WASI & darwin: support basic file io based on libc

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

main_test.go

@@ -59,7 +59,10 @@ func TestCompiler(t *testing.T) {
 		t.Run("Host", func(t *testing.T) {
 			runPlatTests("", matches, t)
 			if runtime.GOOS == "darwin" {
-				runTest("testdata/libc/env.go", "", t, []string{"ENV1=VALUE1", "ENV2=VALUE2"}...)
+				runTest("testdata/libc/filesystem.go", "", t,
+					nil, nil)
+				runTest("testdata/libc/env.go", "", t,
+					[]string{"ENV1=VALUE1", "ENV2=VALUE2"}, nil)
 			}
 		})
 	}
@@ -107,7 +110,9 @@ func TestCompiler(t *testing.T) {
 
 		t.Run("WASI", func(t *testing.T) {
 			runPlatTests("wasi", matches, t)
-			runTest("testdata/libc/env.go", "wasi", t, []string{"ENV1=VALUE1", "ENV2=VALUE2"}...)
+			runTest("testdata/libc/env.go", "wasi", t,
+				[]string{"--env", "ENV1=VALUE1", "--env", "ENV2=VALUE2"}, nil)
+			runTest("testdata/libc/filesystem.go", "wasi", t, nil, []string{"--dir=."})
 		})
 	}
 }
@@ -119,7 +124,7 @@ func runPlatTests(target string, matches []string, t *testing.T) {
 		path := path // redefine to avoid race condition
 		t.Run(filepath.Base(path), func(t *testing.T) {
 			t.Parallel()
-			runTest(path, target, t)
+			runTest(path, target, t, nil, nil)
 		})
 	}
 }
@@ -136,7 +141,7 @@ func runBuild(src, out string, opts *compileopts.Options) error {
 	return Build(src, out, opts)
 }
 
-func runTest(path, target string, t *testing.T, environmentVars ...string) {
+func runTest(path, target string, t *testing.T, environmentVars []string, additionalArgs []string) {
 	// Get the expected output for this test.
 	txtpath := path[:len(path)-3] + ".txt"
 	if path[len(path)-1] == os.PathSeparator {
@@ -195,7 +200,7 @@ func runTest(path, target string, t *testing.T, environmentVars ...string) {
 			cmd = exec.Command(binary)
 		} else {
 			args := append(spec.Emulator[1:], binary)
-			cmd = exec.Command(spec.Emulator[0], args...)
+			cmd = exec.Command(spec.Emulator[0], append(args, additionalArgs...)...)
 		}
 
 		if len(spec.Emulator) != 0 && spec.Emulator[0] == "wasmtime" {

src/os/errors.go

@@ -2,6 +2,7 @@ package os
 
 import (
 	"errors"
+	"syscall"
 )
 
 var (
@@ -17,9 +18,8 @@ var (
 	ErrExist          = errors.New("file exists")
 )
 
-func IsPermission(err error) bool {
-	return err == ErrPermission
-}
+// The following code is copied from the official implementation.
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/error.go#L65-L104
 
 func NewSyscallError(syscall string, err error) error {
 	if err == nil {
@@ -37,3 +37,39 @@ type SyscallError struct {
 func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
 
 func (e *SyscallError) Unwrap() error { return e.Err }
+
+func IsExist(err error) bool {
+	return underlyingErrorIs(err, ErrExist)
+}
+
+func IsNotExist(err error) bool {
+	return underlyingErrorIs(err, ErrNotExist)
+}
+
+func IsPermission(err error) bool {
+	return underlyingErrorIs(err, ErrPermission)
+}
+
+func underlyingErrorIs(err, target error) bool {
+	// Note that this function is not errors.Is:
+	// underlyingError only unwraps the specific error-wrapping types
+	// that it historically did, not all errors implementing Unwrap().
+	err = underlyingError(err)
+	if err == target {
+		return true
+	}
+	// To preserve prior behavior, only examine syscall errors.
+	e, ok := err.(syscall.Errno)
+	return ok && e.Is(target)
+}
+
+// underlyingError returns the underlying error for known os error types.
+func underlyingError(err error) error {
+	switch err := err.(type) {
+	case *PathError:
+		return err.Err
+	case *SyscallError:
+		return err.Err
+	}
+	return err
+}

src/os/file.go

@@ -6,6 +6,7 @@
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -76,7 +77,7 @@ func Create(name string) (*File, error) {
 // read and any error encountered. At end of file, Read returns 0, io.EOF.
 func (f *File) Read(b []byte) (n int, err error) {
 	n, err = f.handle.Read(b)
-	if err != nil {
+	if err != nil && err != io.EOF {
 		err = &PathError{"read", f.name, err}
 	}
 	return
@@ -155,59 +156,17 @@ func (e *PathError) Error() string {
 	return e.Op + " " + e.Path + ": " + e.Err.Error()
 }
 
