Add vendoring to containerd master

Initial vendor list validated with empty $GOPATH
and only master checked out; followed by `make`
and verified that all binaries build properly.
Updates require github.com/LK4D4/vndr tool.

Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com>

vendor/github.com/opencontainers/runc/libcontainer/system/linux.go

@@ -0,0 +1,143 @@
+// +build linux
+
+package system
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+	"unsafe"
+)
+
+// If arg2 is nonzero, set the "child subreaper" attribute of the
+// calling process; if arg2 is zero, unset the attribute.  When a
+// process is marked as a child subreaper, all of the children
+// that it creates, and their descendants, will be marked as
+// having a subreaper.  In effect, a subreaper fulfills the role
+// of init(1) for its descendant processes.  Upon termination of
+// a process that is orphaned (i.e., its immediate parent has
+// already terminated) and marked as having a subreaper, the
+// nearest still living ancestor subreaper will receive a SIGCHLD
+// signal and be able to wait(2) on the process to discover its
+// termination status.
+const PR_SET_CHILD_SUBREAPER = 36
+
+type ParentDeathSignal int
+
+func (p ParentDeathSignal) Restore() error {
+	if p == 0 {
+		return nil
+	}
+	current, err := GetParentDeathSignal()
+	if err != nil {
+		return err
+	}
+	if p == current {
+		return nil
+	}
+	return p.Set()
+}
+
+func (p ParentDeathSignal) Set() error {
+	return SetParentDeathSignal(uintptr(p))
+}
+
+func Execv(cmd string, args []string, env []string) error {
+	name, err := exec.LookPath(cmd)
+	if err != nil {
+		return err
+	}
+
+	return syscall.Exec(name, args, env)
+}
+
+func Prlimit(pid, resource int, limit syscall.Rlimit) error {
+	_, _, err := syscall.RawSyscall6(syscall.SYS_PRLIMIT64, uintptr(pid), uintptr(resource), uintptr(unsafe.Pointer(&limit)), uintptr(unsafe.Pointer(&limit)), 0, 0)
+	if err != 0 {
+		return err
+	}
+	return nil
+}
+
+func SetParentDeathSignal(sig uintptr) error {
+	if _, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, sig, 0); err != 0 {
+		return err
+	}
+	return nil
+}
+
+func GetParentDeathSignal() (ParentDeathSignal, error) {
+	var sig int
+	_, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_GET_PDEATHSIG, uintptr(unsafe.Pointer(&sig)), 0)
+	if err != 0 {
+		return -1, err
+	}
+	return ParentDeathSignal(sig), nil
+}
+
+func SetKeepCaps() error {
+	if _, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_KEEPCAPS, 1, 0); err != 0 {
+		return err
+	}
+
+	return nil
+}
+
+func ClearKeepCaps() error {
+	if _, _, err := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_KEEPCAPS, 0, 0); err != 0 {
+		return err
+	}
+
+	return nil
+}
+
+func Setctty() error {
+	if _, _, err := syscall.RawSyscall(syscall.SYS_IOCTL, 0, uintptr(syscall.TIOCSCTTY), 0); err != 0 {
+		return err
+	}
+	return nil
+}
+
+// RunningInUserNS detects whether we are currently running in a user namespace.
+// Copied from github.com/lxc/lxd/shared/util.go
+func RunningInUserNS() bool {
+	file, err := os.Open("/proc/self/uid_map")
+	if err != nil {
+		// This kernel-provided file only exists if user namespaces are supported
+		return false
+	}
+	defer file.Close()
+
+	buf := bufio.NewReader(file)
+	l, _, err := buf.ReadLine()
+	if err != nil {
+		return false
+	}
+
+	line := string(l)
+	var a, b, c int64
+	fmt.Sscanf(line, "%d %d %d", &a, &b, &c)
+	/*
+	 * We assume we are in the initial user namespace if we have a full
+	 * range - 4294967295 uids starting at uid 0.
+	 */
+	if a == 0 && b == 0 && c == 4294967295 {
+		return false
+	}
+	return true
+}
+
+// SetSubreaper sets the value i as the subreaper setting for the calling process
+func SetSubreaper(i int) error {
+	return Prctl(PR_SET_CHILD_SUBREAPER, uintptr(i), 0, 0, 0)
+}
+
+func Prctl(option int, arg2, arg3, arg4, arg5 uintptr) (err error) {
+	_, _, e1 := syscall.Syscall6(syscall.SYS_PRCTL, uintptr(option), arg2, arg3, arg4, arg5, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}

