1use crate::fd::{AsFd, BorrowedFd, OwnedFd};
2use crate::ffi::{CStr, CString};
3use crate::fs::{
4 fcntl_getfl, fstat, fstatfs, fstatvfs, openat, FileType, Mode, OFlags, Stat, StatFs, StatVfs,
5};
6use crate::io;
7#[cfg(feature = "process")]
8use crate::process::fchdir;
9use crate::utils::as_ptr;
10use alloc::borrow::ToOwned as _;
11use alloc::vec::Vec;
12use core::fmt;
13use core::mem::size_of;
14use linux_raw_sys::general::{linux_dirent64, SEEK_SET};
15
16/// `DIR*`
17pub struct Dir {
18 /// The `OwnedFd` that we read directory entries from.
19 fd: OwnedFd,
20
21 /// Have we seen any errors in this iteration?
22 any_errors: bool,
23
24 /// Should we rewind the stream on the next iteration?
25 rewind: bool,
26
27 /// The buffer for `linux_dirent64` entries.
28 buf: Vec<u8>,
29
30 /// Where we are in the buffer.
31 pos: usize,
32}
33
34impl Dir {
35 /// Take ownership of `fd` and construct a `Dir` that reads entries from
36 /// the given directory file descriptor.
37 #[inline]
38 pub fn new<Fd: Into<OwnedFd>>(fd: Fd) -> io::Result<Self> {
39 Self::_new(fd.into())
40 }
41
42 #[inline]
43 fn _new(fd: OwnedFd) -> io::Result<Self> {
44 Ok(Self {
45 fd,
46 any_errors: false,
47 rewind: false,
48 buf: Vec::new(),
49 pos: 0,
50 })
51 }
52
53 /// Borrow `fd` and construct a `Dir` that reads entries from the given
54 /// directory file descriptor.
55 #[inline]
56 pub fn read_from<Fd: AsFd>(fd: Fd) -> io::Result<Self> {
57 Self::_read_from(fd.as_fd())
58 }
59
60 #[inline]
61 fn _read_from(fd: BorrowedFd<'_>) -> io::Result<Self> {
62 let flags = fcntl_getfl(fd)?;
63 let fd_for_dir = openat(fd, cstr!("."), flags | OFlags::CLOEXEC, Mode::empty())?;
64
65 Ok(Self {
66 fd: fd_for_dir,
67 any_errors: false,
68 rewind: false,
69 buf: Vec::new(),
70 pos: 0,
71 })
72 }
73
74 /// `rewinddir(self)`
75 #[inline]
76 pub fn rewind(&mut self) {
77 self.any_errors = false;
78 self.rewind = true;
79 self.pos = self.buf.len();
80 }
81
82 /// `seekdir(self, offset)`
83 ///
84 /// This function is only available on 64-bit platforms because it's
85 /// implemented using [`libc::seekdir`] which only supports offsets that
86 /// fit in a `c_long`.
87 ///
88 /// [`libc::seekdir`]: https://docs.rs/libc/*/arm-unknown-linux-gnueabihf/libc/fn.seekdir.html
89 // In the linux_raw backend here, we don't use `libc::seekdir` and don't
90 // have this limitation, but it's a goal of rustix to support the same API
91 // on both the linux_raw and libc backends.
92 #[cfg(target_pointer_width = "64")]
93 #[cfg_attr(docsrs, doc(cfg(target_pointer_width = "64")))]
94 #[doc(alias = "seekdir")]
95 #[inline]
96 pub fn seek(&mut self, offset: i64) -> io::Result<()> {
97 self.any_errors = false;
98 self.rewind = false;
99 self.pos = self.buf.len();
100 match io::retry_on_intr(|| {
101 crate::backend::fs::syscalls::_seek(self.fd.as_fd(), offset, SEEK_SET)
102 }) {
103 Ok(_) => Ok(()),
104 Err(err) => {
105 self.any_errors = true;
106 Err(err)
107 }
108 }
109 }
110
111 /// `readdir(self)`, where `None` means the end of the directory.
112 pub fn read(&mut self) -> Option<io::Result<DirEntry>> {
113 // If we've seen errors, don't continue to try to read anything
114 // further.
115 if self.any_errors {
116 return None;
117 }
118
119 // If a rewind was requested, seek to the beginning.