-type FileMode uint32
-
-// Mode constants, copied from the mainline Go source
-// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
 const (
-	// The single letters are the abbreviations used by the String method's formatting.
-	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
-	ModeAppend                                     // a: append-only
-	ModeExclusive                                  // l: exclusive use
-	ModeTemporary                                  // T: temporary file; Plan 9 only
-	ModeSymlink                                    // L: symbolic link
-	ModeDevice                                     // D: device file
-	ModeNamedPipe                                  // p: named pipe (FIFO)
-	ModeSocket                                     // S: Unix domain socket
-	ModeSetuid                                     // u: setuid
-	ModeSetgid                                     // g: setgid
-	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
-	ModeSticky                                     // t: sticky
-	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
-
-	// Mask for the type bits. For regular files, none will be set.
-	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
-
-	ModePerm FileMode = 0777 // Unix permission bits
+	O_RDONLY int = syscall.O_RDONLY
+	O_WRONLY int = syscall.O_WRONLY
+	O_RDWR   int = syscall.O_RDWR
+	O_APPEND int = syscall.O_APPEND
+	O_CREATE int = syscall.O_CREAT
+	O_EXCL   int = syscall.O_EXCL
+	O_SYNC   int = syscall.O_SYNC
+	O_TRUNC  int = syscall.O_TRUNC
 )
 
-// IsDir is a stub, always returning false
-func (m FileMode) IsDir() bool {
-	return false
-}
-
-// Stub constants
-const (
-	O_RDONLY int = 1
-	O_WRONLY int = 2
-	O_RDWR   int = 4
-	O_APPEND int = 8
-	O_CREATE int = 16
-	O_EXCL   int = 32
-	O_SYNC   int = 64
-	O_TRUNC  int = 128
-)
-
-// A FileInfo describes a file and is returned by Stat and Lstat.
-type FileInfo interface {
-	Name() string   // base name of the file
-	Size() int64    // length in bytes for regular files; system-dependent for others
-	Mode() FileMode // file mode bits
-	// TODO ModTime() time.Time // modification time
-	IsDir() bool      // abbreviation for Mode().IsDir()
-	Sys() interface{} // underlying data source (can return nil)
-}
-
 // Stat is a stub, not yet implemented
 func Stat(name string) (FileInfo, error) {
 	return nil, &PathError{"stat", name, ErrNotImplemented}
@@ -233,16 +192,6 @@ func TempDir() string {
 	return "/tmp"
 }
 
-// IsExist is a stub (for now), always returning false
-func IsExist(err error) bool {
-	return false
-}
-
-// IsNotExist is a stub (for now), always returning false
-func IsNotExist(err error) bool {
-	return false
-}
-
 // Getpid is a stub (for now), always returning 1
 func Getpid() int {
 	return 1

src/os/file_go_116.go

@@ -0,0 +1,81 @@
+// +build go1.16
+
+package os
+
+import (
+	"io"
+	"io/fs"
+)
+
+type (
+	DirEntry = fs.DirEntry
+	FileMode = fs.FileMode
+	FileInfo = fs.FileInfo
+)
+
+func (f *File) ReadDir(n int) ([]DirEntry, error) {
+	return nil, &PathError{"ReadDir", f.name, ErrNotImplemented}
+}
+
+// The followings are copied from Go 1.16 official implementation:
+// https://github.com/golang/go/blob/go1.16/src/os/file.go
+
+// ReadFile reads the named file and returns the contents.
+// A successful call returns err == nil, not err == EOF.
+// Because ReadFile reads the whole file, it does not treat an EOF from Read
+// as an error to be reported.
+func ReadFile(name string) ([]byte, error) {
+	f, err := Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var size int
+	if info, err := f.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+	}
+	size++ // one byte for final read at EOF
+
+	// If a file claims a small size, read at least 512 bytes.
+	// In particular, files in Linux's /proc claim size 0 but
+	// then do not work right if read in small pieces,
+	// so an initial read of 1 byte would not work correctly.
+	if size < 512 {
+		size = 512
+	}
+
+	data := make([]byte, 0, size)
+	for {
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := f.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			return data, err
+		}
+	}
+}
+
+// WriteFile writes data to the named file, creating it if necessary.
+// If the file does not exist, WriteFile creates it with permissions perm (before umask);
+// otherwise WriteFile truncates it before writing, without changing permissions.
+func WriteFile(name string, data []byte, perm FileMode) error {
+	f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err1 := f.Close(); err1 != nil && err == nil {
+		err = err1
+	}
+	return err
+}