vendor/github.com/opencontainers/runc/libcontainer/system/proc.go

@@ -0,0 +1,27 @@
+package system
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// look in /proc to find the process start time so that we can verify
+// that this pid has started after ourself
+func GetProcessStartTime(pid int) (string, error) {
+	data, err := ioutil.ReadFile(filepath.Join("/proc", strconv.Itoa(pid), "stat"))
+	if err != nil {
+		return "", err
+	}
+
+	parts := strings.Split(string(data), " ")
+	// the starttime is located at pos 22
+	// from the man page
+	//
+	// starttime %llu (was %lu before Linux 2.6)
+	// (22)  The  time the process started after system boot.  In kernels before Linux 2.6, this
+	// value was expressed in jiffies.  Since Linux 2.6, the value is expressed in  clock  ticks
+	// (divide by sysconf(_SC_CLK_TCK)).
+	return parts[22-1], nil // starts at 1
+}

vendor/github.com/opencontainers/runc/libcontainer/system/setns_linux.go

@@ -0,0 +1,40 @@
+package system
+
+import (
+	"fmt"
+	"runtime"
+	"syscall"
+)
+
+// Via http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7b21fddd087678a70ad64afc0f632e0f1071b092
+//
+// We need different setns values for the different platforms and arch
+// We are declaring the macro here because the SETNS syscall does not exist in th stdlib
+var setNsMap = map[string]uintptr{
+	"linux/386":     346,
+	"linux/arm64":   268,
+	"linux/amd64":   308,
+	"linux/arm":     375,
+	"linux/ppc":     350,
+	"linux/ppc64":   350,
+	"linux/ppc64le": 350,
+	"linux/s390x":   339,
+}
+
+var sysSetns = setNsMap[fmt.Sprintf("%s/%s", runtime.GOOS, runtime.GOARCH)]
+
+func SysSetns() uint32 {
+	return uint32(sysSetns)
+}
+
+func Setns(fd uintptr, flags uintptr) error {
+	ns, exists := setNsMap[fmt.Sprintf("%s/%s", runtime.GOOS, runtime.GOARCH)]
+	if !exists {
+		return fmt.Errorf("unsupported platform %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+	_, _, err := syscall.RawSyscall(ns, fd, flags, 0)
+	if err != 0 {
+		return err
+	}
+	return nil
+}

vendor/github.com/opencontainers/runc/libcontainer/system/syscall_linux_386.go

@@ -0,0 +1,25 @@
+// +build linux,386
+
+package system
+
+import (
+	"syscall"
+)
+
+// Setuid sets the uid of the calling thread to the specified uid.
+func Setuid(uid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETUID32, uintptr(uid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// Setgid sets the gid of the calling thread to the specified gid.
+func Setgid(gid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETGID32, uintptr(gid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}

vendor/github.com/opencontainers/runc/libcontainer/system/syscall_linux_64.go

@@ -0,0 +1,25 @@
+// +build linux,arm64 linux,amd64 linux,ppc linux,ppc64 linux,ppc64le linux,s390x
+
+package system
+
+import (
+	"syscall"
+)
+
+// Setuid sets the uid of the calling thread to the specified uid.
+func Setuid(uid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETUID, uintptr(uid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// Setgid sets the gid of the calling thread to the specified gid.
+func Setgid(gid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETGID, uintptr(gid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}

vendor/github.com/opencontainers/runc/libcontainer/system/syscall_linux_arm.go

@@ -0,0 +1,25 @@
+// +build linux,arm
+
+package system
+
+import (
+	"syscall"
+)
+
+// Setuid sets the uid of the calling thread to the specified uid.
+func Setuid(uid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETUID32, uintptr(uid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}
+
+// Setgid sets the gid of the calling thread to the specified gid.
+func Setgid(gid int) (err error) {
+	_, _, e1 := syscall.RawSyscall(syscall.SYS_SETGID32, uintptr(gid), 0, 0)
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}

vendor/github.com/opencontainers/runc/libcontainer/system/sysconfig.go

@@ -0,0 +1,12 @@
+// +build cgo,linux cgo,freebsd
+
+package system
+
+/*
+#include <unistd.h>
+*/
+import "C"
+
+func GetClockTicks() int {
+	return int(C.sysconf(C._SC_CLK_TCK))
+}

