Merge pull request #34550 from kolyshkin/libeudev

Update Dockerfiles to use Debian Stretch

Dockerfile

@@ -23,7 +23,7 @@
 # the case. Therefore, you don't have to disable it anymore.
 #
 
-FROM debian:jessie
+FROM debian:stretch
 
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org
@@ -51,21 +51,28 @@ RUN apt-get update && apt-get install -y \
 	less \
 	libapparmor-dev \
 	libcap-dev \
+	libdevmapper-dev \
 	libnl-3-dev \
 	libprotobuf-c0-dev \
 	libprotobuf-dev \
-	libsystemd-journal-dev \
+	libsystemd-dev \
 	libtool \
+	libudev-dev \
 	mercurial \
 	net-tools \
 	pkg-config \
 	protobuf-compiler \
 	protobuf-c-compiler \
+	python-backports.ssl-match-hostname \
 	python-dev \
 	python-mock \
 	python-pip \
+	python-requests \
+	python-setuptools \
 	python-websocket \
+	python-wheel \
 	tar \
+	thin-provisioning-tools \
 	vim \
 	vim-common \
 	xfsprogs \
@@ -73,21 +80,6 @@ RUN apt-get update && apt-get install -y \
 	--no-install-recommends \
 	&& pip install awscli==1.10.15
 
-# Get lvm2 sources to build statically linked devmapper library
-ENV LVM2_VERSION 2.02.168
-RUN mkdir -p /usr/local/lvm2 \
-	&& curl -fsSL "https://mirrors.kernel.org/sourceware/lvm2/LVM2.${LVM2_VERSION}.tgz" \
-		| tar -xzC /usr/local/lvm2 --strip-components=1
-
-# Compile and install (only the needed library)
-RUN cd /usr/local/lvm2 \
-	&& ./configure \
-		--build="$(gcc -print-multiarch)" \
-		--enable-static_link \
-		--enable-pkgconfig \
-	&& make -C include \
-	&& make -C libdm install_device-mapper
-
 # Install seccomp: the version shipped upstream is too old
 ENV SECCOMP_VERSION 2.3.2
 RUN set -x \
@@ -157,9 +149,6 @@ RUN set -x \
 # Get the "docker-py" source so we can run their integration tests
 ENV DOCKER_PY_COMMIT a962578e515185cf06506050b2200c0b81aa84ef
 # To run integration tests docker-pycreds is required.
-# Before running the integration tests conftest.py is
-# loaded which results in loads auth.py that
-# imports the docker-pycreds module.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \

Dockerfile.aarch64

@@ -15,14 +15,20 @@
 # the case. Therefore, you don't have to disable it anymore.
 #
 
-FROM aarch64/ubuntu:xenial
+FROM arm64v8/debian:stretch
+
+# allow replacing httpredir or deb mirror
+ARG APT_MIRROR=deb.debian.org
+RUN sed -ri "s/(httpredir|deb).debian.org/$APT_MIRROR/g" /etc/apt/sources.list
 
 # Packaged dependencies
 RUN apt-get update && apt-get install -y \
 	apparmor \
+	apt-utils \
 	aufs-tools \
 	automake \
 	bash-completion \
+	bsdmainutils \
 	btrfs-tools \
 	build-essential \
 	cmake \
@@ -32,43 +38,40 @@ RUN apt-get update && apt-get install -y \
 	g++ \
 	gcc \
 	git \
+	golang \
 	iptables \
 	jq \
+	less \
 	libapparmor-dev \
-	libc6-dev \
 	libcap-dev \
+	libdevmapper-dev \
+	libnl-3-dev \
+	libprotobuf-c0-dev \
+	libprotobuf-dev \
 	libsystemd-dev \
-	libyaml-dev \
+	libtool \
+	libudev-dev \
 	mercurial \
 	net-tools \
-	parallel \
 	pkg-config \
+	protobuf-compiler \
+	protobuf-c-compiler \
+	python-backports.ssl-match-hostname \
 	python-dev \
 	python-mock \
 	python-pip \
+	python-requests \
 	python-setuptools \
 	python-websocket \
-	golang-go \
-	iproute2 \
-	iputils-ping \
+	python-wheel \
+	tar \
+	thin-provisioning-tools \
+	vim \
 	vim-common \
+	xfsprogs \
+	zip \
 	--no-install-recommends
 
