Add a sysfs container

However, do not try to change memory cgroups from it; this needs to be in `init`.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

examples/docker.yml

@@ -15,6 +15,8 @@ onboot:
     capabilities:
      - CAP_SYS_ADMIN
     readonly: true
+  - name: sysfs
+    image: mobylinux/sysfs:6c1d06f28ddd9681799d3950cddf044b930b221c
   - name: binfmt
     image: "mobylinux/binfmt:bdb754f25a5d851b4f5f8d185a43dfcbb3c22d01"
     binds:

pkg/sysfs/.gitignore

@@ -0,0 +1,4 @@
+dev
+proc
+sys
+usr

pkg/sysfs/Dockerfile

@@ -0,0 +1,3 @@
+FROM scratch
+COPY . ./
+CMD ["/usr/bin/sysfs"]

pkg/sysfs/Makefile

@@ -0,0 +1,44 @@
+GO_COMPILE=mobylinux/go-compile:3afebc59c5cde31024493c3f91e6102d584a30b9@sha256:e0786141ea7df8ba5735b63f2a24b4ade9eae5a02b0e04c4fca33b425ec69b0a
+
+SHA_IMAGE=alpine:3.5@sha256:dfbd4a3a8ebca874ebd2474f044a0b33600d4523d03b0df76e5c5986cb02d7e8
+
+SYSFS_BINARY=usr/bin/sysfs
+
+IMAGE=sysfs
+
+.PHONY: tag push clean container
+default: push
+
+$(SYSFS_BINARY): main.go
+	mkdir -p $(dir $@)
+	tar cf - $^ | docker run --rm --net=none --log-driver=none -i $(GO_COMPILE) -o $@ | tar xf -
+
+DIRS=dev proc sys
+$(DIRS):
+	mkdir -p $@
+
+DEPS=$(DIRS) $(SYSFS_BINARY) etc/sysfs.d/00-moby.conf
+
+container: Dockerfile $(DEPS)
+	tar cf - $^ | docker build --no-cache -t $(IMAGE):build -
+
+hash: Dockerfile $(DEPS)
+	find $^ -type f | xargs cat | docker run --rm -i $(SHA_IMAGE) sha1sum - | sed 's/ .*//' > hash
+
+push: hash container
+	docker pull mobylinux/$(IMAGE):$(shell cat hash) || \
+		(docker tag $(IMAGE):build mobylinux/$(IMAGE):$(shell cat hash) && \
+		 docker push mobylinux/$(IMAGE):$(shell cat hash))
+	docker rmi $(IMAGE):build
+	rm -f hash
+
+tag: hash container
+	docker pull mobylinux/$(IMAGE):$(shell cat hash) || \
+		docker tag $(IMAGE):build mobylinux/$(IMAGE):$(shell cat hash)
+	docker rmi $(IMAGE):build
+	rm -f hash
+
+clean:
+	rm -rf hash $(DIRS) usr
+
+.DELETE_ON_ERROR:

pkg/sysfs/etc/sysfs.d/00-moby.conf

@@ -0,0 +1,2 @@
+kernel/mm/transparent_hugepage/enabled = madvise
+kernel/mm/transparent_hugepage/defrag = madvise

pkg/sysfs/main.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var (
+	configDir string
+	sysfsDir  string
+)
+
+func init() {
+	flag.StringVar(&configDir, "configDir", "/etc/sysfs.d", "directory with config files")
+	flag.StringVar(&sysfsDir, "sysfsDir", "/sys", "mount point for sysfs")
+}
+
+func sysfs(line []byte) error {
+	// parse line into a string of expected form X/Y/Z=VALUE
+	sysfsLineKV := strings.Split(string(line[:]), "=")
+	if len(sysfsLineKV) != 2 {
+		if len(sysfsLineKV) >= 1 && len(sysfsLineKV[0]) >= 1 && strings.Trim(sysfsLineKV[0], " ")[:1] == "#" {
+			return nil
+		}
+		return fmt.Errorf("Cannot parse %s", string(line))
+	}
+	// trim any extra whitespace
+	sysfsSetting, sysfsValue := strings.Trim(sysfsLineKV[0], " "), strings.Trim(sysfsLineKV[1], " ")
+	sysfsFile := filepath.Join(sysfsDir, sysfsSetting)
+	file, err := os.OpenFile(sysfsFile, os.O_WRONLY, 0)
+	if err != nil {
+		return fmt.Errorf("Cannot open %s: %s", sysfsFile, err)
+	}
+	defer file.Close()
+	_, err = file.Write([]byte(sysfsValue))
+	if err != nil {
+		return fmt.Errorf("Cannot write to %s: %s", sysfsFile, err)
+	}
+	return nil
+}
+
+func main() {
+	flag.Parse()
+
+	files, err := ioutil.ReadDir(configDir)
+	if err != nil {
+		log.Fatalf("Cannot read directory %s: %s", configDir, err)
+	}
+
+	for _, file := range files {
+		contents, err := ioutil.ReadFile(filepath.Join(configDir, file.Name()))
+		if err != nil {
+			log.Fatalf("Cannot read file %s: %s", file.Name(), err)
+		}
+		lines := bytes.Split(contents, []byte("\n"))
+		for _, line := range lines {
+			if len(line) == 0 {
+				continue
+			}
+			err = sysfs(line)
+			if err != nil {
+				log.Fatal(err)
+			}
+		}
+	}
+}