Put shared buffer into UnsafeCell

Author: torfmaster

core/src/shared_memory.rs

@@ -1,36 +1,45 @@
 use crate::syscalls;
+use core::cell::UnsafeCell;
 use core::ptr;
 
 #[must_use = "Shared memory risks being dropped too early. Drop it manually."]
-pub struct SharedMemory<'a> {
+pub struct SharedMemory<T> {
     driver_number: usize,
     allow_number: usize,
-    buffer_to_share: &'a mut [u8],
+    buffer_to_share: UnsafeCell<T>,
 }
 
-impl<'a> SharedMemory<'a> {
-    pub fn new(
-        driver_number: usize,
-        allow_number: usize,
-        buffer_to_share: &'a mut [u8],
-    ) -> SharedMemory<'a> {
+impl<T> SharedMemory<T>
+where
+    T: AsMut<[u8]>,
+{
+    pub fn new(driver_number: usize, allow_number: usize, buffer_to_share: T) -> SharedMemory<T> {
         SharedMemory {
             driver_number,
             allow_number,
-            buffer_to_share,
+            buffer_to_share: UnsafeCell::new(buffer_to_share),
         }
     }
 
-    pub fn read_bytes<T: AsMut<[u8]>>(&self, mut destination: T) {
-        safe_copy(self.buffer_to_share, destination.as_mut());
+    pub fn read_bytes<D: AsMut<[u8]>>(&self, mut destination: D) {
+        let buf = unsafe { (*self.buffer_to_share.get()).as_mut() };
+        safe_copy(buf, destination.as_mut());
     }
 
-    pub fn write_bytes<T: AsRef<[u8]>>(&mut self, source: T) {
-        safe_copy(source.as_ref(), self.buffer_to_share);
+    pub fn write_bytes<S: AsRef<[u8]>>(&mut self, source: S) {
+        let buf = unsafe { (*self.buffer_to_share.get()).as_mut() };
+        safe_copy(source.as_ref(), buf);
+    }
+
+    pub(crate) unsafe fn operate_on_mut_ptr<R: Sized, F: FnOnce(*mut u8) -> R>(
+        &self,
+        func: F,
+    ) -> R {
+        func((*self.buffer_to_share.get()).as_mut().as_mut_ptr())
     }
 }
 
-impl<'a> Drop for SharedMemory<'a> {
+impl<T> Drop for SharedMemory<T> {
     fn drop(&mut self) {
         unsafe {
             syscalls::raw::allow(self.driver_number, self.allow_number, ptr::null_mut(), 0);

core/src/syscalls/mod.rs

@@ -112,26 +112,20 @@ pub fn command1_insecure(
     }
 }
 
-pub fn allow(
+pub fn allow<T: AsMut<[u8]>>(
     driver_number: usize,
     allow_number: usize,
-    buffer_to_share: &mut [u8],
-) -> Result<SharedMemory, AllowError> {
-    let len = buffer_to_share.len();
+    mut buffer_to_share: T,
+) -> Result<SharedMemory<T>, AllowError> {
+    let len = buffer_to_share.as_mut().len();
+    let shared_memory = SharedMemory::new(driver_number, allow_number, buffer_to_share);
     let return_code = unsafe {
-        raw::allow(
-            driver_number,
-            allow_number,
-            buffer_to_share.as_mut_ptr(),
-            len,
-        )
+        shared_memory
+            .operate_on_mut_ptr(|pointer| raw::allow(driver_number, allow_number, pointer, len))
     };
+
     if return_code == 0 {
-        Ok(SharedMemory::new(
-            driver_number,
-            allow_number,
-            buffer_to_share,
-        ))
+        Ok(shared_memory)
     } else {
         Err(AllowError {
             driver_number,

examples-features/ble_scanning.rs

@@ -23,7 +23,7 @@ async fn main() -> TockResult<()> {
 
     loop {
         let value = ble_scanning_driver_scanning.stream_values().await;
-        ble_parser::find(&value, simple_ble::gap_data::SERVICE_DATA as u8)
+        ble_parser::find(value.as_ref(), simple_ble::gap_data::SERVICE_DATA as u8)
             .and_then(|service_data| ble_parser::extract_for_service([91, 79], service_data))
             .and_then(|payload| corepack::from_bytes::<LedCommand>(&payload).ok())
             .and_then(|msg| leds_driver.get(msg.nr as usize).ok())

examples-features/simple_ble.rs

@@ -27,7 +27,7 @@ async fn main() -> TockResult<()> {
 
     let payload = corepack::to_bytes(LedCommand { nr: 2, st: true }).unwrap();
 
-    let mut buffer = BleAdvertisingDriver::create_advertising_buffer();
+    let buffer = BleAdvertisingDriver::create_advertising_buffer();
     let mut gap_payload = BlePayload::default();
 
     gap_payload
@@ -44,7 +44,7 @@ async fn main() -> TockResult<()> {
 
     gap_payload.add_service_payload([91, 79], &payload).unwrap();
 
-    let _handle = ble_advertising_driver.initialize(100, &gap_payload, &mut buffer);
+    let _handle = ble_advertising_driver.initialize(100, &gap_payload, buffer);
 
     loop {
         led.on()?;

examples/adc_buffer.rs

@@ -13,10 +13,10 @@ async fn main() -> TockResult<()> {
     let adc_driver = drivers.adc.init_driver()?;
     let mut console = drivers.console.create_console();
 
-    let mut adc_buffer = AdcBuffer::default();
+    let adc_buffer = AdcBuffer::default();
     let mut temp_buffer = [0; libtock::adc::BUFFER_SIZE];
 
