Add system::stdout_handle() accessor

Provides direct access to the stdout handle from the system table.
This complements the existing with_stdout() function, which only
exposes the Output protocol. Having the handle is useful for opening
additional protocols on the console device or passing it to UEFI
functions that require a device handle.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

uefi/CHANGELOG.md

@@ -1,6 +1,7 @@
 # uefi - [Unreleased]
 
 ## Added
+- Added `system::stdout_handle()`.
 - Added `proto::ata::AtaRequestBuilder::read_pio()`.
 - Added `proto::shell::Shell::{var(), set_var(), vars()}`
 - Added `proto::pci::root_bridge::PciRootBridgeIo::configuration()`.

uefi/src/system.rs

@@ -12,7 +12,7 @@
 use crate::proto::console::text::{Input, Output};
 use crate::table::cfg::ConfigTableEntry;
 use crate::table::{self, Revision};
-use crate::{CStr16, Char16};
+use crate::{CStr16, Char16, Handle};
 use core::slice;
 
 /// Get the firmware vendor string.
@@ -139,6 +139,23 @@ where
     f(stdout)
 }
 
+/// Get the [`Handle`] associated with stdout.
+///
+/// # Panics
+///
+/// This function will panic if called after exiting boot services, or if stdout
+/// is not available.
+#[must_use]
+pub fn stdout_handle() -> Handle {
+    let st = table::system_table_raw_panicking();
+    // SAFETY: valid per requirements of `set_system_table`.
+    let st = unsafe { st.as_ref() };
+    // The I/O protocols cannot be used after exiting boot services.
+    assert!(!st.boot_services.is_null(), "boot services are not active");
+    // SAFETY: stdout_handle is a valid handle per UEFI specification.
+    unsafe { Handle::from_ptr(st.stdout_handle) }.expect("stdout is not available")
+}
+
 /// Call `f` with the [`Output`] protocol attached to stderr.
 ///
 /// # Panics