120 if self.rewind {
121 self.rewind = false;
122 match io::retry_on_intr(|| {
123 crate::backend::fs::syscalls::_seek(self.fd.as_fd(), 0, SEEK_SET)
124 }) {
125 Ok(_) => (),
126 Err(err) => {
127 self.any_errors = true;
128 return Some(Err(err));
129 }
130 }
131 }
132
133 // Compute linux_dirent64 field offsets.
134 let z = linux_dirent64 {
135 d_ino: 0_u64,
136 d_off: 0_i64,
137 d_type: 0_u8,
138 d_reclen: 0_u16,
139 d_name: Default::default(),
140 };
141 let base = as_ptr(&z) as usize;
142 let offsetof_d_reclen = (as_ptr(&z.d_reclen) as usize) - base;
143 let offsetof_d_name = (as_ptr(&z.d_name) as usize) - base;
144 let offsetof_d_ino = (as_ptr(&z.d_ino) as usize) - base;
145 let offsetof_d_off = (as_ptr(&z.d_off) as usize) - base;
146 let offsetof_d_type = (as_ptr(&z.d_type) as usize) - base;
147
148 // Test if we need more entries, and if so, read more.
149 if self.buf.len() - self.pos < size_of::<linux_dirent64>() {
150 match self.read_more()? {
151 Ok(()) => (),
152 Err(err) => return Some(Err(err)),
153 }
154 }
155
156 // We successfully read an entry. Extract the fields.
157 let pos = self.pos;
158
159 // Do an unaligned u16 load.
160 let d_reclen = u16::from_ne_bytes([
161 self.buf[pos + offsetof_d_reclen],
162 self.buf[pos + offsetof_d_reclen + 1],
163 ]);
164 assert!(self.buf.len() - pos >= d_reclen as usize);
165 self.pos += d_reclen as usize;
166
167 // Read the NUL-terminated name from the `d_name` field. Without
168 // `unsafe`, we need to scan for the NUL twice: once to obtain a size
169 // for the slice, and then once within `CStr::from_bytes_with_nul`.
170 let name_start = pos + offsetof_d_name;
171 let name_len = self.buf[name_start..]
172 .iter()
173 .position(|x| *x == b'\0')
174 .unwrap();
175 let name = CStr::from_bytes_with_nul(&self.buf[name_start..][..=name_len]).unwrap();
176 let name = name.to_owned();
177 assert!(name.as_bytes().len() <= self.buf.len() - name_start);
178
179 // Do an unaligned `u64` load for `d_ino`.
180 let d_ino = u64::from_ne_bytes([
181 self.buf[pos + offsetof_d_ino],
182 self.buf[pos + offsetof_d_ino + 1],
183 self.buf[pos + offsetof_d_ino + 2],
184 self.buf[pos + offsetof_d_ino + 3],
185 self.buf[pos + offsetof_d_ino + 4],
186 self.buf[pos + offsetof_d_ino + 5],
187 self.buf[pos + offsetof_d_ino + 6],
188 self.buf[pos + offsetof_d_ino + 7],
189 ]);
190
191 // Do an unaligned `i64` load for `d_off`.
192 let d_off = i64::from_ne_bytes([
193 self.buf[pos + offsetof_d_off],
194 self.buf[pos + offsetof_d_off + 1],
195 self.buf[pos + offsetof_d_off + 2],
196 self.buf[pos + offsetof_d_off + 3],
197 self.buf[pos + offsetof_d_off + 4],
198 self.buf[pos + offsetof_d_off + 5],
199 self.buf[pos + offsetof_d_off + 6],
200 self.buf[pos + offsetof_d_off + 7],
201 ]);
202
203 let d_type = self.buf[pos + offsetof_d_type];
204
205 // Check that our types correspond to the `linux_dirent64` types.
206 let _ = linux_dirent64 {
207 d_ino,
208 d_off,
209 d_type,
210 d_reclen,
211 d_name: Default::default(),
212 };
213
214 Some(Ok(DirEntry {
215 d_ino,
216 d_off,
217 d_type,
218 name,
219 }))
220 }
221
222 #[must_use]
223 fn read_more(&mut self) -> Option<io::Result<()>> {
224 // The first few times we're called, we allocate a relatively small
225 // buffer, because many directories are small. If we're called more,
226 // use progressively larger allocations, up to a fixed maximum.