-# Get lvm2 sources to build statically linked devmapper library
-ENV LVM2_VERSION 2.02.168
-RUN mkdir -p /usr/local/lvm2 \
-	&& curl -fsSL "https://mirrors.kernel.org/sourceware/lvm2/LVM2.${LVM2_VERSION}.tgz" \
-		| tar -xzC /usr/local/lvm2 --strip-components=1
-
-# Compile and install (only the needed library)
-RUN cd /usr/local/lvm2 \
-	&& ./configure \
-		--build="$(gcc -print-multiarch)" \
-		--enable-static_link \
-		--enable-pkgconfig \
-	&& make -C include \
-	&& make -C libdm install_device-mapper
-
 # Install seccomp: the version shipped upstream is too old
 ENV SECCOMP_VERSION 2.3.2
 RUN set -x \
@@ -86,9 +89,7 @@ RUN set -x \
 
 # Install Go
 # We don't have official binary golang 1.7.5 tarballs for ARM64, either for Go or
-# bootstrap, so we use golang-go (1.6) as bootstrap to build Go from source code.
-# We don't use the official ARMv6 released binaries as a GOROOT_BOOTSTRAP, because
-# not all ARM64 platforms support 32-bit mode. 32-bit mode is optional for ARMv8.
+# bootstrap, so we use Debian golang (1.7) as bootstrap to build Go from source code.
 # IMPORTANT: When updating this please note that stdlib archive/tar pkg is vendored
 ENV GO_VERSION 1.8.3
 RUN mkdir /usr/src/go && curl -fsSL https://golang.org/dl/go${GO_VERSION}.src.tar.gz | tar -v -C /usr/src/go -xz --strip-components=1 \
@@ -124,13 +125,10 @@ RUN set -x \
 
 # Get the "docker-py" source so we can run their integration tests
 ENV DOCKER_PY_COMMIT a962578e515185cf06506050b2200c0b81aa84ef
-# Before running the integration tests conftest.py is
-# loaded which results in loads auth.py that
-# imports the docker-pycreds module.
+# To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \
-	&& pip install wheel \
 	&& pip install docker-pycreds==0.2.1 \
 	&& pip install -r test-requirements.txt
 

Dockerfile.armhf

@@ -15,7 +15,7 @@
 # the case. Therefore, you don't have to disable it anymore.
 #
 
-FROM armhf/debian:jessie
+FROM arm32v7/debian:stretch
 
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org
@@ -39,36 +39,27 @@ RUN apt-get update && apt-get install -y \
 	net-tools \
 	libapparmor-dev \
 	libcap-dev \
-	libsystemd-journal-dev \
+	libdevmapper-dev \
+	libsystemd-dev \
 	libtool \
+	libudev-dev \
 	mercurial \
 	pkg-config \
+	python-backports.ssl-match-hostname \
 	python-dev \
 	python-mock \
 	python-pip \
+	python-requests \
+	python-setuptools \
 	python-websocket \
+	python-wheel \
 	xfsprogs \
 	tar \
+	thin-provisioning-tools \
 	vim-common \
 	--no-install-recommends \
 	&& pip install awscli==1.10.15
 
-# Get lvm2 sources to build statically linked devmapper library
-ENV LVM2_VERSION 2.02.168
-RUN mkdir -p /usr/local/lvm2 \
-	&& curl -fsSL "https://mirrors.kernel.org/sourceware/lvm2/LVM2.${LVM2_VERSION}.tgz" \
-		| tar -xzC /usr/local/lvm2 --strip-components=1
-
-# Compile and install (only the needed library)
-RUN cd /usr/local/lvm2 \
-	&& ./configure \
-		--build="$(gcc -print-multiarch)" \
-		--enable-static_link \
-		--enable-pkgconfig \
-	&& make -C include \
-	&& make -C libdm install_device-mapper
-
-
 # Install Go
 # IMPORTANT: When updating this please note that stdlib archive/tar pkg is vendored
 ENV GO_VERSION 1.8.3
@@ -127,9 +118,11 @@ RUN set -x \
 
