feat(bls): basic support for boot loader interface

src/integrations/bootloader_interface.rs

@@ -1,10 +1,14 @@
-use anyhow::Result;
-use uefi::Guid;
+use anyhow::{Context, Result};
+use uefi::{CString16, Guid, guid};
+use uefi_raw::table::runtime::{VariableAttributes, VariableVendor};
 
 /// Bootloader Interface support.
 pub struct BootloaderInterface;
 
 impl BootloaderInterface {
+    /// Bootloader Interface GUID from https://systemd.io/BOOT_LOADER_INTERFACE
+    const VENDOR: VariableVendor = VariableVendor(guid!("4a67b082-0a4c-41cf-b6c7-440b29bb8c4f"));
+
     /// Tell the system that Sprout was initialized at the current time.
     pub fn mark_init() -> Result<()> {
         // TODO(azenla): Implement support for LoaderTimeInitUSec here.
@@ -18,26 +22,54 @@ impl BootloaderInterface {
     }
 
     /// Tell the system what the partition GUID of the ESP Sprout was booted from is.
-    pub fn set_partition_guid(_guid: &Guid) -> Result<()> {
-        // TODO(azenla): Implement support for LoaderDevicePartUUID here.
-        Ok(())
+    pub fn set_partition_guid(guid: &Guid) -> Result<()> {
+        Self::set_cstr16("LoaderDevicePartUUID", &guid.to_string())
     }
 
     /// Tell the system what boot entries are available.
-    pub fn set_entries<N: AsRef<str>>(_entries: impl Iterator<Item = N>) -> Result<()> {
-        // TODO(azenla): Implement support for LoaderEntries here.
-        Ok(())
+    pub fn set_entries<N: AsRef<str>>(entries: impl Iterator<Item = N>) -> Result<()> {
+        // Entries are stored as a null-terminated list of CString16 strings back to back.
+        // Iterate over the entries and convert them to CString16 placing them into data.
+        let mut data = Vec::new();
+        for entry in entries {
+            // Convert the entry to a CString16.
+            let entry = CString16::try_from(entry.as_ref())
+                .context("unable to convert entry to CString16")?;
+            // Write the bytes (including the null terminator) into the data buffer.
+            data.extend_from_slice(entry.as_bytes());
+        }
+        Self::set("LoaderEntries", &data)
     }
 
     /// Tell the system what the default boot entry is.
-    pub fn set_default_entry(_entry: String) -> Result<()> {
-        // TODO(azenla): Implement support for LoaderEntryDefault here.
-        Ok(())
+    pub fn set_default_entry(entry: String) -> Result<()> {
+        Self::set_cstr16("LoaderEntryDefault", &entry)
     }
 
     /// Tell the system what the selected boot entry is.
-    pub fn set_selected_entry(_entry: String) -> Result<()> {
-        // TODO(azenla): Implement support for LoaderEntrySelected here.
+    pub fn set_selected_entry(entry: String) -> Result<()> {
+        Self::set_cstr16("LoaderEntrySelected", &entry)
+    }
+
+    /// The [VariableAttributes] for bootloader interface variables.
+    fn attributes() -> VariableAttributes {
+        VariableAttributes::BOOTSERVICE_ACCESS | VariableAttributes::RUNTIME_ACCESS
+    }
+
+    /// Set a bootloader interface variable specified by `key` to `value`.
+    fn set(key: &str, value: &[u8]) -> Result<()> {
+        let name =
+            CString16::try_from(key).context("unable to convert variable name to CString16")?;
+        uefi::runtime::set_variable(&name, &Self::VENDOR, Self::attributes(), value)
+            .with_context(|| format!("unable to set efi variable {}", key))?;
         Ok(())
     }
+
+    /// Set a bootloader interface variable specified by `key` to `value`, converting the value to
+    /// a [CString16].
+    fn set_cstr16(key: &str, value: &str) -> Result<()> {
+        let value =
+            CString16::try_from(value).context("unable to convert variable value to CString16")?;
+        Self::set(key, value.as_bytes())
+    }
 }