Don't set O_LARGEFILE on openat2 when O_PATH is set. (#703)

Linux appears to reject `O_LARGEFILE` with `O_PATH` in `openat2`,
so avoid that combination.

Author: sunfishcode

src/backend/linux_raw/fs/syscalls.rs

@@ -78,12 +78,15 @@ pub(crate) fn openat(
 pub(crate) fn openat2(
     dirfd: BorrowedFd<'_>,
     path: &CStr,
-    flags: OFlags,
+    mut flags: OFlags,
     mode: Mode,
     resolve: ResolveFlags,
 ) -> io::Result<OwnedFd> {
-    // Always enable support for large files.
-    let flags = flags | OFlags::from_bits_retain(c::O_LARGEFILE);
+    // Enable support for large files, but not with `O_PATH` because
+    // `openat2` doesn't like those flags together.
+    if !flags.contains(OFlags::PATH) {
+        flags = flags | OFlags::from_bits_retain(c::O_LARGEFILE);
+    }
 
     unsafe {
         ret_owned_fd(syscall_readonly!(

tests/fs/openat2.rs

@@ -75,6 +75,16 @@ fn test_openat2() {
     )
     .unwrap_err();
 
+    // Test with `O_PATH`.
+    let _ = openat2_more(
+        &dir,
+        "test.txt",
+        OFlags::RDONLY | OFlags::CLOEXEC | OFlags::PATH,
+        Mode::empty(),
+        ResolveFlags::empty(),
+    )
+    .unwrap();
+
     // Test `NO_MAGICLINKS`.
     let test = openat2_more(
         &dir,