Add code that reads a file from the ESP

rust/src/main.rs

@@ -2,9 +2,24 @@
 #![no_std]
 #![feature(abi_efiapi)]
 
-use uefi::{prelude::*, proto::console::text::Output};
+extern crate alloc;
 
-mod boot_image;
+use core::ops::Deref;
+use log::debug;
+use uefi::{
+    prelude::*,
+    proto::{
+        console::text::Output,
+        device_path::DevicePath,
+        loaded_image::LoadedImage,
+        media::{
+            file::{Directory, File, FileAttribute, FileMode},
+            fs::SimpleFileSystem,
+        },
+    },
+    table::boot::{OpenProtocolAttributes, OpenProtocolParams},
+    Result,
+};
 
 fn print_logo(output: &mut Output) {
     output.clear().unwrap();
@@ -23,11 +38,73 @@ fn print_logo(output: &mut Output) {
         .unwrap();
 }
 
+// # Safety
+//
+// TODO Need to find out whether we can open the protocols in safe code.
+unsafe fn root_directory(image: Handle, boot_services: &BootServices) -> Result<Directory> {
+    let loaded_image = boot_services.open_protocol::<LoadedImage>(
+        OpenProtocolParams {
+            handle: image,
+            agent: image,
+            controller: None,
+        },
+        OpenProtocolAttributes::Exclusive,
+    )?;
+
+    let device_handle = loaded_image.device();
+
+    let device_path = boot_services.open_protocol::<DevicePath>(
+        OpenProtocolParams {
+            handle: device_handle,
+            agent: image,
+            controller: None,
+        },
+        OpenProtocolAttributes::Exclusive,
+    )?;
+
+    let mut device_path: &DevicePath = device_path.deref();
+    let fs_handle = boot_services.locate_device_path::<SimpleFileSystem>(&mut device_path)?;
+
+    let mut file_system_raw = boot_services.open_protocol::<SimpleFileSystem>(
+        OpenProtocolParams {
+            handle: fs_handle,
+            agent: image,
+            controller: None,
+        },
+        OpenProtocolAttributes::Exclusive,
+    )?;
+
+    let file_system: &mut SimpleFileSystem = &mut file_system_raw;
+    let root = file_system.open_volume()?;
+
+    Ok(root)
+}
+
 #[entry]
-fn main(_handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
+fn main(handle: Handle, mut system_table: SystemTable<Boot>) -> Status {
     uefi_services::init(&mut system_table).unwrap();
 
     print_logo(system_table.stdout());
 
+    let boot_services = system_table.boot_services();
+    let mut root = unsafe { root_directory(handle, boot_services).unwrap() };
+
+    debug!("Found root");
+
+    let mut file = root
+        .open(cstr16!("foo.txt"), FileMode::Read, FileAttribute::empty())
+        .unwrap()
+        .into_regular_file()
+        .unwrap();
+
+    debug!("Opened file");
+
+    let mut buf = [0; 512];
+
+    let bytes_read = file.read(&mut buf).unwrap();
+    let data = &buf[0..bytes_read];
+
+    debug!("Data: {}", alloc::str::from_utf8(&data).unwrap());
+
     Status::SUCCESS
 }