227 //
228 // The specific sizes and policy here have not been tuned in detail yet
229 // and may need to be adjusted. In doing so, we should be careful to
230 // avoid unbounded buffer growth. This buffer only exists to share the
231 // cost of a `getdents` call over many entries, so if it gets too big,
232 // cache and heap usage will outweigh the benefit. And ultimately,
233 // directories can contain more entries than we can allocate contiguous
234 // memory for, so we'll always need to cap the size at some point.
235 if self.buf.len() < 1024 * size_of::<linux_dirent64>() {
236 self.buf.reserve(32 * size_of::<linux_dirent64>());
237 }
238 self.buf.resize(self.buf.capacity(), 0);
239 let nread = match io::retry_on_intr(|| {
240 crate::backend::fs::syscalls::getdents(self.fd.as_fd(), &mut self.buf)
241 }) {
242 Ok(nread) => nread,
243 Err(io::Errno::NOENT) => {
244 self.any_errors = true;
245 return None;
246 }
247 Err(err) => {
248 self.any_errors = true;
249 return Some(Err(err));
250 }
251 };
252 self.buf.resize(nread, 0);
253 self.pos = 0;
254 if nread == 0 {
255 None
256 } else {
257 Some(Ok(()))
258 }
259 }
260
261 /// `fstat(self)`
262 #[inline]
263 pub fn stat(&self) -> io::Result<Stat> {
264 fstat(&self.fd)
265 }
266
267 /// `fstatfs(self)`
268 #[inline]
269 pub fn statfs(&self) -> io::Result<StatFs> {
270 fstatfs(&self.fd)
271 }
272
273 /// `fstatvfs(self)`
274 #[inline]
275 pub fn statvfs(&self) -> io::Result<StatVfs> {
276 fstatvfs(&self.fd)
277 }
278
279 /// `fchdir(self)`
280 #[cfg(feature = "process")]
281 #[cfg_attr(docsrs, doc(cfg(feature = "process")))]
282 #[inline]
283 pub fn chdir(&self) -> io::Result<()> {
284 fchdir(&self.fd)
285 }
286}
287
288impl Iterator for Dir {
289 type Item = io::Result<DirEntry>;
290
291 #[inline]
292 fn next(&mut self) -> Option<Self::Item> {
293 Self::read(self)
294 }
295}
296
297impl fmt::Debug for Dir {
298 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
299 f.debug_struct("Dir").field(name:"fd", &self.fd).finish()
300 }
301}
302
303/// `struct dirent`
304#[derive(Debug)]
305pub struct DirEntry {
306 d_ino: u64,
307 d_type: u8,
308 d_off: i64,
309 name: CString,
310}
311
312impl DirEntry {
313 /// Returns the file name of this directory entry.
314 #[inline]
315 pub fn file_name(&self) -> &CStr {
316 &self.name
317 }
318
319 /// Returns the “offset” of this directory entry. This is not a true
320 /// numerical offset but an opaque cookie that identifies a position in the
321 /// given stream.
322 #[inline]
323 pub fn offset(&self) -> i64 {
324 self.d_off
325 }
326
327 /// Returns the type of this directory entry.
328 #[inline]
329 pub fn file_type(&self) -> FileType {
330 FileType::from_dirent_d_type(self.d_type)
331 }
332
333 /// Return the inode number of this directory entry.
334 #[inline]
335 pub fn ino(&self) -> u64 {
336 self.d_ino
337 }
338}
339
340#[cfg(test)]
341mod tests {
342 use super::*;
343
344 #[test]
345 fn dir_iterator_handles_io_errors() {
346 // create a dir, keep the FD, then delete the dir
347 let tmp = tempfile::tempdir().unwrap();
348 let fd = crate::fs::openat(
349 crate::fs::CWD,
350 tmp.path(),
351 crate::fs::OFlags::RDONLY | crate::fs::OFlags::CLOEXEC,
352 crate::fs::Mode::empty(),
353 )
354 .unwrap();
355
356 let file_fd = crate::fs::openat(
357 &fd,
358 tmp.path().join("test.txt"),
359 crate::fs::OFlags::WRONLY | crate::fs::OFlags::CREATE,
360 crate::fs::Mode::RWXU,
361 )
362 .unwrap();
363
364 let mut dir = Dir::read_from(&fd).unwrap();
365
366 // Reach inside the `Dir` and replace its directory with a file, which
367 // will cause the subsequent `getdents64` to fail.
368 crate::io::dup2(&file_fd, &mut dir.fd).unwrap();
369
370 assert!(matches!(dir.next(), Some(Err(_))));
371 assert!(dir.next().is_none());
372 }
373}
374