src/os/file_go_other.go

@@ -0,0 +1,46 @@
+// +build !go1.16
+
+package os
+
+import "time"
+
+// A FileInfo describes a file and is returned by Stat and Lstat.
+type FileInfo interface {
+	Name() string       // base name of the file
+	Size() int64        // length in bytes for regular files; system-dependent for others
+	Mode() FileMode     // file mode bits
+	ModTime() time.Time // modification time
+	IsDir() bool        // abbreviation for Mode().IsDir()
+	Sys() interface{}   // underlying data source (can return nil)
+}
+
+type FileMode uint32
+
+// Mode constants, copied from the mainline Go source
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
+const (
+	// The single letters are the abbreviations used by the String method's formatting.
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // T: temporary file; Plan 9 only
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
+	ModeSticky                                     // t: sticky
+	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
+
+	ModePerm FileMode = 0777 // Unix permission bits
+)
+
+// IsDir is a stub, always returning false
+func (m FileMode) IsDir() bool {
+	return false
+}

src/os/file_other.go

@@ -1,4 +1,4 @@
-// +build baremetal wasm
+// +build baremetal wasm,!wasi
 
 package os
 

src/os/file_unix.go

@@ -1,8 +1,9 @@
-// +build darwin linux,!baremetal,!wasi freebsd,!baremetal
+// +build darwin linux,!baremetal freebsd,!baremetal
 
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -77,6 +78,9 @@ type unixFileHandle uintptr
 func (f unixFileHandle) Read(b []byte) (n int, err error) {
 	n, err = syscall.Read(int(f), b)
 	err = handleSyscallError(err)
+	if n == 0 && err == nil {
+		err = io.EOF
+	}
 	return
 }
 

src/runtime/runtime_wasm_wasi.go

@@ -8,11 +8,16 @@ import (
 
 type timeUnit int64
 
+// libc constructors
+//export __wasm_call_ctors
+func __wasm_call_ctors()
+
 //export _start
 func _start() {
 	// These need to be initialized early so that the heap can be initialized.
 	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
 	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
+	__wasm_call_ctors()
 	run()
 }
 

src/syscall/errno_other.go

@@ -0,0 +1,5 @@
+// +build !wasi,!darwin
+
+package syscall
+
+func (e Errno) Is(target error) bool { return false }

src/syscall/syscall_libc.go

@@ -13,12 +13,15 @@ type sliceHeader struct {
 }
 
 func Close(fd int) (err error) {
-	return ENOSYS // TODO
+	if libc_close(fd) < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Write(fd int, p []byte) (n int, err error) {
 	buf, count := splitSlice(p)
-	n = libc_write(int32(fd), buf, uint(count))
+	n = libc_write(fd, buf, uint(count))
 	if n < 0 {
 		err = getErrno()
 	}
@@ -26,15 +29,25 @@ func Write(fd int, p []byte) (n int, err error) {
 }
 
 func Read(fd int, p []byte) (n int, err error) {
-	return 0, ENOSYS // TODO
+	buf, count := splitSlice(p)
+	n = libc_read(fd, buf, uint(count))
+	if n < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Seek(fd int, offset int64, whence int) (off int64, err error) {
 	return 0, ENOSYS // TODO
 }
 
-func Open(path string, mode int, perm uint32) (fd int, err error) {
-	return 0, ENOSYS // TODO
+func Open(path string, flag int, mode uint32) (fd int, err error) {
+	data := append([]byte(path), 0)
+	fd = libc_open(&data[0], flag, mode)
+	if fd < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Mkdir(path string, mode uint32) (err error) {
@@ -78,8 +91,20 @@ func splitSlice(p []byte) (buf *byte, len uintptr) {
 
 // ssize_t write(int fd, const void *buf, size_t count)
 //export write
-func libc_write(fd int32, buf *byte, count uint) int
+func libc_write(fd int, buf *byte, count uint) int
 
 // char *getenv(const char *name);
 //export getenv
 func libc_getenv(name *byte) *byte
+
+// ssize_t read(int fd, void *buf, size_t count);
+//export read
+func libc_read(fd int, buf *byte, count uint) int
+
+// int open(const char *pathname, int flags, mode_t mode);
+//export open
+func libc_open(pathname *byte, flags int, mode uint32) int
+
+// int close(int fd)
+//export close
+func libc_close(fd int) int

src/syscall/syscall_libc_darwin.go

@@ -1,3 +1,5 @@
+// +build darwin
+
 package syscall
 
 // This file defines errno and constants to match the darwin libsystem ABI.
@@ -22,10 +24,25 @@ func getErrno() Errno {
 	return Errno(uintptr(*errptr))
 }
 