vendor/github.com/opencontainers/runc/libcontainer/system/sysconfig_notcgo.go

@@ -0,0 +1,15 @@
+// +build !cgo windows
+
+package system
+
+func GetClockTicks() int {
+	// TODO figure out a better alternative for platforms where we're missing cgo
+	//
+	// TODO Windows. This could be implemented using Win32 QueryPerformanceFrequency().
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx
+	//
+	// An example of its usage can be found here.
+	// https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx
+
+	return 100
+}

vendor/github.com/opencontainers/runc/libcontainer/system/unsupported.go

@@ -0,0 +1,9 @@
+// +build !linux
+
+package system
+
+// RunningInUserNS is a stub for non-Linux systems
+// Always returns false
+func RunningInUserNS() bool {
+	return false
+}

vendor/github.com/opencontainers/runc/libcontainer/system/xattrs_linux.go

@@ -0,0 +1,99 @@
+package system
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+var _zero uintptr
+
+// Returns the size of xattrs and nil error
+// Requires path, takes allocated []byte or nil as last argument
+func Llistxattr(path string, dest []byte) (size int, err error) {
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return -1, err
+	}
+	var newpathBytes unsafe.Pointer
+	if len(dest) > 0 {
+		newpathBytes = unsafe.Pointer(&dest[0])
+	} else {
+		newpathBytes = unsafe.Pointer(&_zero)
+	}
+
+	_size, _, errno := syscall.Syscall6(syscall.SYS_LLISTXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(newpathBytes), uintptr(len(dest)), 0, 0, 0)
+	size = int(_size)
+	if errno != 0 {
+		return -1, errno
+	}
+
+	return size, nil
+}
+
+// Returns a []byte slice if the xattr is set and nil otherwise
+// Requires path and its attribute as arguments
+func Lgetxattr(path string, attr string) ([]byte, error) {
+	var sz int
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return nil, err
+	}
+	attrBytes, err := syscall.BytePtrFromString(attr)
+	if err != nil {
+		return nil, err
+	}
+
+	// Start with a 128 length byte array
+	sz = 128
+	dest := make([]byte, sz)
+	destBytes := unsafe.Pointer(&dest[0])
+	_sz, _, errno := syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
+
+	switch {
+	case errno == syscall.ENODATA:
+		return nil, errno
+	case errno == syscall.ENOTSUP:
+		return nil, errno
+	case errno == syscall.ERANGE:
+		// 128 byte array might just not be good enough,
+		// A dummy buffer is used ``uintptr(0)`` to get real size
+		// of the xattrs on disk
+		_sz, _, errno = syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(unsafe.Pointer(nil)), uintptr(0), 0, 0)
+		sz = int(_sz)
+		if sz < 0 {
+			return nil, errno
+		}
+		dest = make([]byte, sz)
+		destBytes := unsafe.Pointer(&dest[0])
+		_sz, _, errno = syscall.Syscall6(syscall.SYS_LGETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(destBytes), uintptr(len(dest)), 0, 0)
+		if errno != 0 {
+			return nil, errno
+		}
+	case errno != 0:
+		return nil, errno
+	}
+	sz = int(_sz)
+	return dest[:sz], nil
+}
+
+func Lsetxattr(path string, attr string, data []byte, flags int) error {
+	pathBytes, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	attrBytes, err := syscall.BytePtrFromString(attr)
+	if err != nil {
+		return err
+	}
+	var dataBytes unsafe.Pointer
+	if len(data) > 0 {
+		dataBytes = unsafe.Pointer(&data[0])
+	} else {
+		dataBytes = unsafe.Pointer(&_zero)
+	}
+	_, _, errno := syscall.Syscall6(syscall.SYS_LSETXATTR, uintptr(unsafe.Pointer(pathBytes)), uintptr(unsafe.Pointer(attrBytes)), uintptr(dataBytes), uintptr(len(data)), uintptr(flags), 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}

