Move tar copy-up for tmpfs mounts

We cannot rely on the tar command for this type of operation because tar
versions, flags, and functionality can very from distro to distro.
Since this is in the container execution path it is not safe to have
this as a dependency from dockers POV where the user cannot change the
fact that docker is adding these pre and post mount commands.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

daemon/execdriver/native/create.go

@@ -436,7 +436,6 @@ func (d *Driver) setupMounts(container *configs.Config, c *execdriver.Command) e
 				flags = syscall.MS_NOEXEC | syscall.MS_NOSUID | syscall.MS_NODEV
 				err   error
 			)
-			fulldest := filepath.Join(c.Rootfs, m.Destination)
 			if m.Data != "" {
 				flags, data, err = mount.ParseTmpfsOptions(m.Data)
 				if err != nil {
@@ -449,8 +448,6 @@ func (d *Driver) setupMounts(container *configs.Config, c *execdriver.Command) e
 				Data:             data,
 				Device:           "tmpfs",
 				Flags:            flags,
-				PremountCmds:     genTmpfsPremountCmd(c.TmpDir, fulldest, m.Destination),
-				PostmountCmds:    genTmpfsPostmountCmd(c.TmpDir, fulldest, m.Destination),
 				PropagationFlags: []int{mountPropagationMap[volume.DefaultPropagationMode]},
 			})
 			continue

daemon/execdriver/native/tmpfs.go

@@ -1,56 +0,0 @@
-package native
-
-import (
-	"fmt"
-	"os"
-	"os/exec"
-	"strings"
-
-	"github.com/Sirupsen/logrus"
-	"github.com/opencontainers/runc/libcontainer/configs"
-)
-
-func genTmpfsPremountCmd(tmpDir string, fullDest string, dest string) []configs.Command {
-	var premount []configs.Command
-	tarPath, err := exec.LookPath("tar")
-	if err != nil {
-		logrus.Warn("tar command is not available for tmpfs mount: %s", err)
-		return premount
-	}
-	if _, err = exec.LookPath("rm"); err != nil {
-		logrus.Warn("rm command is not available for tmpfs mount: %s", err)
-		return premount
-	}
-	tarFile := fmt.Sprintf("%s/%s.tar", tmpDir, strings.Replace(dest, "/", "_", -1))
-	if _, err := os.Stat(fullDest); err == nil {
-		premount = append(premount, configs.Command{
-			Path: tarPath,
-			Args: []string{"-cf", tarFile, "-C", fullDest, "."},
-		})
-	}
-	return premount
-}
-
-func genTmpfsPostmountCmd(tmpDir string, fullDest string, dest string) []configs.Command {
-	var postmount []configs.Command
-	tarPath, err := exec.LookPath("tar")
-	if err != nil {
-		return postmount
-	}
-	rmPath, err := exec.LookPath("rm")
-	if err != nil {
-		return postmount
-	}
-	if _, err := os.Stat(fullDest); os.IsNotExist(err) {
-		return postmount
-	}
-	tarFile := fmt.Sprintf("%s/%s.tar", tmpDir, strings.Replace(dest, "/", "_", -1))
-	postmount = append(postmount, configs.Command{
-		Path: tarPath,
-		Args: []string{"-xf", tarFile, "-C", fullDest, "."},
-	})
-	return append(postmount, configs.Command{
-		Path: rmPath,
-		Args: []string{"-f", tarFile},
-	})
-}

man/docker-create.1.md

@@ -319,10 +319,7 @@ unit, `b` is used. Set LIMIT to `-1` to enable unlimited swap.
 
    $ docker run -d --tmpfs /tmp:rw,size=787448k,mode=1777 my_image
 
-   This command mounts a `tmpfs` at `/tmp` within the container. The mount copies
-the underlying content of `my_image` into `/tmp`. For example if there was a
-directory `/tmp/content` in the base image, docker will copy this directory and
-all of its content on top of the tmpfs mounted on `/tmp`.  The supported mount
+   This command mounts a `tmpfs` at `/tmp` within the container.  The supported mount
 options are the same as the Linux default `mount` flags. If you do not specify
 any options, the systems uses the following options:
 `rw,noexec,nosuid,nodev,size=65536k`.

man/docker-run.1.md

@@ -490,10 +490,7 @@ standard input.
 
    $ docker run -d --tmpfs /tmp:rw,size=787448k,mode=1777 my_image
 
-   This command mounts a `tmpfs` at `/tmp` within the container. The mount copies
-the underlying content of `my_image` into `/tmp`. For example if there was a
-directory `/tmp/content` in the base image, docker will copy this directory and
-all of its content on top of the tmpfs mounted on `/tmp`.  The supported mount
+   This command mounts a `tmpfs` at `/tmp` within the container.  The supported mount
 options are the same as the Linux default `mount` flags. If you do not specify
 any options, the systems uses the following options:
 `rw,noexec,nosuid,nodev,size=65536k`.