 # Get the "docker-py" source so we can run their integration tests
 ENV DOCKER_PY_COMMIT a962578e515185cf06506050b2200c0b81aa84ef
+# To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \
+	&& pip install docker-pycreds==0.2.1 \
 	&& pip install -r test-requirements.txt
 
 # Set user.email so crosbymichael's in-container merge commits go smoothly

Dockerfile.ppc64le

@@ -15,7 +15,7 @@
 # the case. Therefore, you don't have to disable it anymore.
 #
 
-FROM ppc64le/debian:jessie
+FROM ppc64le/debian:stretch
 
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org
@@ -40,34 +40,26 @@ RUN apt-get update && apt-get install -y \
 	net-tools \
 	libapparmor-dev \
 	libcap-dev \
-	libsystemd-journal-dev \
+	libdevmapper-dev \
+	libsystemd-dev \
 	libtool \
+	libudev-dev \
 	mercurial \
 	pkg-config \
+	python-backports.ssl-match-hostname \
 	python-dev \
 	python-mock \
 	python-pip \
+	python-requests \
+	python-setuptools \
 	python-websocket \
+	python-wheel \
 	xfsprogs \
 	tar \
+	thin-provisioning-tools \
 	vim-common \
 	--no-install-recommends
 
-# Get lvm2 sources to build statically linked devmapper library
-ENV LVM2_VERSION 2.02.168
-RUN mkdir -p /usr/local/lvm2 \
-	&& curl -fsSL "https://mirrors.kernel.org/sourceware/lvm2/LVM2.${LVM2_VERSION}.tgz" \
-		| tar -xzC /usr/local/lvm2 --strip-components=1
-
-# Compile and install (only the needed library)
-RUN cd /usr/local/lvm2 \
-	&& ./configure \
-		--build="$(gcc -print-multiarch)" \
-		--enable-static_link \
-		--enable-pkgconfig \
-	&& make -C include \
-	&& make -C libdm install_device-mapper
-
 # Install seccomp: the version shipped upstream is too old
 ENV SECCOMP_VERSION 2.3.2
 RUN set -x \
@@ -125,9 +117,11 @@ RUN set -x \
 
 # Get the "docker-py" source so we can run their integration tests
 ENV DOCKER_PY_COMMIT a962578e515185cf06506050b2200c0b81aa84ef
+# To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \
+	&& pip install docker-pycreds==0.2.1 \
 	&& pip install -r test-requirements.txt
 
 # Set user.email so crosbymichael's in-container merge commits go smoothly

Dockerfile.s390x

@@ -15,7 +15,7 @@
 # the case. Therefore, you don't have to disable it anymore.
 #
 
-FROM s390x/debian:jessie
+FROM s390x/debian:stretch
 
 # Packaged dependencies
 RUN apt-get update && apt-get install -y \
@@ -36,16 +36,23 @@ RUN apt-get update && apt-get install -y \
 	net-tools \
 	libapparmor-dev \
 	libcap-dev \
-	libsystemd-journal-dev \
+	libdevmapper-dev \
+	libsystemd-dev \
 	libtool \
+	libudev-dev \
 	mercurial \
 	pkg-config \
+	python-backports.ssl-match-hostname \
 	python-dev \
 	python-mock \
 	python-pip \
+	python-requests \
+	python-setuptools \
 	python-websocket \
+	python-wheel \
 	xfsprogs \
 	tar \
+	thin-provisioning-tools \
 	vim-common \
 	--no-install-recommends
 
@@ -64,21 +71,6 @@ RUN set -x \
 	) \
 	&& rm -rf "$SECCOMP_PATH"
 
