[pbs-devel] [PATCH v4 proxmox 1/3] sys: add function to get boot_mode

[Gabriel Goller <g.goller@proxmox.com>]

Helper that returns the current boot_mode. Either EFI, BIOS, or EFI
(Secure Boot).
Detection works the same as in pve, we use `/sys/firmware/efi` and
the `efivars/SecureBoot-xxx..` file.

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
 proxmox-sys/src/boot_mode.rs | 54 ++++++++++++++++++++++++++++++++++++
 proxmox-sys/src/lib.rs       |  1 +
 2 files changed, 55 insertions(+)
 create mode 100644 proxmox-sys/src/boot_mode.rs

diff --git a/proxmox-sys/src/boot_mode.rs b/proxmox-sys/src/boot_mode.rs
new file mode 100644
index 0000000..6dcdf07
--- /dev/null
+++ b/proxmox-sys/src/boot_mode.rs
@@ -0,0 +1,54 @@
+use std::{io::Read, sync::Mutex};
+
+#[derive(Clone, Copy)]
+pub enum SecureBoot {
+    /// SecureBoot is enabled
+    Enabled,
+    /// SecureBoot is disabled
+    Disabled,
+}
+
+/// The possible BootModes
+#[derive(Clone, Copy)]
+pub enum BootModeInformation {
+    /// The BootMode is EFI/UEFI, has a SecureBoot variant
+    Efi(SecureBoot),
+    /// The BootMode is Legacy BIOS
+    Bios,
+}
+
+// Returns the current bootmode (BIOS, EFI, or EFI(Secure Boot))
+pub fn boot_mode() -> BootModeInformation {
+    lazy_static::lazy_static!(
+        static ref BOOT_MODE: Mutex<Option<BootModeInformation>> = Mutex::new(None);
+    );
+
+    let mut last = BOOT_MODE.lock().unwrap();
+    let value = last.or_else(|| {
+        if std::path::Path::new("/sys/firmware/efi").exists() {
+            // Check if SecureBoot is enabled
+            // Attention: this file is not seekable!
+            // Spec: https://uefi.org/specs/UEFI/2.10/03_Boot_Manager.html?highlight=8be4d#globally-defined-variables
+            let efivar = std::fs::File::open(
+                "/sys/firmware/efi/efivars/SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c",
+            );
+            if let Ok(mut file) = efivar {
+                let mut buf = [0; 5];
+                let Ok(_) = file.read_exact(&mut buf) else {
+                    return Some(BootModeInformation::Efi(SecureBoot::Disabled));
+                };
+                if buf[4..] == [1] {
+                    Some(BootModeInformation::Efi(SecureBoot::Enabled))
+                } else {
+                    Some(BootModeInformation::Efi(SecureBoot::Disabled))
+                }
+            } else {
+                Some(BootModeInformation::Efi(SecureBoot::Disabled))
+            }
+        } else {
+            Some(BootModeInformation::Bios)
+        }
+    });
+    *last = value;
+    value.unwrap()
+}
diff --git a/proxmox-sys/src/lib.rs b/proxmox-sys/src/lib.rs
index 7e59058..8ea7073 100644
--- a/proxmox-sys/src/lib.rs
+++ b/proxmox-sys/src/lib.rs
@@ -1,5 +1,6 @@
 use std::os::unix::ffi::OsStrExt;
 
+pub mod boot_mode;
 pub mod command;
 #[cfg(feature = "crypt")]
 pub mod crypt;
-- 
2.39.2