+func (e Errno) Is(target error) bool {
+	switch target.Error() {
+	case "permission denied":
+		return e == EACCES || e == EPERM
+	case "file already exists":
+		return e == EEXIST
+	case "file does not exist":
+		return e == ENOENT
+	}
+	return false
+}
+
 const (
+	EPERM       Errno = 0x1
 	ENOENT      Errno = 0x2
+	EACCES      Errno = 0xd
 	EEXIST      Errno = 0x11
 	EINTR       Errno = 0x4
+	ENOTDIR     Errno = 0x14
 	EMFILE      Errno = 0x18
 	EAGAIN      Errno = 0x23
 	ETIMEDOUT   Errno = 0x3c

src/syscall/syscall_libc_nintendoswitch.go

@@ -2,8 +2,6 @@
 
 package syscall
 
-import "errors"
-
 // A Signal is a number describing a process signal.
 // It implements the os.Signal interface.
 type Signal int
@@ -32,7 +30,6 @@ const (
 	O_RDWR   = 2
 
 	O_CREAT  = 0100
-	O_CREATE = O_CREAT
 	O_TRUNC  = 01000
 	O_APPEND = 02000
 	O_EXCL   = 0200
@@ -41,8 +38,9 @@ const (
 	O_CLOEXEC = 0
 )
 
-var dummyError = errors.New("unknown syscall error")
+//go:extern errno
+var libcErrno uintptr
 