vendor/github.com/opencontainers/runc/libcontainer/user/lookup.go

@@ -0,0 +1,110 @@
+package user
+
+import (
+	"errors"
+	"syscall"
+)
+
+var (
+	// The current operating system does not provide the required data for user lookups.
+	ErrUnsupported = errors.New("user lookup: operating system does not provide passwd-formatted data")
+	// No matching entries found in file.
+	ErrNoPasswdEntries = errors.New("no matching entries in passwd file")
+	ErrNoGroupEntries  = errors.New("no matching entries in group file")
+)
+
+func lookupUser(filter func(u User) bool) (User, error) {
+	// Get operating system-specific passwd reader-closer.
+	passwd, err := GetPasswd()
+	if err != nil {
+		return User{}, err
+	}
+	defer passwd.Close()
+
+	// Get the users.
+	users, err := ParsePasswdFilter(passwd, filter)
+	if err != nil {
+		return User{}, err
+	}
+
+	// No user entries found.
+	if len(users) == 0 {
+		return User{}, ErrNoPasswdEntries
+	}
+
+	// Assume the first entry is the "correct" one.
+	return users[0], nil
+}
+
+// CurrentUser looks up the current user by their user id in /etc/passwd. If the
+// user cannot be found (or there is no /etc/passwd file on the filesystem),
+// then CurrentUser returns an error.
+func CurrentUser() (User, error) {
+	return LookupUid(syscall.Getuid())
+}
+
+// LookupUser looks up a user by their username in /etc/passwd. If the user
+// cannot be found (or there is no /etc/passwd file on the filesystem), then
+// LookupUser returns an error.
+func LookupUser(username string) (User, error) {
+	return lookupUser(func(u User) bool {
+		return u.Name == username
+	})
+}
+
+// LookupUid looks up a user by their user id in /etc/passwd. If the user cannot
+// be found (or there is no /etc/passwd file on the filesystem), then LookupId
+// returns an error.
+func LookupUid(uid int) (User, error) {
+	return lookupUser(func(u User) bool {
+		return u.Uid == uid
+	})
+}
+
+func lookupGroup(filter func(g Group) bool) (Group, error) {
+	// Get operating system-specific group reader-closer.
+	group, err := GetGroup()
+	if err != nil {
+		return Group{}, err
+	}
+	defer group.Close()
+
+	// Get the users.
+	groups, err := ParseGroupFilter(group, filter)
+	if err != nil {
+		return Group{}, err
+	}
+
+	// No user entries found.
+	if len(groups) == 0 {
+		return Group{}, ErrNoGroupEntries
+	}
+
+	// Assume the first entry is the "correct" one.
+	return groups[0], nil
+}
+
+// CurrentGroup looks up the current user's group by their primary group id's
+// entry in /etc/passwd. If the group cannot be found (or there is no
+// /etc/group file on the filesystem), then CurrentGroup returns an error.
+func CurrentGroup() (Group, error) {
+	return LookupGid(syscall.Getgid())
+}
+
+// LookupGroup looks up a group by its name in /etc/group. If the group cannot
+// be found (or there is no /etc/group file on the filesystem), then LookupGroup
+// returns an error.
+func LookupGroup(groupname string) (Group, error) {
+	return lookupGroup(func(g Group) bool {
+		return g.Name == groupname
+	})
+}
+
+// LookupGid looks up a group by its group id in /etc/group. If the group cannot
+// be found (or there is no /etc/group file on the filesystem), then LookupGid
+// returns an error.
+func LookupGid(gid int) (Group, error) {
+	return lookupGroup(func(g Group) bool {
+		return g.Gid == gid
+	})
+}

vendor/github.com/opencontainers/runc/libcontainer/user/lookup_unix.go

@@ -0,0 +1,30 @@
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package user
+
+import (
+	"io"
+	"os"
+)
+
+// Unix-specific path to the passwd and group formatted files.
+const (
+	unixPasswdPath = "/etc/passwd"
+	unixGroupPath  = "/etc/group"
+)
+
+func GetPasswdPath() (string, error) {
+	return unixPasswdPath, nil
+}
+
+func GetPasswd() (io.ReadCloser, error) {
+	return os.Open(unixPasswdPath)
+}
+
+func GetGroupPath() (string, error) {
+	return unixGroupPath, nil
+}
+
+func GetGroup() (io.ReadCloser, error) {
+	return os.Open(unixGroupPath)
+}

vendor/github.com/opencontainers/runc/libcontainer/user/lookup_unsupported.go

@@ -0,0 +1,21 @@
+// +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris
+
+package user
+
+import "io"
+
+func GetPasswdPath() (string, error) {
+	return "", ErrUnsupported
+}
+
+func GetPasswd() (io.ReadCloser, error) {
+	return nil, ErrUnsupported
+}
+
+func GetGroupPath() (string, error) {
+	return "", ErrUnsupported
+}
+
+func GetGroup() (io.ReadCloser, error) {
+	return nil, ErrUnsupported
+}

