dir_unix.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build aix || dragonfly || freebsd || (js && wasm) || wasip1 || linux || netbsd || openbsd || solaris
     6  
     7  package os
     8  
     9  import (
    10  	"internal/byteorder"
    11  	"internal/goarch"
    12  	"io"
    13  	"runtime"
    14  	"sync"
    15  	"syscall"
    16  	"unsafe"
    17  )
    18  
    19  // Auxiliary information if the File describes a directory
    20  type dirInfo struct {
    21  	mu   sync.Mutex
    22  	buf  *[]byte // buffer for directory I/O
    23  	nbuf int     // length of buf; return value from Getdirentries
    24  	bufp int     // location of next record in buf.
    25  }
    26  
    27  const (
    28  	// More than 5760 to work around https://golang.org/issue/24015.
    29  	blockSize = 8192
    30  )
    31  
    32  var dirBufPool = sync.Pool{
    33  	New: func() any {
    34  		// The buffer must be at least a block long.
    35  		buf := make([]byte, blockSize)
    36  		return &buf
    37  	},
    38  }
    39  
    40  func (d *dirInfo) close() {
    41  	if d.buf != nil {
    42  		dirBufPool.Put(d.buf)
    43  		d.buf = nil
    44  	}
    45  }
    46  
    47  func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
    48  	// If this file has no dirInfo, create one.
    49  	d := f.dirinfo.Load()
    50  	if d == nil {
    51  		d = new(dirInfo)
    52  		f.dirinfo.Store(d)
    53  	}
    54  	d.mu.Lock()
    55  	defer d.mu.Unlock()
    56  	if d.buf == nil {
    57  		d.buf = dirBufPool.Get().(*[]byte)
    58  	}
    59  
    60  	// Change the meaning of n for the implementation below.
    61  	//
    62  	// The n above was for the public interface of "if n <= 0,
    63  	// Readdir returns all the FileInfo from the directory in a
    64  	// single slice".
    65  	//
    66  	// But below, we use only negative to mean looping until the
    67  	// end and positive to mean bounded, with positive
    68  	// terminating at 0.
    69  	if n == 0 {
    70  		n = -1
    71  	}
    72  
    73  	for n != 0 {
    74  		// Refill the buffer if necessary
    75  		if d.bufp >= d.nbuf {
    76  			d.bufp = 0
    77  			var errno error
    78  			d.nbuf, errno = f.pfd.ReadDirent(*d.buf)
    79  			runtime.KeepAlive(f)
    80  			if errno != nil {
    81  				return names, dirents, infos, &PathError{Op: "readdirent", Path: f.name, Err: errno}
    82  			}
    83  			if d.nbuf <= 0 {
    84  				// Optimization: we can return the buffer to the pool, there is nothing else to read.
    85  				dirBufPool.Put(d.buf)
    86  				d.buf = nil
    87  				break // EOF
    88  			}
    89  		}
    90  
    91  		// Drain the buffer
    92  		buf := (*d.buf)[d.bufp:d.nbuf]
    93  		reclen, ok := direntReclen(buf)
    94  		if !ok || reclen > uint64(len(buf)) {
    95  			break
    96  		}
    97  		rec := buf[:reclen]
    98  		d.bufp += int(reclen)
    99  		ino, ok := direntIno(rec)
   100  		if !ok {
   101  			break
   102  		}
   103  		// When building to wasip1, the host runtime might be running on Windows
   104  		// or might expose a remote file system which does not have the concept
   105  		// of inodes. Therefore, we cannot make the assumption that it is safe
   106  		// to skip entries with zero inodes.
   107  		if ino == 0 && runtime.GOOS != "wasip1" {
   108  			continue
   109  		}
   110  		const namoff = uint64(unsafe.Offsetof(syscall.Dirent{}.Name))
   111  		namlen, ok := direntNamlen(rec)
   112  		if !ok || namoff+namlen > uint64(len(rec)) {
   113  			break
   114  		}
   115  		name := rec[namoff : namoff+namlen]
   116  		for i, c := range name {
   117  			if c == 0 {
   118  				name = name[:i]
   119  				break
   120  			}
   121  		}
   122  		// Check for useless names before allocating a string.
   123  		if string(name) == "." || string(name) == ".." {
   124  			continue
   125  		}
   126  		if n > 0 { // see 'n == 0' comment above
   127  			n--
   128  		}
   129  		if mode == readdirName {
   130  			names = append(names, string(name))
   131  		} else if mode == readdirDirEntry {
   132  			de, err := newUnixDirent(f.name, string(name), direntType(rec))
   133  			if IsNotExist(err) {
   134  				// File disappeared between readdir and stat.
   135  				// Treat as if it didn't exist.
   136  				continue
   137  			}
   138  			if err != nil {
   139  				return nil, dirents, nil, err
   140  			}
   141  			dirents = append(dirents, de)
   142  		} else {
   143  			info, err := lstat(f.name + "/" + string(name))
   144  			if IsNotExist(err) {
   145  				// File disappeared between readdir + stat.
   146  				// Treat as if it didn't exist.
   147  				continue
   148  			}
   149  			if err != nil {
   150  				return nil, nil, infos, err
   151  			}
   152  			infos = append(infos, info)
   153  		}
   154  	}
   155  
   156  	if n > 0 && len(names)+len(dirents)+len(infos) == 0 {
   157  		return nil, nil, nil, io.EOF
   158  	}
   159  	return names, dirents, infos, nil
   160  }
   161  
   162  // readInt returns the size-bytes unsigned integer in native byte order at offset off.
   163  func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {
   164  	if len(b) < int(off+size) {
   165  		return 0, false
   166  	}
   167  	if goarch.BigEndian {
   168  		return readIntBE(b[off:], size), true
   169  	}
   170  	return readIntLE(b[off:], size), true
   171  }
   172  
   173  func readIntBE(b []byte, size uintptr) uint64 {
   174  	switch size {
   175  	case 1:
   176  		return uint64(b[0])
   177  	case 2:
   178  		return uint64(byteorder.BeUint16(b))
   179  	case 4:
   180  		return uint64(byteorder.BeUint32(b))
   181  	case 8:
   182  		return uint64(byteorder.BeUint64(b))
   183  	default:
   184  		panic("syscall: readInt with unsupported size")
   185  	}
   186  }
   187  
   188  func readIntLE(b []byte, size uintptr) uint64 {
   189  	switch size {
   190  	case 1:
   191  		return uint64(b[0])
   192  	case 2:
   193  		return uint64(byteorder.LeUint16(b))
   194  	case 4:
   195  		return uint64(byteorder.LeUint32(b))
   196  	case 8:
   197  		return uint64(byteorder.LeUint64(b))
   198  	default:
   199  		panic("syscall: readInt with unsupported size")
   200  	}
   201  }
   202
View as plain text