uefi: fs: Implement exists

Also adds the initial file abstractions.

The file opening algorithm is inspired from UEFI shell. It starts by
classifying if the Path is Shell mapping, text representation of device
path protocol, or a relative path and converts into an absolute text
representation of device path protocol.

After that, it queries all handles supporting
EFI_SIMPLE_FILE_SYSTEM_PROTOCOL and opens the volume that matches the
device path protocol prefix (similar to Windows drive). After that, it
opens the file in the volume using the remaining pat.

It also introduces OwnedDevicePath and BorrowedDevicePath abstractions
to allow working with the base UEFI and Shell device paths efficiently.

DevicePath in UEFI behaves like an a group of nodes laied out in the
memory contiguously and thus can be modeled using iterators.

Signed-off-by: Ayush Singh <[email protected]>

Author: Ayush1325

library/std/src/sys/pal/uefi/fs.rs

@@ -311,8 +311,13 @@ pub fn remove_dir_all(_path: &Path) -> io::Result<()> {
     unsupported()
 }
 
-pub fn exists(_path: &Path) -> io::Result<bool> {
-    unsupported()
+pub fn exists(path: &Path) -> io::Result<bool> {
+    let f = uefi_fs::File::from_path(path, r_efi::protocols::file::MODE_READ, 0);
+    match f {
+        Ok(_) => Ok(true),
+        Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(false),
+        Err(e) => Err(e),
+    }
 }
 
 pub fn readlink(_p: &Path) -> io::Result<PathBuf> {
@@ -342,3 +347,122 @@ pub fn canonicalize(_p: &Path) -> io::Result<PathBuf> {
 pub fn copy(_from: &Path, _to: &Path) -> io::Result<u64> {
     unsupported()
 }
+
+mod uefi_fs {
+    use r_efi::protocols::{device_path, file, simple_file_system};
+
+    use super::super::helpers;
+    use crate::boxed::Box;
+    use crate::io;
+    use crate::mem::MaybeUninit;
+    use crate::path::Path;
+    use crate::ptr::NonNull;
+
+    pub(crate) struct File(NonNull<file::Protocol>);
+
+    impl File {
+        pub(crate) fn from_path(path: &Path, open_mode: u64, attr: u64) -> io::Result<Self> {
+            let absoulte = crate::path::absolute(path)?;
+
+            let p = helpers::OwnedDevicePath::from_text(absoulte.as_os_str())?;
+            let (vol, mut path_remaining) = Self::open_volume_from_device_path(p.borrow())?;
+
+            vol.open(&mut path_remaining, open_mode, attr)
+        }
+
+        fn open_volume_from_device_path(
+            path: helpers::BorrowedDevicePath<'_>,
+        ) -> io::Result<(Self, Box<[u16]>)> {
+            let handles = match helpers::locate_handles(simple_file_system::PROTOCOL_GUID) {
+                Ok(x) => x,
+                Err(e) => return Err(e),
+            };
+            for handle in handles {
+                let volume_device_path: NonNull<device_path::Protocol> =
+                    match helpers::open_protocol(handle, device_path::PROTOCOL_GUID) {
+                        Ok(x) => x,
+                        Err(_) => continue,
+                    };
+                let volume_device_path = helpers::BorrowedDevicePath::new(volume_device_path);
+
+                if let Some(left_path) = path_best_match(&volume_device_path, &path) {
+                    return Ok((Self::open_volume(handle)?, left_path));
+                }
+            }
+
+            Err(io::const_error!(io::ErrorKind::NotFound, "Volume Not Found"))
+        }
+
+        // Open volume on device_handle using SIMPLE_FILE_SYSTEM_PROTOCOL
+        fn open_volume(device_handle: NonNull<crate::ffi::c_void>) -> io::Result<Self> {
+            let simple_file_system_protocol = helpers::open_protocol::<simple_file_system::Protocol>(
+                device_handle,
+                simple_file_system::PROTOCOL_GUID,
+            )?;
+
+            let mut file_protocol: MaybeUninit<*mut file::Protocol> = MaybeUninit::uninit();
+            let r = unsafe {
+                ((*simple_file_system_protocol.as_ptr()).open_volume)(
+                    simple_file_system_protocol.as_ptr(),
+                    file_protocol.as_mut_ptr(),
+                )
+            };
+            if r.is_error() {
+                return Err(io::Error::from_raw_os_error(r.as_usize()));
+            }
+
+            // Since no error was returned, file protocol should be non-NULL.
+            let p = NonNull::new(unsafe { file_protocol.assume_init() }).unwrap();
+            Ok(Self(p))
+        }
+
+        fn open(&self, path: &mut [u16], open_mode: u64, attr: u64) -> io::Result<Self> {
+            let file_ptr = self.0.as_ptr();
+            let mut file_opened: MaybeUninit<*mut file::Protocol> = MaybeUninit::uninit();
+
+            let r = unsafe {
+                ((*file_ptr).open)(
+                    file_ptr,
+                    file_opened.as_mut_ptr(),
+                    path.as_mut_ptr(),
+                    open_mode,
+                    attr,
+                )
+            };
+
+            if r.is_error() {
+                return Err(io::Error::from_raw_os_error(r.as_usize()));
+            }
+
+            // Since no error was returned, file protocol should be non-NULL.
+            let p = NonNull::new(unsafe { file_opened.assume_init() }).unwrap();
+            Ok(File(p))
+        }
+    }
+
+    impl Drop for File {
+        fn drop(&mut self) {
+            let file_ptr = self.0.as_ptr();
+            let _ = unsafe { ((*self.0.as_ptr()).close)(file_ptr) };
+        }
+    }
+
+    fn path_best_match<'a>(
+        source: &helpers::BorrowedDevicePath<'a>,
+        target: &helpers::BorrowedDevicePath<'a>,
+    ) -> Option<Box<[u16]>> {
+        let mut source_iter = source.iter().take_while(|x| !x.is_end_instance());
+        let mut target_iter = target.iter().take_while(|x| !x.is_end_instance());
+
+        loop {
+            match (source_iter.next(), target_iter.next()) {
+                (Some(x), Some(y)) if x == y => continue,
+                (None, Some(y)) => {
+                    let p = y.to_path().to_text().ok()?;
+                    return helpers::os_string_to_raw(&p);
+                }
+                _ => return None,
+            }
+        }
+    }
+}

