1 use crate::fd::{AsFd, BorrowedFd, OwnedFd};
2 use crate::ffi::{CStr, CString};
3 use crate::fs::{
4 fcntl_getfl, fstat, fstatfs, fstatvfs, openat, FileType, Mode, OFlags, Stat, StatFs, StatVfs,
5 };
6 use crate::io;
7 #[cfg(feature = "process")]
8 use crate::process::fchdir;
9 use crate::utils::as_ptr;
10 use alloc::borrow::ToOwned;
11 use alloc::vec::Vec;
12 use core::fmt;
13 use core::mem::size_of;
14 use linux_raw_sys::general::{linux_dirent64, SEEK_SET};
15
16 /// `DIR*`
17 pub 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
34 impl Dir {
35 /// Take ownership of `fd` and construct a `Dir` that reads entries from
36 /// the given directory file descriptor.
37 #[inline]
new<Fd: Into<OwnedFd>>(fd: Fd) -> io::Result<Self>38 pub fn new<Fd: Into<OwnedFd>>(fd: Fd) -> io::Result<Self> {
39 Self::_new(fd.into())
40 }
41
42 #[inline]
_new(fd: OwnedFd) -> io::Result<Self>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]
read_from<Fd: AsFd>(fd: Fd) -> io::Result<Self>56 pub fn read_from<Fd: AsFd>(fd: Fd) -> io::Result<Self> {
57 Self::_read_from(fd.as_fd())
58 }
59
60 #[inline]
_read_from(fd: BorrowedFd<'_>) -> io::Result<Self>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]
rewind(&mut self)76 pub fn rewind(&mut self) {
77 self.any_errors = false;
78 self.rewind = true;
79 self.pos = self.buf.len();
80 }
81
82 /// `readdir(self)`, where `None` means the end of the directory.
read(&mut self) -> Option<io::Result<DirEntry>>83 pub fn read(&mut self) -> Option<io::Result<DirEntry>> {
84 // If we've seen errors, don't continue to try to read anything further.
85 if self.any_errors {
86 return None;
87 }
88
89 // If a rewind was requested, seek to the beginning.
90 if self.rewind {
91 self.rewind = false;
92 match io::retry_on_intr(|| {
93 crate::backend::fs::syscalls::_seek(self.fd.as_fd(), 0, SEEK_SET)
94 }) {
95 Ok(_) => (),
96 Err(err) => {
97 self.any_errors = true;
98 return Some(Err(err));
99 }
100 }
101 }
102
103 // Compute linux_dirent64 field offsets.
104 let z = linux_dirent64 {
105 d_ino: 0_u64,
106 d_off: 0_i64,
107 d_type: 0_u8,
108 d_reclen: 0_u16,
109 d_name: Default::default(),
110 };
111 let base = as_ptr(&z) as usize;
112 let offsetof_d_reclen = (as_ptr(&z.d_reclen) as usize) - base;
113 let offsetof_d_name = (as_ptr(&z.d_name) as usize) - base;
114 let offsetof_d_ino = (as_ptr(&z.d_ino) as usize) - base;
115 let offsetof_d_type = (as_ptr(&z.d_type) as usize) - base;
116
117 // Test if we need more entries, and if so, read more.
118 if self.buf.len() - self.pos < size_of::<linux_dirent64>() {
119 match self.read_more()? {
120 Ok(()) => (),
121 Err(err) => return Some(Err(err)),
122 }
123 }
124
125 // We successfully read an entry. Extract the fields.
126 let pos = self.pos;
127
128 // Do an unaligned u16 load.
129 let d_reclen = u16::from_ne_bytes([
130 self.buf[pos + offsetof_d_reclen],
131 self.buf[pos + offsetof_d_reclen + 1],
132 ]);
133 assert!(self.buf.len() - pos >= d_reclen as usize);
134 self.pos += d_reclen as usize;
135
136 // Read the NUL-terminated name from the `d_name` field. Without
137 // `unsafe`, we need to scan for the NUL twice: once to obtain a size
138 // for the slice, and then once within `CStr::from_bytes_with_nul`.
139 let name_start = pos + offsetof_d_name;
140 let name_len = self.buf[name_start..]
141 .iter()
142 .position(|x| *x == b'\0')
143 .unwrap();
144 let name = CStr::from_bytes_with_nul(&self.buf[name_start..][..=name_len]).unwrap();
145 let name = name.to_owned();
146 assert!(name.as_bytes().len() <= self.buf.len() - name_start);
147
148 // Do an unaligned u64 load.
149 let d_ino = u64::from_ne_bytes([
150 self.buf[pos + offsetof_d_ino],
151 self.buf[pos + offsetof_d_ino + 1],
152 self.buf[pos + offsetof_d_ino + 2],
153 self.buf[pos + offsetof_d_ino + 3],
154 self.buf[pos + offsetof_d_ino + 4],
155 self.buf[pos + offsetof_d_ino + 5],
156 self.buf[pos + offsetof_d_ino + 6],
157 self.buf[pos + offsetof_d_ino + 7],
158 ]);
159
160 let d_type = self.buf[pos + offsetof_d_type];
161
162 // Check that our types correspond to the `linux_dirent64` types.
