownNew(filepath.Join(initLayer, filepath.Dir(pth)), 0o755, rootIdentity); err != nil {
                    return err
                }
                switch typ {
                case "dir":
                    if err := idtools.MkdirAllAndChownNew(filepath.Join(initLayer, pth), 0o755, rootIdentity); err != nil {
                        return err
                    }
                case "file":
                    f, err := os.OpenFile(filepath.Join(initLayer, pth), os.O_CREATE, 0o755)
                    if err != nil {
                        return err
                    }
                    f.Chown(rootIdentity.UID, rootIdentity.GID)
                    f.Close()
                default:
                    if err := os.Symlink(typ, filepath.Join(initLayer, pth)); err != nil {
                        return err
                    }
                }
            } else {
                return err
            }
        }
    }

    // Layer is ready to use, if it wasn't before.
    return nil
}