Fix Mode::from_raw_mode to mask out the S_IFMT bits. (#1124)

The `S_IFMT` bits in a `st_mode` field value hold the file type; mask
them out when converting the value to a `Mode`. `Mode` can tolerate
bits it doesn't recognize, however this does prevent it from being
compared for equality in the obvious way.

Fixes #1104.

Author: sunfishcode

src/backend/libc/fs/types.rs

@@ -162,7 +162,7 @@ impl Mode {
     /// `Mode`.
     #[inline]
     pub const fn from_raw_mode(st_mode: RawMode) -> Self {
-        Self::from_bits_truncate(st_mode)
+        Self::from_bits_truncate(st_mode & !c::S_IFMT as RawMode)
     }
 
     /// Construct an `st_mode` value from a `Mode`.

src/backend/linux_raw/fs/types.rs

@@ -130,7 +130,7 @@ impl Mode {
     /// `Mode`.
     #[inline]
     pub const fn from_raw_mode(st_mode: RawMode) -> Self {
-        Self::from_bits_truncate(st_mode)
+        Self::from_bits_truncate(st_mode & !linux_raw_sys::general::S_IFMT)
     }
 
     /// Construct an `st_mode` value from a `Mode`.

tests/fs/file.rs

@@ -185,3 +185,16 @@ fn test_setfl_append() {
     assert_eq!(rustix::io::read(&file, &mut buf), Ok(19));
     assert_eq!(&buf, b"uvwdefghijklmnopxyz\0\0\0\0\0\0\0\0\0\0\0\0\0");
 }
+
+#[test]
+fn test_mode() {
+    use rustix::fs::{Mode, RawMode};
+
+    let mode = Mode::from_raw_mode((libc::S_IFSOCK | libc::S_IRUSR) as RawMode);
+    assert_eq!(mode, Mode::RUSR);
+    assert_eq!(mode.bits(), libc::S_IRUSR as RawMode);
+
+    let mode = Mode::from_raw_mode((libc::S_IFSOCK | libc::S_IRWXU) as RawMode);
+    assert_eq!(mode, Mode::RWXU);
+    assert_eq!(mode.bits(), libc::S_IRWXU as RawMode);
+}