boot: Add freestanding get_image_file_system

Author: nicholasbishop

uefi/src/boot.rs

@@ -5,6 +5,8 @@
 use crate::data_types::PhysicalAddress;
 use crate::mem::memory_map::{MemoryMapBackingMemory, MemoryMapKey, MemoryMapMeta, MemoryMapOwned};
 use crate::proto::device_path::DevicePath;
+use crate::proto::loaded_image::LoadedImage;
+use crate::proto::media::fs::SimpleFileSystem;
 use crate::proto::{Protocol, ProtocolPointer};
 use crate::table::Revision;
 use crate::util::opt_nonnull_to_ptr;
@@ -17,10 +19,7 @@ use uefi::{table, Char16, Error, Event, Guid, Handle, Result, Status, StatusExt}
 use uefi_raw::table::boot::InterfaceType;
 
 #[cfg(doc)]
-use {
-    crate::proto::device_path::LoadedImageDevicePath, crate::proto::loaded_image::LoadedImage,
-    crate::proto::media::fs::SimpleFileSystem,
-};
+use crate::proto::device_path::LoadedImageDevicePath;
 
 pub use uefi::table::boot::{
     AllocateType, EventNotifyFn, LoadImageSource, OpenProtocolAttributes, OpenProtocolParams,
@@ -1069,6 +1068,35 @@ pub fn stall(microseconds: usize) {
     }
 }
 
+/// Retrieves a [`SimpleFileSystem`] protocol associated with the device the given
+/// image was loaded from.
+///
+/// # Errors
+///
+/// This function can return errors from [`open_protocol_exclusive`] and
+/// [`locate_device_path`]. See those functions for more details.
+///
+/// [`open_protocol_exclusive`]: Self::open_protocol_exclusive
+/// [`locate_device_path`]: Self::locate_device_path
+///
+/// * [`Status::INVALID_PARAMETER`]
+/// * [`Status::UNSUPPORTED`]
+/// * [`Status::ACCESS_DENIED`]
+/// * [`Status::ALREADY_STARTED`]
+/// * [`Status::NOT_FOUND`]
+pub fn get_image_file_system(image_handle: Handle) -> Result<ScopedProtocol<SimpleFileSystem>> {
+    let loaded_image = open_protocol_exclusive::<LoadedImage>(image_handle)?;
+
+    let device_handle = loaded_image
+        .device()
+        .ok_or(Error::new(Status::UNSUPPORTED, ()))?;
+    let device_path = open_protocol_exclusive::<DevicePath>(device_handle)?;
+
+    let device_handle = locate_device_path::<SimpleFileSystem>(&mut &*device_path)?;
+
+    open_protocol_exclusive(device_handle)
+}
+
 /// Protocol interface [`Guids`][Guid] that are installed on a [`Handle`] as
 /// returned by [`protocols_per_handle`].
 #[derive(Debug)]