vendor/github.com/opencontainers/runc/libcontainer/user/user.go

@@ -0,0 +1,441 @@
+package user
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const (
+	minId = 0
+	maxId = 1<<31 - 1 //for 32-bit systems compatibility
+)
+
+var (
+	ErrRange = fmt.Errorf("uids and gids must be in range %d-%d", minId, maxId)
+)
+
+type User struct {
+	Name  string
+	Pass  string
+	Uid   int
+	Gid   int
+	Gecos string
+	Home  string
+	Shell string
+}
+
+type Group struct {
+	Name string
+	Pass string
+	Gid  int
+	List []string
+}
+
+func parseLine(line string, v ...interface{}) {
+	if line == "" {
+		return
+	}
+
+	parts := strings.Split(line, ":")
+	for i, p := range parts {
+		// Ignore cases where we don't have enough fields to populate the arguments.
+		// Some configuration files like to misbehave.
+		if len(v) <= i {
+			break
+		}
+
+		// Use the type of the argument to figure out how to parse it, scanf() style.
+		// This is legit.
+		switch e := v[i].(type) {
+		case *string:
+			*e = p
+		case *int:
+			// "numbers", with conversion errors ignored because of some misbehaving configuration files.
+			*e, _ = strconv.Atoi(p)
+		case *[]string:
+			// Comma-separated lists.
+			if p != "" {
+				*e = strings.Split(p, ",")
+			} else {
+				*e = []string{}
+			}
+		default:
+			// Someone goof'd when writing code using this function. Scream so they can hear us.
+			panic(fmt.Sprintf("parseLine only accepts {*string, *int, *[]string} as arguments! %#v is not a pointer!", e))
+		}
+	}
+}
+
+func ParsePasswdFile(path string) ([]User, error) {
+	passwd, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer passwd.Close()
+	return ParsePasswd(passwd)
+}
+
+func ParsePasswd(passwd io.Reader) ([]User, error) {
+	return ParsePasswdFilter(passwd, nil)
+}
+
+func ParsePasswdFileFilter(path string, filter func(User) bool) ([]User, error) {
+	passwd, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer passwd.Close()
+	return ParsePasswdFilter(passwd, filter)
+}
+
+func ParsePasswdFilter(r io.Reader, filter func(User) bool) ([]User, error) {
+	if r == nil {
+		return nil, fmt.Errorf("nil source for passwd-formatted data")
+	}
+
+	var (
+		s   = bufio.NewScanner(r)
+		out = []User{}
+	)
+
+	for s.Scan() {
+		if err := s.Err(); err != nil {
+			return nil, err
+		}
+
+		line := strings.TrimSpace(s.Text())
+		if line == "" {
+			continue
+		}
+
+		// see: man 5 passwd
+		//  name:password:UID:GID:GECOS:directory:shell
+		// Name:Pass:Uid:Gid:Gecos:Home:Shell
+		//  root:x:0:0:root:/root:/bin/bash
+		//  adm:x:3:4:adm:/var/adm:/bin/false
+		p := User{}
+		parseLine(line, &p.Name, &p.Pass, &p.Uid, &p.Gid, &p.Gecos, &p.Home, &p.Shell)
+
+		if filter == nil || filter(p) {
+			out = append(out, p)
+		}
+	}
+
+	return out, nil
+}
+
+func ParseGroupFile(path string) ([]Group, error) {
+	group, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	defer group.Close()
+	return ParseGroup(group)
+}
+
+func ParseGroup(group io.Reader) ([]Group, error) {
+	return ParseGroupFilter(group, nil)
+}
+
+func ParseGroupFileFilter(path string, filter func(Group) bool) ([]Group, error) {
+	group, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer group.Close()
+	return ParseGroupFilter(group, filter)
+}
+
+func ParseGroupFilter(r io.Reader, filter func(Group) bool) ([]Group, error) {
+	if r == nil {
+		return nil, fmt.Errorf("nil source for group-formatted data")
+	}
+
+	var (
+		s   = bufio.NewScanner(r)
+		out = []Group{}
+	)
+
+	for s.Scan() {
+		if err := s.Err(); err != nil {
+			return nil, err
+		}
+
+		text := s.Text()
+		if text == "" {
+			continue
+		}
+
+		// see: man 5 group
+		//  group_name:password:GID:user_list
+		// Name:Pass:Gid:List
+		//  root:x:0:root
+		//  adm:x:4:root,adm,daemon
+		p := Group{}
+		parseLine(text, &p.Name, &p.Pass, &p.Gid, &p.List)
+
