os: implement readdir for linux

Author: dkegel-fastly

src/os/dir_other.go

@@ -1,4 +1,4 @@
-// +build baremetal wasm,!wasi
+// +build baremetal wasi
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -10,6 +10,9 @@ import (
 	"syscall"
 )
 
+type dirInfo struct {
+}
+
 func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
 	return nil, nil, nil, &PathError{Op: "readdir unimplemented", Err: syscall.ENOTDIR}
 }

src/os/dir_unix.go

@@ -1,4 +1,4 @@
-// +build linux,!baremetal
+// +build linux,!baremetal,!wasi
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -7,14 +7,189 @@
 package os
 
 import (
+	"io"
+	"sync"
 	"syscall"
+	"unsafe"
 )
 
 // Auxiliary information if the File describes a directory
 type dirInfo struct {
-	// TODO
+	buf  *[]byte // buffer for directory I/O
+	nbuf int     // length of buf; return value from Getdirentries
+	bufp int     // location of next record in buf.
+}
+
+const (
+	// More than 5760 to work around https://golang.org/issue/24015.
+	blockSize = 8192
+)
+
+var dirBufPool = sync.Pool{
+	New: func() interface{} {
+		// The buffer must be at least a block long.
+		buf := make([]byte, blockSize)
+		return &buf
+	},
+}
+
+func (d *dirInfo) close() {
+	if d.buf != nil {
+		dirBufPool.Put(d.buf)
+		d.buf = nil
+	}
 }
 
 func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
-	return nil, nil, nil, &PathError{Op: "readdir unimplemented", Err: syscall.ENOTDIR}
+	// If this file has no dirinfo, create one.
+	if f.dirinfo == nil {
+		f.dirinfo = new(dirInfo)
+		f.dirinfo.buf = dirBufPool.Get().(*[]byte)
+	}
+	d := f.dirinfo
+
+	// Change the meaning of n for the implementation below.
+	//
+	// The n above was for the public interface of "if n <= 0,
+	// Readdir returns all the FileInfo from the directory in a
+	// single slice".
+	//
+	// But below, we use only negative to mean looping until the
+	// end and positive to mean bounded, with positive
+	// terminating at 0.
+	if n == 0 {
+		n = -1
+	}
+
+	for n != 0 {
+		// Refill the buffer if necessary
+		if d.bufp >= d.nbuf {
+			d.bufp = 0
+			var errno error
+			d.nbuf, errno = syscall.ReadDirent(syscallFd(f.handle.(unixFileHandle)), *d.buf)
+			if d.nbuf < 0 {
+				errno = handleSyscallError(errno)
+			}
+			if errno != nil {
+				return names, dirents, infos, &PathError{Op: "readdirent", Path: f.name, Err: errno}
+			}
+			if d.nbuf <= 0 {
+				break // EOF
+			}
+		}
+
+		// Drain the buffer
+		buf := (*d.buf)[d.bufp:d.nbuf]
+		reclen, ok := direntReclen(buf)
+		if !ok || reclen > uint64(len(buf)) {
+			break
+		}
+		rec := buf[:reclen]
+		d.bufp += int(reclen)
+		ino, ok := direntIno(rec)
+		if !ok {
+			break
+		}
+		if ino == 0 {
+			continue
+		}
+		const namoff = uint64(unsafe.Offsetof(syscall.Dirent{}.Name))
+		namlen, ok := direntNamlen(rec)
+		if !ok || namoff+namlen > uint64(len(rec)) {
+			break
+		}
+		name := rec[namoff : namoff+namlen]
+		for i, c := range name {
+			if c == 0 {
+				name = name[:i]
+				break
+			}
+		}
+		// Check for useless names before allocating a string.
+		if string(name) == "." || string(name) == ".." {
+			continue
+		}
+		if n > 0 { // see 'n == 0' comment above
+			n--
+		}
+		if mode == readdirName {
+			names = append(names, string(name))
+		} else if mode == readdirDirEntry {
+			de, err := newUnixDirent(f.name, string(name), direntType(rec))
+			if IsNotExist(err) {
+				// File disappeared between readdir and stat.
+				// Treat as if it didn't exist.
+				continue
+			}
+			if err != nil {
+				return nil, dirents, nil, err
+			}
+			dirents = append(dirents, de)
+		} else {
+			info, err := lstat(f.name + "/" + string(name))
+			if IsNotExist(err) {
+				// File disappeared between readdir + stat.
+				// Treat as if it didn't exist.
+				continue
+			}
+			if err != nil {
+				return nil, nil, infos, err
+			}
+			infos = append(infos, info)
+		}
+	}
+
+	if n > 0 && len(names)+len(dirents)+len(infos) == 0 {
+		return nil, nil, nil, io.EOF
+	}
+	return names, dirents, infos, nil
+}
+
+// readInt returns the size-bytes unsigned integer in native byte order at offset off.
+func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {
+	if len(b) < int(off+size) {
+		return 0, false
+	}
+	if isBigEndian {
+		return readIntBE(b[off:], size), true
+	}
+	return readIntLE(b[off:], size), true
+}
+
+func readIntBE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[1]) | uint64(b[0])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[3]) | uint64(b[2])<<8 | uint64(b[1])<<16 | uint64(b[0])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
+			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
+}
+
+func readIntLE(b []byte, size uintptr) uint64 {
+	switch size {
+	case 1:
+		return uint64(b[0])
+	case 2:
+		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8
+	case 4:
+		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24
+	case 8:
+		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
+		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+	default:
+		panic("syscall: readInt with unsupported size")
+	}
 }

src/os/dirent_linux.go

@@ -0,0 +1,53 @@
+// +build !baremetal,!js,!wasi
+
+// Copyright 2020 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 os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func direntIno(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(syscall.Dirent{}.Ino), unsafe.Sizeof(syscall.Dirent{}.Ino))
+}
+
+func direntReclen(buf []byte) (uint64, bool) {
+	return readInt(buf, unsafe.Offsetof(syscall.Dirent{}.Reclen), unsafe.Sizeof(syscall.Dirent{}.Reclen))
+}
+
+func direntNamlen(buf []byte) (uint64, bool) {
+	reclen, ok := direntReclen(buf)
+	if !ok {
+		return 0, false
+	}
+	return reclen - uint64(unsafe.Offsetof(syscall.Dirent{}.Name)), true
+}
+
+func direntType(buf []byte) FileMode {
+	off := unsafe.Offsetof(syscall.Dirent{}.Type)
+	if off >= uintptr(len(buf)) {
+		return ^FileMode(0) // unknown
+	}
+	typ := buf[off]
+	switch typ {
+	case syscall.DT_BLK:
+		return ModeDevice
+	case syscall.DT_CHR:
+		return ModeDevice | ModeCharDevice
+	case syscall.DT_DIR:
+		return ModeDir
+	case syscall.DT_FIFO:
+		return ModeNamedPipe
+	case syscall.DT_LNK:
+		return ModeSymlink
+	case syscall.DT_REG:
+		return 0
+	case syscall.DT_SOCK:
+		return ModeSocket
+	}
+	return ^FileMode(0) // unknown
+}

src/os/endian_big.go

@@ -0,0 +1,9 @@
+// Copyright 2016 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.
+//
+// +build ppc64 mips mips64
+
+package os
+
+const isBigEndian = true

src/os/endian_little.go

@@ -0,0 +1,9 @@
+// Copyright 2016 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.
+//
+// +build 386 amd64 arm arm64 ppc64le mips64le mipsle riscv64 wasm
+
+package os
+
+const isBigEndian = false