library/std/src/sys/pal/uefi/helpers.rs

@@ -14,6 +14,7 @@ use r_efi::protocols::{device_path, device_path_to_text, shell};
 
 use crate::ffi::{OsStr, OsString};
 use crate::io::{self, const_error};
+use crate::iter::Iterator;
 use crate::marker::PhantomData;
 use crate::mem::{MaybeUninit, size_of};
 use crate::os::uefi::env::boot_services;
@@ -216,6 +217,60 @@ pub(crate) fn device_path_to_text(path: NonNull<device_path::Protocol>) -> io::R
     Err(io::const_error!(io::ErrorKind::NotFound, "No device path to text protocol found"))
 }
 
+fn device_node_to_text(path: NonNull<device_path::Protocol>) -> io::Result<OsString> {
+    fn node_to_text(
+        protocol: NonNull<device_path_to_text::Protocol>,
+        path: NonNull<device_path::Protocol>,
+    ) -> io::Result<OsString> {
+        let path_ptr: *mut r_efi::efi::Char16 = unsafe {
+            ((*protocol.as_ptr()).convert_device_node_to_text)(
+                path.as_ptr(),
+                // DisplayOnly
+                r_efi::efi::Boolean::FALSE,
+                // AllowShortcuts
+                r_efi::efi::Boolean::FALSE,
+            )
+        };
+
+        let path = os_string_from_raw(path_ptr)
+            .ok_or(io::const_error!(io::ErrorKind::InvalidData, "Invalid path"))?;
+
+        if let Some(boot_services) = crate::os::uefi::env::boot_services() {
+            let boot_services: NonNull<r_efi::efi::BootServices> = boot_services.cast();
+            unsafe {
+                ((*boot_services.as_ptr()).free_pool)(path_ptr.cast());
+            }
+        }
+
+        Ok(path)
+    }
+
+    static LAST_VALID_HANDLE: AtomicPtr<crate::ffi::c_void> =
+        AtomicPtr::new(crate::ptr::null_mut());
+
+    if let Some(handle) = NonNull::new(LAST_VALID_HANDLE.load(Ordering::Acquire)) {
+        if let Ok(protocol) = open_protocol::<device_path_to_text::Protocol>(
+            handle,
+            device_path_to_text::PROTOCOL_GUID,
+        ) {
+            return node_to_text(protocol, path);
+        }
+    }
+
+    let device_path_to_text_handles = locate_handles(device_path_to_text::PROTOCOL_GUID)?;
+    for handle in device_path_to_text_handles {
+        if let Ok(protocol) = open_protocol::<device_path_to_text::Protocol>(
+            handle,
+            device_path_to_text::PROTOCOL_GUID,
+        ) {
+            LAST_VALID_HANDLE.store(handle.as_ptr(), Ordering::Release);
+            return node_to_text(protocol, path);
+        }
+    }
+
+    Err(io::const_error!(io::ErrorKind::NotFound, "No device path to text protocol found"))
+}
+
 /// Gets RuntimeServices.
 pub(crate) fn runtime_services() -> Option<NonNull<r_efi::efi::RuntimeServices>> {
     let system_table: NonNull<r_efi::efi::SystemTable> =
@@ -316,6 +371,10 @@ impl<'a> BorrowedDevicePath<'a> {
         Self { protocol, phantom: PhantomData }
     }
 