+		if filter == nil || filter(p) {
+			out = append(out, p)
+		}
+	}
+
+	return out, nil
+}
+
+type ExecUser struct {
+	Uid   int
+	Gid   int
+	Sgids []int
+	Home  string
+}
+
+// GetExecUserPath is a wrapper for GetExecUser. It reads data from each of the
+// given file paths and uses that data as the arguments to GetExecUser. If the
+// files cannot be opened for any reason, the error is ignored and a nil
+// io.Reader is passed instead.
+func GetExecUserPath(userSpec string, defaults *ExecUser, passwdPath, groupPath string) (*ExecUser, error) {
+	passwd, err := os.Open(passwdPath)
+	if err != nil {
+		passwd = nil
+	} else {
+		defer passwd.Close()
+	}
+
+	group, err := os.Open(groupPath)
+	if err != nil {
+		group = nil
+	} else {
+		defer group.Close()
+	}
+
+	return GetExecUser(userSpec, defaults, passwd, group)
+}
+
+// GetExecUser parses a user specification string (using the passwd and group
+// readers as sources for /etc/passwd and /etc/group data, respectively). In
+// the case of blank fields or missing data from the sources, the values in
+// defaults is used.
+//
+// GetExecUser will return an error if a user or group literal could not be
+// found in any entry in passwd and group respectively.
+//
+// Examples of valid user specifications are:
+//     * ""
+//     * "user"
+//     * "uid"
+//     * "user:group"
+//     * "uid:gid
+//     * "user:gid"
+//     * "uid:group"
+//
+// It should be noted that if you specify a numeric user or group id, they will
+// not be evaluated as usernames (only the metadata will be filled). So attempting
+// to parse a user with user.Name = "1337" will produce the user with a UID of
+// 1337.
+func GetExecUser(userSpec string, defaults *ExecUser, passwd, group io.Reader) (*ExecUser, error) {
+	if defaults == nil {
+		defaults = new(ExecUser)
+	}
+
+	// Copy over defaults.
+	user := &ExecUser{
+		Uid:   defaults.Uid,
+		Gid:   defaults.Gid,
+		Sgids: defaults.Sgids,
+		Home:  defaults.Home,
+	}
+
+	// Sgids slice *cannot* be nil.
+	if user.Sgids == nil {
+		user.Sgids = []int{}
+	}
+
+	// Allow for userArg to have either "user" syntax, or optionally "user:group" syntax
+	var userArg, groupArg string
+	parseLine(userSpec, &userArg, &groupArg)
+
+	// Convert userArg and groupArg to be numeric, so we don't have to execute
+	// Atoi *twice* for each iteration over lines.
+	uidArg, uidErr := strconv.Atoi(userArg)
+	gidArg, gidErr := strconv.Atoi(groupArg)
+
+	// Find the matching user.
+	users, err := ParsePasswdFilter(passwd, func(u User) bool {
+		if userArg == "" {
+			// Default to current state of the user.
+			return u.Uid == user.Uid
+		}
+
+		if uidErr == nil {
+			// If the userArg is numeric, always treat it as a UID.
+			return uidArg == u.Uid
+		}
+
+		return u.Name == userArg
+	})
+
+	// If we can't find the user, we have to bail.
+	if err != nil && passwd != nil {
+		if userArg == "" {
+			userArg = strconv.Itoa(user.Uid)
+		}
+		return nil, fmt.Errorf("unable to find user %s: %v", userArg, err)
+	}
+
+	var matchedUserName string
+	if len(users) > 0 {
+		// First match wins, even if there's more than one matching entry.
+		matchedUserName = users[0].Name
+		user.Uid = users[0].Uid
+		user.Gid = users[0].Gid
+		user.Home = users[0].Home
+	} else if userArg != "" {
+		// If we can't find a user with the given username, the only other valid
+		// option is if it's a numeric username with no associated entry in passwd.
+
+		if uidErr != nil {
+			// Not numeric.
+			return nil, fmt.Errorf("unable to find user %s: %v", userArg, ErrNoPasswdEntries)
+		}
+		user.Uid = uidArg
+
+		// Must be inside valid uid range.
+		if user.Uid < minId || user.Uid > maxId {
+			return nil, ErrRange
+		}
+
+		// Okay, so it's numeric. We can just roll with this.
+	}
+
+	// On to the groups. If we matched a username, we need to do this because of
