1 files changed, 122 insertions, 0 deletions
diff --git a/src/runtime/env_plan9.go b/src/runtime/env_plan9.go
new file mode 100644
index 0000000..f1ac476
--- /dev/null
+++ b/src/runtime/env_plan9.go
@@ -0,0 +1,122 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "unsafe"
+
+const (
+	// Plan 9 environment device
+	envDir = "/env/"
+	// size of buffer to read from a directory
+	dirBufSize = 4096
+	// size of buffer to read an environment variable (may grow)
+	envBufSize = 128
+	// offset of the name field in a 9P directory entry - see syscall.UnmarshalDir()
+	nameOffset = 39
+)
+
+// Goenvs caches the Plan 9 environment variables at start of execution into
+// string array envs, to supply the initial contents for os.Environ.
+// Subsequent calls to os.Setenv will change this cache, without writing back
+// to the (possibly shared) Plan 9 environment, so that Setenv and Getenv
+// conform to the same Posix semantics as on other operating systems.
+// For Plan 9 shared environment semantics, instead of Getenv(key) and
+// Setenv(key, value), one can use os.ReadFile("/env/" + key) and
+// os.WriteFile("/env/" + key, value, 0666) respectively.
+//go:nosplit
+func goenvs() {
+	buf := make([]byte, envBufSize)
+	copy(buf, envDir)
+	dirfd := open(&buf[0], _OREAD, 0)
+	if dirfd < 0 {
+		return
+	}
+	defer closefd(dirfd)
+	dofiles(dirfd, func(name []byte) {
+		name = append(name, 0)
+		buf = buf[:len(envDir)]
+		copy(buf, envDir)
+		buf = append(buf, name...)
+		fd := open(&buf[0], _OREAD, 0)
+		if fd < 0 {
+			return
+		}
+		defer closefd(fd)
+		n := len(buf)
+		r := 0
+		for {
+			r = int(pread(fd, unsafe.Pointer(&buf[0]), int32(n), 0))
+			if r < n {
+				break
+			}
+			n = int(seek(fd, 0, 2)) + 1
+			if len(buf) < n {
+				buf = make([]byte, n)
+			}
+		}
+		if r <= 0 {
+			r = 0
+		} else if buf[r-1] == 0 {
+			r--
+		}
+		name[len(name)-1] = '='
+		env := make([]byte, len(name)+r)
+		copy(env, name)
+		copy(env[len(name):], buf[:r])
+		envs = append(envs, string(env))
+	})
+}
+
+// Dofiles reads the directory opened with file descriptor fd, applying function f
+// to each filename in it.
+//go:nosplit
+func dofiles(dirfd int32, f func([]byte)) {
+	dirbuf := new([dirBufSize]byte)
+
+	var off int64 = 0
+	for {
+		n := pread(dirfd, unsafe.Pointer(&dirbuf[0]), int32(dirBufSize), off)
+		if n <= 0 {
+			return
+		}
+		for b := dirbuf[:n]; len(b) > 0; {
+			var name []byte
+			name, b = gdirname(b)
+			if name == nil {
+				return
+			}
+			f(name)
+		}
+		off += int64(n)
+	}
+}
+
+// Gdirname returns the first filename from a buffer of directory entries,
+// and a slice containing the remaining directory entries.
+// If the buffer doesn't start with a valid directory entry, the returned name is nil.
+//go:nosplit
+func gdirname(buf []byte) (name []byte, rest []byte) {
+	if 2+nameOffset+2 > len(buf) {
+		return
+	}
+	entryLen, buf := gbit16(buf)
+	if entryLen > len(buf) {
+		return
+	}
+	n, b := gbit16(buf[nameOffset:])
+	if n > len(b) {
+		return
+	}
+	name = b[:n]
+	rest = buf[entryLen:]
+	return
+}
+
+// Gbit16 reads a 16-bit little-endian binary number from b and returns it
+// with the remaining slice of b.
+//go:nosplit
+func gbit16(b []byte) (int, []byte) {
+	return int(b[0]) | int(b[1])<<8, b[2:]
+}