+    pub(crate) const fn iter(&'a self) -> DevicePathIterator<'a> {
+        DevicePathIterator::new(DevicePathNode::new(self.protocol))
+    }
+
     pub(crate) fn to_text(&self) -> io::Result<OsString> {
         device_path_to_text(self.protocol)
     }
@@ -330,6 +389,99 @@ impl<'a> crate::fmt::Debug for BorrowedDevicePath<'a> {
     }
 }
 
+pub(crate) struct DevicePathIterator<'a>(Option<DevicePathNode<'a>>);
+
+impl<'a> DevicePathIterator<'a> {
+    const fn new(node: DevicePathNode<'a>) -> Self {
+        if node.is_end() { Self(None) } else { Self(Some(node)) }
+    }
+}
+
+impl<'a> Iterator for DevicePathIterator<'a> {
+    type Item = DevicePathNode<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let cur_node = self.0?;
+
+        let next_node = unsafe { cur_node.next_node() };
+        self.0 = if next_node.is_end() { None } else { Some(next_node) };
+
+        Some(cur_node)
+    }
+}
+
+#[derive(Copy, Clone)]
+pub(crate) struct DevicePathNode<'a> {
+    protocol: NonNull<r_efi::protocols::device_path::Protocol>,
+    phantom: PhantomData<&'a r_efi::protocols::device_path::Protocol>,
+}
+
+impl<'a> DevicePathNode<'a> {
+    pub(crate) const fn new(protocol: NonNull<r_efi::protocols::device_path::Protocol>) -> Self {
+        Self { protocol, phantom: PhantomData }
+    }
+
+    pub(crate) const fn length(&self) -> u16 {
+        let len = unsafe { (*self.protocol.as_ptr()).length };
+        u16::from_le_bytes(len)
+    }
+
+    pub(crate) const fn node_type(&self) -> u8 {
+        unsafe { (*self.protocol.as_ptr()).r#type }
+    }
+
+    pub(crate) const fn sub_type(&self) -> u8 {
+        unsafe { (*self.protocol.as_ptr()).sub_type }
+    }
+
+    pub(crate) const fn is_end(&self) -> bool {
+        self.node_type() == r_efi::protocols::device_path::TYPE_END
+            && self.sub_type() == r_efi::protocols::device_path::End::SUBTYPE_ENTIRE
+    }
+
+    pub(crate) const fn is_end_instance(&self) -> bool {
+        self.node_type() == r_efi::protocols::device_path::TYPE_END
+            && self.sub_type() == r_efi::protocols::device_path::End::SUBTYPE_INSTANCE
+    }
+
+    pub(crate) unsafe fn next_node(&self) -> Self {
+        let node = unsafe {
+            self.protocol
+                .cast::<u8>()
+                .add(self.length().into())
+                .cast::<r_efi::protocols::device_path::Protocol>()
+        };
+        Self::new(node)
+    }
+
+    pub(crate) fn to_path(&'a self) -> BorrowedDevicePath<'a> {
+        BorrowedDevicePath::new(self.protocol)
+    }
+}
+
+impl<'a> PartialEq for DevicePathNode<'a> {
+    fn eq(&self, other: &Self) -> bool {
+        let self_len = self.length();
+        let other_len = other.length();
+
+        self_len == other_len
+            && unsafe {
+                compiler_builtins::mem::memcmp(
+                    self.protocol.as_ptr().cast(),
+                    other.protocol.as_ptr().cast(),
+                    usize::from(self_len),
+                ) == 0
+            }
+    }
+}
+
+impl<'a> crate::fmt::Debug for DevicePathNode<'a> {
+    fn fmt(&self, f: &mut crate::fmt::Formatter<'_>) -> crate::fmt::Result {
+        let p = device_node_to_text(self.protocol).unwrap();
+        p.fmt(f)
+    }
+}
+
 pub(crate) struct OwnedProtocol<T> {
     guid: r_efi::efi::Guid,
     handle: NonNull<crate::ffi::c_void>,