-# Get lvm2 sources to build statically linked devmapper library
-ENV LVM2_VERSION 2.02.168
-RUN mkdir -p /usr/local/lvm2 \
-	&& curl -fsSL "https://mirrors.kernel.org/sourceware/lvm2/LVM2.${LVM2_VERSION}.tgz" \
-		| tar -xzC /usr/local/lvm2 --strip-components=1
-
-# Compile and install (only the needed library)
-RUN cd /usr/local/lvm2 \
-	&& ./configure \
-		--build="$(gcc -print-multiarch)" \
-		--enable-static_link \
-		--enable-pkgconfig \
-	&& make -C include \
-	&& make -C libdm install_device-mapper
-
 # IMPORTANT: When updating this please note that stdlib archive/tar pkg is vendored
 ENV GO_VERSION 1.8.3
 RUN curl -fsSL "https://golang.org/dl/go${GO_VERSION}.linux-s390x.tar.gz" \
@@ -118,9 +110,11 @@ RUN set -x \
 
 # Get the "docker-py" source so we can run their integration tests
 ENV DOCKER_PY_COMMIT a962578e515185cf06506050b2200c0b81aa84ef
+# To run integration tests docker-pycreds is required.
 RUN git clone https://github.com/docker/docker-py.git /docker-py \
 	&& cd /docker-py \
 	&& git checkout -q $DOCKER_PY_COMMIT \
+	&& pip install docker-pycreds==0.2.1 \
 	&& pip install -r test-requirements.txt
 
 # Set user.email so crosbymichael's in-container merge commits go smoothly

Dockerfile.simple

@@ -5,7 +5,7 @@
 
 # This represents the bare minimum required to build and test Docker.
 
-FROM debian:jessie
+FROM debian:stretch
 
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org

daemon/graphdriver/devmapper/deviceset.go

@@ -21,10 +21,12 @@ import (
 	"github.com/docker/docker/daemon/graphdriver"
 	"github.com/docker/docker/dockerversion"
 	"github.com/docker/docker/pkg/devicemapper"
+	"github.com/docker/docker/pkg/dmesg"
 	"github.com/docker/docker/pkg/idtools"
 	"github.com/docker/docker/pkg/loopback"
 	"github.com/docker/docker/pkg/mount"
 	"github.com/docker/docker/pkg/parsers"
+	"github.com/docker/docker/pkg/parsers/kernel"
 	units "github.com/docker/go-units"
 	"github.com/opencontainers/selinux/go-selinux/label"
 	"github.com/pkg/errors"
@@ -533,11 +535,11 @@ func (devices *DeviceSet) activateDeviceIfNeeded(info *devInfo, ignoreDeleted bo
 	return devicemapper.ActivateDevice(devices.getPoolDevName(), info.Name(), info.DeviceID, info.Size)
 }
 
-// Return true only if kernel supports xfs and mkfs.xfs is available
-func xfsSupported() bool {
+// xfsSupported checks if xfs is supported, returns nil if it is, otherwise an error
+func xfsSupported() error {
 	// Make sure mkfs.xfs is available
 	if _, err := exec.LookPath("mkfs.xfs"); err != nil {
-		return false
+		return err // error text is descriptive enough
 	}
 
 	// Check if kernel supports xfs filesystem or not.
@@ -545,40 +547,47 @@ func xfsSupported() bool {
 
 	f, err := os.Open("/proc/filesystems")
 	if err != nil {
-		logrus.Warnf("devmapper: Could not check if xfs is supported: %v", err)
-		return false
+		return errors.Wrapf(err, "error checking for xfs support")
 	}
 	defer f.Close()
 
 	s := bufio.NewScanner(f)
 	for s.Scan() {
 		if strings.HasSuffix(s.Text(), "\txfs") {
-			return true
+			return nil
 		}
 	}
 
 	if err := s.Err(); err != nil {
-		logrus.Warnf("devmapper: Could not check if xfs is supported: %v", err)
+		return errors.Wrapf(err, "error checking for xfs support")
 	}
-	return false
+
+	return errors.New(`kernel does not support xfs, or "modprobe xfs" failed`)
 }
 
 func determineDefaultFS() string {
-	if xfsSupported() {
+	err := xfsSupported()
+	if err == nil {
 		return "xfs"
 	}
 
-	logrus.Warn("devmapper: XFS is not supported in your system. Either the kernel doesn't support it or mkfs.xfs is not in your PATH. Defaulting to ext4 filesystem")
+	logrus.Warnf("devmapper: XFS is not supported in your system (%v). Defaulting to ext4 filesystem", err)
 	return "ext4"
 }
 