+	// the supplementary group IDs.
+	if groupArg != "" || matchedUserName != "" {
+		groups, err := ParseGroupFilter(group, func(g Group) bool {
+			// If the group argument isn't explicit, we'll just search for it.
+			if groupArg == "" {
+				// Check if user is a member of this group.
+				for _, u := range g.List {
+					if u == matchedUserName {
+						return true
+					}
+				}
+				return false
+			}
+
+			if gidErr == nil {
+				// If the groupArg is numeric, always treat it as a GID.
+				return gidArg == g.Gid
+			}
+
+			return g.Name == groupArg
+		})
+		if err != nil && group != nil {
+			return nil, fmt.Errorf("unable to find groups for spec %v: %v", matchedUserName, err)
+		}
+
+		// Only start modifying user.Gid if it is in explicit form.
+		if groupArg != "" {
+			if len(groups) > 0 {
+				// First match wins, even if there's more than one matching entry.
+				user.Gid = groups[0].Gid
+			} else if groupArg != "" {
+				// If we can't find a group with the given name, the only other valid
+				// option is if it's a numeric group name with no associated entry in group.
+
+				if gidErr != nil {
+					// Not numeric.
+					return nil, fmt.Errorf("unable to find group %s: %v", groupArg, ErrNoGroupEntries)
+				}
+				user.Gid = gidArg
+
+				// Must be inside valid gid range.
+				if user.Gid < minId || user.Gid > maxId {
+					return nil, ErrRange
+				}
+
+				// Okay, so it's numeric. We can just roll with this.
+			}
+		} else if len(groups) > 0 {
+			// Supplementary group ids only make sense if in the implicit form.
+			user.Sgids = make([]int, len(groups))
+			for i, group := range groups {
+				user.Sgids[i] = group.Gid
+			}
+		}
+	}
+
+	return user, nil
+}
+
+// GetAdditionalGroups looks up a list of groups by name or group id
+// against the given /etc/group formatted data. If a group name cannot
+// be found, an error will be returned. If a group id cannot be found,
+// or the given group data is nil, the id will be returned as-is
+// provided it is in the legal range.
+func GetAdditionalGroups(additionalGroups []string, group io.Reader) ([]int, error) {
+	var groups = []Group{}
+	if group != nil {
+		var err error
+		groups, err = ParseGroupFilter(group, func(g Group) bool {
+			for _, ag := range additionalGroups {
+				if g.Name == ag || strconv.Itoa(g.Gid) == ag {
+					return true
+				}
+			}
+			return false
+		})
+		if err != nil {
+			return nil, fmt.Errorf("Unable to find additional groups %v: %v", additionalGroups, err)
+		}
+	}
+
+	gidMap := make(map[int]struct{})
+	for _, ag := range additionalGroups {
+		var found bool
+		for _, g := range groups {
+			// if we found a matched group either by name or gid, take the
+			// first matched as correct
+			if g.Name == ag || strconv.Itoa(g.Gid) == ag {
+				if _, ok := gidMap[g.Gid]; !ok {
+					gidMap[g.Gid] = struct{}{}
+					found = true
+					break
+				}
+			}
+		}
+		// we asked for a group but didn't find it. let's check to see
+		// if we wanted a numeric group
+		if !found {
+			gid, err := strconv.Atoi(ag)
+			if err != nil {
+				return nil, fmt.Errorf("Unable to find group %s", ag)
+			}
+			// Ensure gid is inside gid range.
+			if gid < minId || gid > maxId {
+				return nil, ErrRange
+			}
+			gidMap[gid] = struct{}{}
+		}
+	}
+	gids := []int{}
+	for gid := range gidMap {
+		gids = append(gids, gid)
+	}
+	return gids, nil
+}
+
+// GetAdditionalGroupsPath is a wrapper around GetAdditionalGroups
+// that opens the groupPath given and gives it as an argument to
+// GetAdditionalGroups.
+func GetAdditionalGroupsPath(additionalGroups []string, groupPath string) ([]int, error) {
+	group, err := os.Open(groupPath)
+	if err == nil {
+		defer group.Close()
+	}
+	return GetAdditionalGroups(additionalGroups, group)
+}