163 let _ = linux_dirent64 {
164 d_ino,
165 d_off: 0,
166 d_type,
167 d_reclen,
168 d_name: Default::default(),
169 };
170
171 Some(Ok(DirEntry {
172 d_ino,
173 d_type,
174 name,
175 }))
176 }
177
178 #[must_use]
read_more(&mut self) -> Option<io::Result<()>>179 fn read_more(&mut self) -> Option<io::Result<()>> {
180 // The first few times we're called, we allocate a relatively small
181 // buffer, because many directories are small. If we're called more,
182 // use progressively larger allocations, up to a fixed maximum.
183 //
184 // The specific sizes and policy here have not been tuned in detail yet
185 // and may need to be adjusted. In doing so, we should be careful to
186 // avoid unbounded buffer growth. This buffer only exists to share the
187 // cost of a `getdents` call over many entries, so if it gets too big,
188 // cache and heap usage will outweigh the benefit. And ultimately,
189 // directories can contain more entries than we can allocate contiguous
190 // memory for, so we'll always need to cap the size at some point.
191 if self.buf.len() < 1024 * size_of::<linux_dirent64>() {
192 self.buf.reserve(32 * size_of::<linux_dirent64>());
193 }
194 self.buf.resize(self.buf.capacity(), 0);
195 let nread = match io::retry_on_intr(|| {
196 crate::backend::fs::syscalls::getdents(self.fd.as_fd(), &mut self.buf)
197 }) {
198 Ok(nread) => nread,
199 Err(io::Errno::NOENT) => {
200 self.any_errors = true;
201 return None;
202 }
203 Err(err) => {
204 self.any_errors = true;
205 return Some(Err(err));
206 }
207 };
208 self.buf.resize(nread, 0);
209 self.pos = 0;
210 if nread == 0 {
211 None
212 } else {
213 Some(Ok(()))
214 }
215 }
216
217 /// `fstat(self)`
218 #[inline]
stat(&self) -> io::Result<Stat>219 pub fn stat(&self) -> io::Result<Stat> {
220 fstat(&self.fd)
221 }
222
223 /// `fstatfs(self)`
224 #[inline]
statfs(&self) -> io::Result<StatFs>225 pub fn statfs(&self) -> io::Result<StatFs> {
226 fstatfs(&self.fd)
227 }
228
229 /// `fstatvfs(self)`
230 #[inline]
statvfs(&self) -> io::Result<StatVfs>231 pub fn statvfs(&self) -> io::Result<StatVfs> {
232 fstatvfs(&self.fd)
233 }
234
235 /// `fchdir(self)`
236 #[cfg(feature = "process")]
237 #[cfg_attr(doc_cfg, doc(cfg(feature = "process")))]
238 #[inline]
chdir(&self) -> io::Result<()>239 pub fn chdir(&self) -> io::Result<()> {
240 fchdir(&self.fd)
241 }
242 }
243
244 impl Iterator for Dir {
245 type Item = io::Result<DirEntry>;
246
247 #[inline]
next(&mut self) -> Option<Self::Item>248 fn next(&mut self) -> Option<Self::Item> {
249 Self::read(self)
250 }
251 }
252
253 impl fmt::Debug for Dir {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result254 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
255 f.debug_struct("Dir").field("fd", &self.fd).finish()
256 }
257 }
258
259 /// `struct dirent`
260 #[derive(Debug)]
261 pub struct DirEntry {
262 d_ino: u64,
263 d_type: u8,
264 name: CString,
265 }
266
267 impl DirEntry {
268 /// Returns the file name of this directory entry.
269 #[inline]
file_name(&self) -> &CStr270 pub fn file_name(&self) -> &CStr {
271 &self.name
272 }
273
274 /// Returns the type of this directory entry.
275 #[inline]
file_type(&self) -> FileType276 pub fn file_type(&self) -> FileType {
277 FileType::from_dirent_d_type(self.d_type)
278 }
279
280 /// Return the inode number of this directory entry.
281 #[inline]
ino(&self) -> u64282 pub fn ino(&self) -> u64 {
283 self.d_ino
284 }
285 }
286
287 #[test]
dir_iterator_handles_io_errors()288 fn dir_iterator_handles_io_errors() {
289 // create a dir, keep the FD, then delete the dir
290 let tmp = tempfile::tempdir().unwrap();
291 let fd = crate::fs::openat(
292 crate::fs::CWD,
293 tmp.path(),
294 crate::fs::OFlags::RDONLY | crate::fs::OFlags::CLOEXEC,
295 crate::fs::Mode::empty(),
296 )
297 .unwrap();
298
299 let file_fd = crate::fs::openat(
300 &fd,
301 tmp.path().join("test.txt"),
302 crate::fs::OFlags::WRONLY | crate::fs::OFlags::CREATE,
303 crate::fs::Mode::RWXU,
304 )
305 .unwrap();
306
307 let mut dir = Dir::read_from(&fd).unwrap();
308
309 // Reach inside the `Dir` and replace its directory with a file, which
310 // will cause the subsequent `getdents64` to fail.
311 crate::io::dup2(&file_fd, &mut dir.fd).unwrap();
312
313 assert!(matches!(dir.next(), Some(Err(_))));
314 assert!(dir.next().is_none());
315 }
316