-func (devices *DeviceSet) createFilesystem(info *devInfo) (err error) {
-	devname := info.DevName()
+// mkfsOptions tries to figure out whether some additional mkfs options are required
+func mkfsOptions(fs string) []string {
+	if fs == "xfs" && !kernel.CheckKernelVersion(3, 16, 0) {
+		// For kernels earlier than 3.16 (and newer xfsutils),
+		// some xfs features need to be explicitly disabled.
+		return []string{"-m", "crc=0,finobt=0"}
+	}
 
-	args := []string{}
-	args = append(args, devices.mkfsArgs...)
+	return []string{}
+}
 
-	args = append(args, devname)
+func (devices *DeviceSet) createFilesystem(info *devInfo) (err error) {
+	devname := info.DevName()
 
 	if devices.filesystem == "" {
 		devices.filesystem = determineDefaultFS()
@@ -587,7 +596,11 @@ func (devices *DeviceSet) createFilesystem(info *devInfo) (err error) {
 		return err
 	}
 
-	logrus.Infof("devmapper: Creating filesystem %s on device %s", devices.filesystem, info.Name())
+	args := mkfsOptions(devices.filesystem)
+	args = append(args, devices.mkfsArgs...)
+	args = append(args, devname)
+
+	logrus.Infof("devmapper: Creating filesystem %s on device %s, mkfs args: %v", devices.filesystem, info.Name(), args)
 	defer func() {
 		if err != nil {
 			logrus.Infof("devmapper: Error while creating filesystem %s on device %s: %v", devices.filesystem, info.Name(), err)
@@ -1188,7 +1201,7 @@ func (devices *DeviceSet) growFS(info *devInfo) error {
 	options = joinMountOptions(options, devices.mountOptions)
 
 	if err := mount.Mount(info.DevName(), fsMountPoint, devices.BaseDeviceFilesystem, options); err != nil {
-		return fmt.Errorf("Error mounting '%s' on '%s': %s", info.DevName(), fsMountPoint, err)
+		return fmt.Errorf("Error mounting '%s' on '%s': %s\n%v", info.DevName(), fsMountPoint, err, string(dmesg.Dmesg(256)))
 	}
 
 	defer unix.Unmount(fsMountPoint, unix.MNT_DETACH)
@@ -2379,7 +2392,7 @@ func (devices *DeviceSet) MountDevice(hash, path, mountLabel string) error {
 	options = joinMountOptions(options, label.FormatMountLabel("", mountLabel))
 
 	if err := mount.Mount(info.DevName(), path, fstype, options); err != nil {
-		return fmt.Errorf("devmapper: Error mounting '%s' on '%s': %s", info.DevName(), path, err)
+		return fmt.Errorf("devmapper: Error mounting '%s' on '%s': %s\n%v", info.DevName(), path, err, string(dmesg.Dmesg(256)))
 	}
 
 	if fstype == "xfs" && devices.xfsNospaceRetries != "" {

daemon/graphdriver/register/register_devicemapper.go

@@ -1,4 +1,4 @@
-// +build !exclude_graphdriver_devicemapper,linux
+// +build !exclude_graphdriver_devicemapper,!static_build,linux
 
 package register
 

integration-cli/docker_cli_logs_test.go

@@ -214,14 +214,15 @@ func (s *DockerSuite) TestLogsSinceFutureFollow(c *check.C) {
 func (s *DockerSuite) TestLogsFollowSlowStdoutConsumer(c *check.C) {
 	// TODO Windows: Fix this test for TP5.
 	testRequires(c, DaemonIsLinux)
-	out, _ := dockerCmd(c, "run", "-d", "busybox", "/bin/sh", "-c", `usleep 600000;yes X | head -c 200000`)
+	expected := 150000
+	out, _ := dockerCmd(c, "run", "-d", "busybox", "/bin/sh", "-c", fmt.Sprintf("usleep 600000; yes X | head -c %d", expected))
 
 	id := strings.TrimSpace(out)
 
 	stopSlowRead := make(chan bool)
 
 	go func() {
-		exec.Command(dockerBinary, "wait", id).Run()
+		dockerCmd(c, "wait", id)
 		stopSlowRead <- true
 	}()
 
