x/sys/plan9: implement the environment functions by wrapping syscall

Make Plan 9 implementation similar to Unix.

Fixes golang/go#10803.

Change-Id: Ib2f069a68370792daf926ec2a393f9cf16c2816b
Reviewed-on: https://go-review.googlesource.com/10104Reviewed-by: Rob Pike <r@golang.org>

plan9/env_plan9.go

@@ -7,168 +7,21 @@
 package plan9
 
 import (
-	"errors"
-	"sync"
+	"syscall"
 )
 
-var (
-	// envOnce guards copyenv, which populates env.
-	envOnce sync.Once
-
-	// envLock guards env and envs.
-	envLock sync.RWMutex
-
-	// env maps from an environment variable to its value.
-	env = make(map[string]string)
-
-	// envs contains elements of env in the form "key=value".
-	envs []string
-
-	errZeroLengthKey = errors.New("zero length key")
-	errShortWrite    = errors.New("i/o count too small")
-)
-
-func readenv(key string) (string, error) {
-	fd, err := open("/env/"+key, O_RDONLY)
-	if err != nil {
-		return "", err
-	}
-	defer Close(fd)
-	l, _ := Seek(fd, 0, 2)
-	Seek(fd, 0, 0)
-	buf := make([]byte, l)
-	n, err := Read(fd, buf)
-	if err != nil {
-		return "", err
-	}
-	if n > 0 && buf[n-1] == 0 {
-		buf = buf[:n-1]
-	}
-	return string(buf), nil
-}
-
-func writeenv(key, value string) error {
-	fd, err := create("/env/"+key, O_RDWR, 0666)
-	if err != nil {
-		return err
-	}
-	defer Close(fd)
-	b := []byte(value)
-	n, err := Write(fd, b)
-	if err != nil {
-		return err
-	}
-	if n != len(b) {
-		return errShortWrite
-	}
-	return nil
-}
-
-func copyenv() {
-	fd, err := open("/env", O_RDONLY)
-	if err != nil {
-		return
-	}
-	defer Close(fd)
-	files, err := readdirnames(fd)
-	if err != nil {
-		return
-	}
-	envs = make([]string, len(files))
-	i := 0
-	for _, key := range files {
-		v, err := readenv(key)
-		if err != nil {
-			continue
-		}
-		env[key] = v
-		envs[i] = key + "=" + v
-		i++
-	}
-}
-
-// readdirnames returns the names of files inside the directory represented by dirfd.
-func readdirnames(dirfd int) (names []string, err error) {
-	names = make([]string, 0, 100)
-	var buf [STATMAX]byte
-
-	for {
-		n, e := Read(dirfd, buf[:])
-		if e != nil {
-			return nil, e
-		}
-		if n == 0 {
-			break
-		}
-		for i := 0; i < n; {
-			m, _ := gbit16(buf[i:])
-			m += 2
-
-			if m < STATFIXLEN {
-				return nil, ErrBadStat
-			}
-
-			s, _, ok := gstring(buf[i+41:])
-			if !ok {
-				return nil, ErrBadStat
-			}
-			names = append(names, s)
-			i += int(m)
-		}
-	}
-	return
-}
-
 func Getenv(key string) (value string, found bool) {
-	if len(key) == 0 {
-		return "", false
-	}
-
-	envLock.RLock()
-	defer envLock.RUnlock()
-
-	if v, ok := env[key]; ok {
-		return v, true
-	}
-	v, err := readenv(key)
-	if err != nil {
-		return "", false
-	}
-	env[key] = v
-	envs = append(envs, key+"="+v)
-	return v, true
+	return syscall.Getenv(key)
 }
 
 func Setenv(key, value string) error {
-	if len(key) == 0 {
-		return errZeroLengthKey
-	}
-
-	envLock.Lock()
-	defer envLock.Unlock()
-
-	err := writeenv(key, value)
-	if err != nil {
-		return err
-	}
-	env[key] = value
-	envs = append(envs, key+"="+value)
-	return nil
+	return syscall.Setenv(key, value)
 }
 
 func Clearenv() {
-	envLock.Lock()
-	defer envLock.Unlock()
-
-	env = make(map[string]string)
-	envs = []string{}
-	RawSyscall(SYS_RFORK, RFCENVG, 0, 0)
+	syscall.Clearenv()
 }
 
 func Environ() []string {
-	envLock.RLock()
-	defer envLock.RUnlock()
-
-	envOnce.Do(copyenv)
-	return append([]string(nil), envs...)
+	return syscall.Environ()
 }