fix(ext/node): stub cpu_info() for OpenBSD (#25807)

Add an implementation of cpu_info() for OpenBSD, that returns a
correctly-sized array. Since Rust's libc bindings for OpenBSD do not
contain all symbols necessary for a full implementation and it is not
planned to add them, this solution at least avoids problems with code
that relies on cpu_info() purely for the size of the returned array to
derive the number of available CPUs.

This addresses https://github.com/denoland/deno/issues/25621

ext/node/ops/os/cpus.rs

@@ -294,6 +294,54 @@ pub fn cpu_info() -> Option<Vec<CpuInfo>> {
   Some(cpus)
 }
 
+#[cfg(target_os = "openbsd")]
+pub fn cpu_info() -> Option<Vec<CpuInfo>> {
+  // Stub implementation for OpenBSD that returns an array of the correct size
+  // but with dummy values.
+  // Rust's OpenBSD libc bindings don't contain all the symbols needed for a
+  // full implementation, and including them is not planned.
+  let mut mib = [libc::CTL_HW, libc::HW_NCPUONLINE];
+
+  // SAFETY: Assumes correct behavior of platform-specific
+  // sysctls and data structures. Relies on specific sysctl
+  // names and parameter existence.
+  unsafe {
+    let mut ncpu: libc::c_uint = 0;
+    let mut size = std::mem::size_of_val(&ncpu) as libc::size_t;
+
+    // Get number of CPUs online
+    let res = libc::sysctl(
+      mib.as_mut_ptr(),
+      mib.len() as _,
+      &mut ncpu as *mut _ as *mut _,
+      &mut size,
+      std::ptr::null_mut(),
+      0,
+    );
+    // If res == 0, the sysctl call was succesful and
+    // ncpuonline contains the number of online CPUs.
+    if res != 0 {
+      return None;
+    } else {
+      let mut cpus = vec![CpuInfo::new(); ncpu as usize];
+
+      for (_, cpu) in cpus.iter_mut().enumerate() {
+        cpu.model = "Undisclosed CPU".to_string();
+        // Return 1 as a dummy value so the tests won't
+        // fail.
+        cpu.speed = 1;
+        cpu.times.user = 1;
+        cpu.times.nice = 1;
+        cpu.times.sys = 1;
+        cpu.times.idle = 1;
+        cpu.times.irq = 1;
+      }
+
+      return Some(cpus);
+    }
+  }
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;