-    let adc_buffer = adc_driver.init_buffer(&mut adc_buffer)?;
+    let adc_buffer = adc_driver.init_buffer(adc_buffer)?;
 
     let mut callback = |_, _| {
         adc_buffer.read_bytes(&mut temp_buffer[..]);

src/adc.rs

@@ -45,6 +45,12 @@ pub struct AdcBuffer {
     buffer: [u8; BUFFER_SIZE],
 }
 
+impl AsMut<[u8]> for AdcBuffer {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.buffer
+    }
+}
+
 impl Default for AdcBuffer {
     fn default() -> Self {
         AdcBuffer {
@@ -67,13 +73,12 @@ impl<CB: FnMut(usize, usize)> Consumer<CB> for AdcEventConsumer {
 }
 
 impl<'a> Adc<'a> {
-    pub fn init_buffer(&self, buffer: &'a mut AdcBuffer) -> TockResult<SharedMemory> {
-        syscalls::allow(DRIVER_NUMBER, allow_nr::BUFFER, &mut buffer.buffer).map_err(Into::into)
+    pub fn init_buffer(&self, buffer: AdcBuffer) -> TockResult<SharedMemory<AdcBuffer>> {
+        syscalls::allow(DRIVER_NUMBER, allow_nr::BUFFER, buffer).map_err(Into::into)
     }
 
-    pub fn init_alt_buffer(&self, alt_buffer: &'a mut AdcBuffer) -> TockResult<SharedMemory> {
-        syscalls::allow(DRIVER_NUMBER, allow_nr::BUFFER_ALT, &mut alt_buffer.buffer)
-            .map_err(Into::into)
+    pub fn init_alt_buffer(&self, alt_buffer: AdcBuffer) -> TockResult<SharedMemory<AdcBuffer>> {
+        syscalls::allow(DRIVER_NUMBER, allow_nr::BUFFER_ALT, alt_buffer).map_err(Into::into)
     }
 
     /// Return the number of available channels

src/simple_ble.rs

@@ -53,16 +53,24 @@ impl BleAdvertisingDriverFactory {
 #[non_exhaustive]
 pub struct BleAdvertisingDriver;
 
+pub struct BleAdvertisingBuffer([u8; BUFFER_SIZE_ADVERTISE]);
+
+impl AsMut<[u8]> for BleAdvertisingBuffer {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
 impl BleAdvertisingDriver {
-    pub fn create_advertising_buffer() -> [u8; BUFFER_SIZE_ADVERTISE] {
-        [0; BUFFER_SIZE_ADVERTISE]
+    pub fn create_advertising_buffer() -> BleAdvertisingBuffer {
+        BleAdvertisingBuffer([0; BUFFER_SIZE_ADVERTISE])
     }
     pub fn initialize<'a>(
         &'a mut self,
         interval: usize,
         service_payload: &BlePayload,
-        advertising_buffer: &'a mut [u8; BUFFER_SIZE_ADVERTISE],
-    ) -> TockResult<SharedMemory<'a>> {
+        advertising_buffer: BleAdvertisingBuffer,
+    ) -> TockResult<SharedMemory<BleAdvertisingBuffer>> {
         let mut shared_memory = syscalls::allow(
             DRIVER_NUMBER,
             allow_nr::ALLOW_ADVERTISMENT_BUFFER,
@@ -86,12 +94,19 @@ impl BleAdvertisingDriver {
 
 struct BleCallback<'a> {
     read_value: &'a Cell<Option<ScanBuffer>>,
-    shared_buffer: SharedMemory<'a>,
+    shared_buffer: SharedMemory<ScanBuffer>,
 }
 
-pub(crate) type ScanBuffer = [u8; BUFFER_SIZE_SCAN];
+#[derive(Clone, Copy)]
+pub struct ScanBuffer([u8; BUFFER_SIZE_SCAN]);
+
+impl AsRef<[u8]> for ScanBuffer {
+    fn as_ref(&self) -> &[u8] {
+        &self.0
+    }
+}
 
-const EMPTY_SCAN_BUFFER: ScanBuffer = [0; BUFFER_SIZE_SCAN];
+const EMPTY_SCAN_BUFFER: ScanBuffer = ScanBuffer([0; BUFFER_SIZE_SCAN]);
 
 #[non_exhaustive]
 pub struct BleScanningDriverFactory;
@@ -130,13 +145,19 @@ pub struct BleScanningDriver {
     read_value: Cell<Option<ScanBuffer>>,
 }
 
+impl AsMut<[u8]> for ScanBuffer {
+    fn as_mut(&mut self) -> &mut [u8] {
+        &mut self.0
+    }
+}
+
 impl BleScanningDriver {
     /// Prepare Ble Scanning Driver to share memory with the ble capsule
     pub fn share_memory(&mut self) -> TockResult<BleScanningDriverShared> {
-        let shared_buffer: SharedMemory = syscalls::allow(
+        let shared_buffer = syscalls::allow(
             DRIVER_NUMBER,
             allow_nr::ALLOW_SCAN_BUFFER,
-            &mut self.shared_buffer,
+            self.shared_buffer,
         )
         .map_err(Into::<TockError>::into)?;
         Ok(BleScanningDriverShared {
@@ -195,7 +216,7 @@ impl<'a> Consumer<Self> for BleCallback<'a> {
     fn consume(callback: &mut Self, _: usize, _: usize, _: usize) {
         let mut temporary_buffer: ScanBuffer = EMPTY_SCAN_BUFFER;
 
-        callback.shared_buffer.read_bytes(&mut temporary_buffer[..]);
+        callback.shared_buffer.read_bytes(temporary_buffer.as_mut());
         callback.read_value.set(Some(temporary_buffer));
     }
 }