 func getErrno() error {
-	return dummyError
+	return Errno(libcErrno)
 }

src/syscall/syscall_libc_wasi.go

@@ -33,7 +33,6 @@ const (
 	O_RDWR   = O_RDONLY | O_WRONLY
 
 	O_CREAT  = __WASI_OFLAGS_CREAT << 12
-	O_CREATE = O_CREAT
 	O_TRUNC  = __WASI_OFLAGS_TRUNC << 12
 	O_APPEND = __WASI_FDFLAGS_APPEND
 	O_EXCL   = __WASI_OFLAGS_EXCL << 12
@@ -48,3 +47,95 @@ var libcErrno uintptr
 func getErrno() error {
 	return Errno(libcErrno)
 }
+
+func (e Errno) Is(target error) bool {
+	switch target.Error() {
+	case "permission denied":
+		return e == EACCES || e == EPERM || e == ENOTCAPABLE // ENOTCAPABLE is unique in WASI
+	case "file already exists":
+		return e == EEXIST || e == ENOTEMPTY
+	case "file does not exist":
+		return e == ENOENT
+	}
+	return false
+}
+
+// https://github.com/WebAssembly/wasi-libc/blob/main/libc-bottom-half/headers/public/__errno.h
+const (
+	E2BIG           Errno = 1      /* Argument list too long */
+	EACCES          Errno = 2      /* Permission denied */
+	EADDRINUSE      Errno = 3      /* Address already in use */
+	EADDRNOTAVAIL   Errno = 4      /* Address not available */
+	EAFNOSUPPORT    Errno = 5      /* Address family not supported by protocol family */
+	EAGAIN          Errno = 6      /* Try again */
+	EWOULDBLOCK     Errno = EAGAIN /* Operation would block */
+	EALREADY        Errno = 7      /* Socket already connected */
+	EBADF           Errno = 8      /* Bad file number */
+	EBADMSG         Errno = 9      /* Trying to read unreadable message */
+	EBUSY           Errno = 10     /* Device or resource busy */
+	ECANCELED       Errno = 11     /* Operation canceled. */
+	ECHILD          Errno = 12     /* No child processes */
+	ECONNABORTED    Errno = 13     /* Connection aborted */
+	ECONNREFUSED    Errno = 14     /* Connection refused */
+	ECONNRESET      Errno = 15     /* Connection reset by peer */
+	EDEADLK         Errno = 16     /* Deadlock condition */
+	EDESTADDRREQ    Errno = 17     /* Destination address required */
+	EDOM            Errno = 18     /* Math arg out of domain of func */
+	EDQUOT          Errno = 19     /* Quota exceeded */
+	EEXIST          Errno = 20     /* File exists */
+	EFAULT          Errno = 21     /* Bad address */
+	EFBIG           Errno = 22     /* File too large */
+	EHOSTUNREACH    Errno = 23     /* Host is unreachable */
+	EIDRM           Errno = 24     /* Identifier removed */
+	EILSEQ          Errno = 25
+	EINPROGRESS     Errno = 26 /* Connection already in progress */
+	EINTR           Errno = 27 /* Interrupted system call */
+	EINVAL          Errno = 28 /* Invalid argument */
+	EIO             Errno = 29 /* I/O error */
+	EISCONN         Errno = 30 /* Socket is already connected */
+	EISDIR          Errno = 31 /* Is a directory */
+	ELOOP           Errno = 32 /* Too many symbolic links */
+	EMFILE          Errno = 33 /* Too many open files */
+	EMLINK          Errno = 34 /* Too many links */
+	EMSGSIZE        Errno = 35 /* Message too long */
+	EMULTIHOP       Errno = 36 /* Multihop attempted */
+	ENAMETOOLONG    Errno = 37 /* File name too long */
+	ENETDOWN        Errno = 38 /* Network interface is not configured */
+	ENETRESET       Errno = 39
+	ENETUNREACH     Errno = 40         /* Network is unreachable */
+	ENFILE          Errno = 41         /* File table overflow */
+	ENOBUFS         Errno = 42         /* No buffer space available */
+	ENODEV          Errno = 43         /* No such device */
+	ENOENT          Errno = 44         /* No such file or directory */
+	ENOEXEC         Errno = 45         /* Exec format error */
+	ENOLCK          Errno = 46         /* No record locks available */
+	ENOLINK         Errno = 47         /* The link has been severed */
+	ENOMEM          Errno = 48         /* Out of memory */
+	ENOMSG          Errno = 49         /* No message of desired type */
+	ENOPROTOOPT     Errno = 50         /* Protocol not available */
+	ENOSPC          Errno = 51         /* No space left on device */
+	ENOSYS          Errno = 52         /* Function not implemented */
+	ENOTCONN        Errno = 53         /* Socket is not connected */
+	ENOTDIR         Errno = 54         /* Not a directory */
+	ENOTEMPTY       Errno = 55         /* Directory not empty */
+	ENOTSOCK        Errno = 57         /* Socket operation on non-socket */
+	ESOCKTNOSUPPORT Errno = 58         /* Socket type not supported */
+	EOPNOTSUPP      Errno = 58         /* Operation not supported on transport endpoint */
+	ENOTSUP         Errno = EOPNOTSUPP /* Not supported */
+	ENOTTY          Errno = 59         /* Not a typewriter */
+	ENXIO           Errno = 60         /* No such device or address */
+	EOVERFLOW       Errno = 61         /* Value too large for defined data type */
+	EPERM           Errno = 63         /* Operation not permitted */
+	EPIPE           Errno = 64         /* Broken pipe */
+	EPROTO          Errno = 65         /* Protocol error */
+	EPROTONOSUPPORT Errno = 66         /* Unknown protocol */
+	EPROTOTYPE      Errno = 67         /* Protocol wrong type for socket */
+	ERANGE          Errno = 68         /* Math result not representable */
+	EROFS           Errno = 69         /* Read-only file system */
+	ESPIPE          Errno = 70         /* Illegal seek */
+	ESRCH           Errno = 71         /* No such process */
+	ESTALE          Errno = 72
+	ETIMEDOUT       Errno = 73 /* Connection timed out */
+	EXDEV           Errno = 75 /* Cross-device link */
+	ENOTCAPABLE     Errno = 76 /* Extension: Capabilities insufficient. */
+)

src/syscall/tables_baremetal.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build baremetal nintendoswitch wasi
+// +build baremetal nintendoswitch
 
 package syscall
 

testdata/libc/filesystem.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	_, err := os.Open("non-exist")
+	if !os.IsNotExist(err) {
+		panic("should be non exist error")
+	}
+
+	f, err := os.Open("testdata/libc/filesystem.txt")
+	if err != nil {
+		panic(err)
+	}
+
+	defer func() {
+		if err := f.Close(); err != nil {
+			panic(err)
+		}
+
+		// read after close: error should be returned
+		_, err := f.Read(make([]byte, 10))
+		if err == nil {
+			panic("error expected for reading after closing files")
+		}
+	}()
+
+	data, err := ioutil.ReadAll(f)
+	if err != nil {
+		panic(err)
+	}
+
+	print(string(data))
+
+}

testdata/libc/filesystem.txt

@@ -0,0 +1,6 @@
+abcdefg
+1
+2
+3
+4
+5