@@ -238,8 +239,9 @@ func (s *DockerSuite) TestLogsFollowSlowStdoutConsumer(c *check.C) {
 	bytes2, err := ConsumeWithSpeed(stdout, 32*1024, 0, nil)
 	c.Assert(err, checker.IsNil)
 
+	c.Assert(logCmd.Wait(), checker.IsNil)
+
 	actual := bytes1 + bytes2
-	expected := 200000
 	c.Assert(actual, checker.Equals, expected)
 }
 
@@ -288,6 +290,7 @@ func (s *DockerSuite) TestLogsFollowGoroutinesWithStdout(c *check.C) {
 	c.Assert(<-chErr, checker.IsNil)
 	c.Assert(cmd.Process.Kill(), checker.IsNil)
 	r.Close()
+	cmd.Wait()
 	// NGoroutines is not updated right away, so we need to wait before failing
 	c.Assert(waitForGoroutines(nroutines), checker.IsNil)
 }
@@ -303,6 +306,7 @@ func (s *DockerSuite) TestLogsFollowGoroutinesNoOutput(c *check.C) {
 	c.Assert(cmd.Start(), checker.IsNil)
 	time.Sleep(200 * time.Millisecond)
 	c.Assert(cmd.Process.Kill(), checker.IsNil)
+	cmd.Wait()
 
 	// NGoroutines is not updated right away, so we need to wait before failing
 	c.Assert(waitForGoroutines(nroutines), checker.IsNil)

integration-cli/docker_cli_run_unix_test.go

@@ -1060,7 +1060,7 @@ func (s *DockerSuite) TestRunSeccompProfileAllow32Bit(c *check.C) {
 	testRequires(c, SameHostDaemon, seccompEnabled, IsAmd64)
 	ensureSyscallTest(c)
 
-	icmd.RunCommand(dockerBinary, "run", "syscall-test", "exit32-test", "id").Assert(c, icmd.Success)
+	icmd.RunCommand(dockerBinary, "run", "syscall-test", "exit32-test").Assert(c, icmd.Success)
 }
 
 // TestRunSeccompAllowSetrlimit checks that 'docker run debian:jessie ulimit -v 1048510' succeeds.

integration-cli/fixtures_linux_daemon_test.go

@@ -57,7 +57,7 @@ func ensureSyscallTest(c *check.C) {
 	}
 
 	if runtime.GOOS == "linux" && runtime.GOARCH == "amd64" {
-		out, err := exec.Command(gcc, "-s", "-m32", "-nostdlib", "../contrib/syscall-test/exit32.s", "-o", tmp+"/"+"exit32-test").CombinedOutput()
+		out, err := exec.Command(gcc, "-s", "-m32", "-nostdlib", "-static", "../contrib/syscall-test/exit32.s", "-o", tmp+"/"+"exit32-test").CombinedOutput()
 		c.Assert(err, checker.IsNil, check.Commentf(string(out)))
 	}
 

pkg/devicemapper/devmapper_wrapper_static.go

@@ -1,6 +0,0 @@
-// +build linux,cgo,static_build
-
-package devicemapper
-
-// #cgo pkg-config: --static devmapper
-import "C"

pkg/dmesg/dmesg_linux.go

@@ -0,0 +1,20 @@
+// +build linux
+
+package dmesg
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// Dmesg returns last messages from the kernel log, up to size bytes
+func Dmesg(size int) []byte {
+	t := uintptr(3) // SYSLOG_ACTION_READ_ALL
+	b := make([]byte, size)
+	amt, _, err := unix.Syscall(unix.SYS_SYSLOG, t, uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)))
+	if err != 0 {
+		return []byte{}
+	}
+	return b[:amt]
+}

pkg/dmesg/dmesg_linux_test.go

@@ -0,0 +1,9 @@
+package dmesg
+
+import (
+	"testing"
+)
+
+func TestDmesg(t *testing.T) {
+	t.Logf("dmesg output follows:\n%v", string(Dmesg(512)))
+}