dir_unix.go

Documentation: os

     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) || linux || netbsd || openbsd || solaris
     6  
     7  package os
     8  
     9  import (
    10  	"io"
    11  	"runtime"
    12  	"sync"
    13  	"syscall"
    14  	"unsafe"
    15  )
    16  
    17  // Auxiliary information if the File describes a directory
    18  type dirInfo struct {
    19  	buf  *[]byte // buffer for directory I/O
    20  	nbuf int     // length of buf; return value from Getdirentries
    21  	bufp int     // location of next record in buf.
    22  }
    23  
    24  const (
    25  	// More than 5760 to work around https://golang.org/issue/24015.
    26  	blockSize = 8192
    27  )
    28  
    29  var dirBufPool = sync.Pool{
    30  	New: func() any {
    31  		// The buffer must be at least a block long.
    32  		buf := make([]byte, blockSize)
    33  		return &buf
    34  	},
    35  }
    36  
    37  func (d *dirInfo) close() {
    38  	if d.buf != nil {
    39  		dirBufPool.Put(d.buf)
    40  		d.buf = nil
    41  	}
    42  }
    43  
    44  func (f *File) readdir(n int, mode readdirMode) (names []string, dirents []DirEntry, infos []FileInfo, err error) {
    45  	// If this file has no dirinfo, create one.
    46  	if f.dirinfo == nil {
    47  		f.dirinfo = new(dirInfo)
    48  		f.dirinfo.buf = dirBufPool.Get().(*[]byte)
    49  	}
    50  	d := f.dirinfo
    51  
    52  	// Change the meaning of n for the implementation below.
    53  	//
    54  	// The n above was for the public interface of "if n <= 0,
    55  	// Readdir returns all the FileInfo from the directory in a
    56  	// single slice".
    57  	//
    58  	// But below, we use only negative to mean looping until the
    59  	// end and positive to mean bounded, with positive
    60  	// terminating at 0.
    61  	if n == 0 {
    62  		n = -1
    63  	}
    64  
    65  	for n != 0 {
    66  		// Refill the buffer if necessary
    67  		if d.bufp >= d.nbuf {
    68  			d.bufp = 0
    69  			var errno error
    70  			d.nbuf, errno = f.pfd.ReadDirent(*d.buf)
    71  			runtime.KeepAlive(f)
    72  			if errno != nil {
    73  				return names, dirents, infos, &PathError{Op: "readdirent", Path: f.name, Err: errno}
    74  			}
    75  			if d.nbuf <= 0 {
    76  				break // EOF
    77  			}
    78  		}
    79  
    80  		// Drain the buffer
    81  		buf := (*d.buf)[d.bufp:d.nbuf]
    82  		reclen, ok := direntReclen(buf)
    83  		if !ok || reclen > uint64(len(buf)) {
    84  			break
    85  		}
    86  		rec := buf[:reclen]
    87  		d.bufp += int(reclen)
    88  		ino, ok := direntIno(rec)
    89  		if !ok {
    90  			break
    91  		}
    92  		if ino == 0 {
    93  			continue
    94  		}
    95  		const namoff = uint64(unsafe.Offsetof(syscall.Dirent{}.Name))
    96  		namlen, ok := direntNamlen(rec)
    97  		if !ok || namoff+namlen > uint64(len(rec)) {
    98  			break
    99  		}
   100  		name := rec[namoff : namoff+namlen]
   101  		for i, c := range name {
   102  			if c == 0 {
   103  				name = name[:i]
   104  				break
   105  			}
   106  		}
   107  		// Check for useless names before allocating a string.
   108  		if string(name) == "." || string(name) == ".." {
   109  			continue
   110  		}
   111  		if n > 0 { // see 'n == 0' comment above
   112  			n--
   113  		}
   114  		if mode == readdirName {
   115  			names = append(names, string(name))
   116  		} else if mode == readdirDirEntry {
   117  			de, err := newUnixDirent(f.name, string(name), direntType(rec))
   118  			if IsNotExist(err) {
   119  				// File disappeared between readdir and stat.
   120  				// Treat as if it didn't exist.
   121  				continue
   122  			}
   123  			if err != nil {
   124  				return nil, dirents, nil, err
   125  			}
   126  			dirents = append(dirents, de)
   127  		} else {
   128  			info, err := lstat(f.name + "/" + string(name))
   129  			if IsNotExist(err) {
   130  				// File disappeared between readdir + stat.
   131  				// Treat as if it didn't exist.
   132  				continue
   133  			}
   134  			if err != nil {
   135  				return nil, nil, infos, err
   136  			}
   137  			infos = append(infos, info)
   138  		}
   139  	}
   140  
   141  	if n > 0 && len(names)+len(dirents)+len(infos) == 0 {
   142  		return nil, nil, nil, io.EOF
   143  	}
   144  	return names, dirents, infos, nil
   145  }
   146  
   147  // readInt returns the size-bytes unsigned integer in native byte order at offset off.
   148  func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {
   149  	if len(b) < int(off+size) {
   150  		return 0, false
   151  	}
   152  	if isBigEndian {
   153  		return readIntBE(b[off:], size), true
   154  	}
   155  	return readIntLE(b[off:], size), true
   156  }
   157  
   158  func readIntBE(b []byte, size uintptr) uint64 {
   159  	switch size {
   160  	case 1:
   161  		return uint64(b[0])
   162  	case 2:
   163  		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
   164  		return uint64(b[1]) | uint64(b[0])<<8
   165  	case 4:
   166  		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
   167  		return uint64(b[3]) | uint64(b[2])<<8 | uint64(b[1])<<16 | uint64(b[0])<<24
   168  	case 8:
   169  		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   170  		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
   171  			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
   172  	default:
   173  		panic("syscall: readInt with unsupported size")
   174  	}
   175  }
   176  
   177  func readIntLE(b []byte, size uintptr) uint64 {
   178  	switch size {
   179  	case 1:
   180  		return uint64(b[0])
   181  	case 2:
   182  		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
   183  		return uint64(b[0]) | uint64(b[1])<<8
   184  	case 4:
   185  		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
   186  		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24
   187  	case 8:
   188  		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   189  		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
   190  			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
   191  	default:
   192  		panic("syscall: readInt with unsupported size")
   193  	}
   194  }
   195
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