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De-dup container root filesystems

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With the mount framework we can de-dup containers that share the same image.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>
This commit is contained in:
Justin Cormack
2017-08-22 17:27:08 +01:00
parent 6b98aff58b
commit cfa5d273b7
2 changed files with 39 additions and 13 deletions
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39
src/moby/image.go
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@@ -191,16 +191,28 @@ func ImageTar(image, prefix string, tw tarWriter, trust bool, pull bool, resolv
}
// ImageBundle produces an OCI bundle at the given path in a tarball, given an image and a config.json
func ImageBundle(prefix string, image string, config []byte, runtime Runtime, tw tarWriter, trust bool, pull bool, readonly bool) error {
func ImageBundle(prefix string, image string, config []byte, runtime Runtime, tw tarWriter, trust bool, pull bool, readonly bool, dupMap map[string]string) error {
// if read only, just unpack in rootfs/ but otherwise set up for overlay
rootfs := "rootfs"
rootExtract := "rootfs"
if !readonly {
rootfs = "lower"
rootExtract = "lower"
}
if err := ImageTar(image, path.Join(prefix, rootfs)+"/", tw, trust, pull, ""); err != nil {
return err
// See if we have extracted this image previously
root := path.Join(prefix, rootExtract)
var foundElsewhere = dupMap[image] != ""
if !foundElsewhere {
if err := ImageTar(image, root+"/", tw, trust, pull, ""); err != nil {
return err
}
dupMap[image] = root
} else {
if err := tarPrefix(prefix+"/", tw); err != nil {
return err
}
root = dupMap[image]
}
hdr := &tar.Header{
Name: path.Join(prefix, "config.json"),
Mode: 0644,
@@ -237,11 +249,22 @@ func ImageBundle(prefix string, image string, config []byte, runtime Runtime, tw
runtime.Mounts = append(runtime.Mounts, specs.Mount{Source: "tmpfs", Type: "tmpfs", Destination: "/" + tmp})
// remount private as nothing else should see the temporary layers
runtime.Mounts = append(runtime.Mounts, specs.Mount{Destination: "/" + tmp, Options: []string{"remount", "private"}})
overlayOptions := []string{"lowerdir=/" + path.Join(prefix, "lower"), "upperdir=/" + path.Join(tmp, "upper"), "workdir=/" + path.Join(tmp, "work")}
overlayOptions := []string{"lowerdir=/" + root, "upperdir=/" + path.Join(tmp, "upper"), "workdir=/" + path.Join(tmp, "work")}
runtime.Mounts = append(runtime.Mounts, specs.Mount{Source: "overlay", Type: "overlay", Destination: "/" + path.Join(prefix, "rootfs"), Options: overlayOptions})
} else {
// make rootfs a mountpoint as runc can be picky about this
runtime.Mounts = append(runtime.Mounts, specs.Mount{Source: path.Join(prefix, rootfs), Destination: "/" + path.Join(prefix, "rootfs"), Options: []string{"bind"}})
if foundElsewhere {
// we need to make the mountpoint at rootfs
hdr = &tar.Header{
Name: path.Join(prefix, "rootfs"),
Mode: 0755,
Typeflag: tar.TypeDir,
}
if err := tw.WriteHeader(hdr); err != nil {
return err
}
}
// either bind from another location, or bind from self to make sure it is a mountpoint as runc prefers this
runtime.Mounts = append(runtime.Mounts, specs.Mount{Source: "/" + root, Destination: "/" + path.Join(prefix, "rootfs"), Options: []string{"bind"}})
}
// write the runtime config