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Move all bind-mounts in the container inside the namespace 

This moves the bind mounts like /.dockerinit, /etc/hostname, volumes,
etc into the container namespace, by setting them up using lxc.

This is useful to avoid littering the global namespace with a lot of
mounts that are internal to each container and are not generally
needed on the outside. In particular, it seems that having a lot of
mounts is problematic wrt scaling to a lot of containers on systems
where the root filesystem is mounted --rshared.

Note that the "private" option is only supported by the native driver, as
lxc doesn't support setting this. This is not a huge problem, but it does
mean that some mounts are unnecessarily shared inside the container if you're
using the lxc driver.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
This commit is contained in:
Alexander Larsson 2014-03-03 16:15:29 +01:00
parent 4b8a574f8f
commit 9e71710125
3 changed files with 30 additions and 2 deletions
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10
container.go
View File

@ -23,6 +23,7 @@ type Container struct {
Networks []*Network `json:"networks,omitempty"` // nil for host's network stack
Cgroups *cgroups.Cgroup `json:"cgroups,omitempty"` // cgroups
Context Context `json:"context,omitempty"` // generic context for specific options (apparmor, selinux)
Mounts []Mount `json:"mounts,omitempty"`
}
// Network defines configuration for a container's networking stack
@ -36,3 +37,12 @@ type Network struct {
Gateway string `json:"gateway,omitempty"`
Mtu int `json:"mtu,omitempty"`
}
// Bind mounts from the host system to the container
//
type Mount struct {
Source string `json:"source"` // Source path, in the host namespace
Destination string `json:"destination"` // Destination path, in the container
Writable bool `json:"writable"`
Private bool `json:"private"`
}

2
nsinit/init.go
View File

@ -51,7 +51,7 @@ func (ns *linuxNs) Init(container *libcontainer.Container, uncleanRootfs, consol
if err := system.ParentDeathSignal(); err != nil {
return fmt.Errorf("parent death signal %s", err)
}
if err := setupNewMountNamespace(rootfs, console, container.ReadonlyFs, container.NoPivotRoot); err != nil {
if err := setupNewMountNamespace(rootfs, container.Mounts, console, container.ReadonlyFs, container.NoPivotRoot); err != nil {
return fmt.Errorf("setup mount namespace %s", err)
}
if err := setupNetwork(container, context); err != nil {

20
nsinit/mount.go
View File

@ -4,6 +4,7 @@ package nsinit
import (
"fmt"
"github.com/dotcloud/docker/pkg/libcontainer"
"github.com/dotcloud/docker/pkg/system"
"io/ioutil"
"os"
@ -19,7 +20,7 @@ const defaultMountFlags = syscall.MS_NOEXEC | syscall.MS_NOSUID | syscall.MS_NOD
//
// There is no need to unmount the new mounts because as soon as the mount namespace
// is no longer in use, the mounts will be removed automatically
func setupNewMountNamespace(rootfs, console string, readonly, noPivotRoot bool) error {
func setupNewMountNamespace(rootfs string, bindMounts []libcontainer.Mount, console string, readonly, noPivotRoot bool) error {
flag := syscall.MS_PRIVATE
if noPivotRoot {
flag = syscall.MS_SLAVE
@ -38,6 +39,23 @@ func setupNewMountNamespace(rootfs, console string, readonly, noPivotRoot bool)
if err := mountSystem(rootfs); err != nil {
return fmt.Errorf("mount system %s", err)
}
for _, m := range bindMounts {
flags := syscall.MS_BIND | syscall.MS_REC
if !m.Writable {
flags = flags | syscall.MS_RDONLY
}
dest := filepath.Join(rootfs, m.Destination)
if err := system.Mount(m.Source, dest, "bind", uintptr(flags), ""); err != nil {
return fmt.Errorf("mounting %s into %s %s", m.Source, dest, err)
}
if m.Private {
if err := system.Mount("", dest, "none", uintptr(syscall.MS_PRIVATE), ""); err != nil {
return fmt.Errorf("mounting %s private %s", dest, err)
}
}
}
if err := copyDevNodes(rootfs); err != nil {
return fmt.Errorf("copy dev nodes %s", err)
}