♻️ ReadOnlyDevices don't track previous values

The reason for the previous value was so, when restarting DrMem,
devices could be set back to their previous setting. Read-only devices
get their value from querying their hardware. You don't restore a
read-only device.

drmem-api/src/driver/mod.rs

@@ -42,8 +42,7 @@ pub enum Request {
         dev_name: device::Name,
         dev_units: Option<String>,
         max_history: Option<usize>,
-        rpy_chan:
-            oneshot::Sender<Result<(ReportReading, Option<device::Value>)>>,
+        rpy_chan: oneshot::Sender<Result<ReportReading>>,
     },
 
     /// Registers a writable device with core.
@@ -135,12 +134,7 @@ impl RequestChan {
 
         if result.is_ok() {
             if let Ok(v) = rx.await {
-                return v.map(|(rr, prev)| {
-                    ReadOnlyDevice::new(
-                        rr,
-                        prev.and_then(|v| T::try_from(v).ok()),
-                    )
-                });
+                return v.map(|rr| ReadOnlyDevice::new(rr));
             }
         }
 

drmem-api/src/driver/ro_device.rs

@@ -1,5 +1,6 @@
 use crate::device;
 use std::future::Future;
+use std::marker::PhantomData;
 use std::pin::Pin;
 
 /// A function that drivers use to report updated values of a device.
@@ -14,32 +15,24 @@ pub type ReportReading = Box<
 /// acceptable.
 pub struct ReadOnlyDevice<T: Into<device::Value> + Clone> {
     report_chan: ReportReading,
-    prev_val: Option<T>,
+    phantom: PhantomData<T>,
 }
 
 impl<T> ReadOnlyDevice<T>
 where
     T: Into<device::Value> + Clone,
 {
     /// Returns a new `ReadOnlyDevice` type.
-    pub fn new(report_chan: ReportReading, prev_val: Option<T>) -> Self {
+    pub fn new(report_chan: ReportReading) -> Self {
         ReadOnlyDevice {
             report_chan,
-            prev_val,
+            phantom: PhantomData,
         }
     }
 
     /// Saves a new value, returned by the device, to the backend
     /// storage.
     pub async fn report_update(&mut self, value: T) {
-        self.prev_val = Some(value.clone());
         (self.report_chan)(value.into()).await
     }
-
-    /// Gets the last value of the device. If DrMem is built with
-    /// persistent storage, this value will be initialized with the
-    /// last value saved to storage.
-    pub fn get_last(&self) -> Option<&T> {
-        self.prev_val.as_ref()
-    }
 }

drmemd/src/backends/mod.rs

@@ -35,7 +35,7 @@ pub trait Store {
         name: &device::Name,
         units: Option<&String>,
         max_history: Option<usize>,
-    ) -> Result<(driver::ReportReading, Option<device::Value>)>;
+    ) -> Result<driver::ReportReading>;
 
     // Called when a read-write device is to be registered with the
     // back-end.

drmemd/src/backends/redis/mod.rs

@@ -926,7 +926,7 @@ impl Store for RedisStore {
         name: &device::Name,
         units: Option<&String>,
         max_history: Option<usize>,
-    ) -> Result<(ReportReading, Option<device::Value>)> {
+    ) -> Result<ReportReading> {
         let name = name.to_string();
 
         debug!("registering '{}' as read-only", &name);
@@ -936,10 +936,7 @@ impl Store for RedisStore {
 
             info!("'{}' has been successfully created", &name);
         }
-        Ok((
-            self.mk_report_func(&name, max_history),
-            self.last_value(&name).await.map(|v| v.value),
-        ))
+        Ok(self.mk_report_func(&name, max_history))
     }
 
     async fn register_read_write_device(

drmemd/src/backends/simple/mod.rs

@@ -145,7 +145,7 @@ impl Store for SimpleStore {
         name: &device::Name,
         units: Option<&String>,
         _max_history: Option<usize>,
-    ) -> Result<(ReportReading, Option<device::Value>)> {
+    ) -> Result<ReportReading> {
         // Check to see if the device name already exists.
 
         match self.0.entry((*name).clone()) {
@@ -163,7 +163,7 @@ impl Store for SimpleStore {
                 // Create and return the closure that the driver will
                 // use to report updates.
 
-                Ok((mk_report_func(di, name), None))
+                Ok(mk_report_func(di, name))
             }
 
             // The device already exists. If it was created from a
@@ -174,18 +174,8 @@ impl Store for SimpleStore {
 
                 if dev_info.owner.as_ref() == driver {
                     let func = mk_report_func(dev_info, name);
-                    let guard = dev_info.reading.lock();
 
-                    Ok((
-                        func,
-                        if let Ok(data) = guard {
-                            data.1.as_ref().map(
-                                |device::Reading { value, .. }| value.clone(),
-                            )
-                        } else {
-                            None
-                        },
-                    ))
+                    Ok(func)
                 } else {
                     Err(Error::InUse)
                 }
@@ -483,7 +473,7 @@ mod tests {
         let mut db = SimpleStore(HashMap::new());
         let name = "test:device".parse::<device::Name>().unwrap();
 
-        if let Ok((f, None)) = db
+        if let Ok(f) = db
             .register_read_only_device("test", &name, None, None)
             .await
         {
@@ -567,7 +557,7 @@ mod tests {
         let mut db = SimpleStore(HashMap::new());
         let name = "test:device".parse::<device::Name>().unwrap();
 
-        if let Ok((f, None)) = db
+        if let Ok(f) = db
             .register_read_only_device("test", &name, None, None)
             .await
         {
@@ -654,7 +644,7 @@ mod tests {
         let mut db = SimpleStore(HashMap::new());
         let name = "test:device".parse::<device::Name>().unwrap();
 
-        if let Ok((f, None)) = db
+        if let Ok(f) = db
             .register_read_only_device("test", &name, None, None)
             .await
         {
@@ -698,7 +688,7 @@ mod tests {
         let mut db = SimpleStore(HashMap::new());
         let name = "test:device".parse::<device::Name>().unwrap();
 
-        if let Ok((f, None)) = db
+        if let Ok(f) = db
             .register_read_only_device("test", &name, None, None)
             .await
         {
@@ -887,7 +877,7 @@ mod tests {
         // Register a device named "junk" and associate it with the
         // driver named "test". We don't define units for this device.
 
-        if let Ok((f, None)) = db
+        if let Ok(f) = db
             .register_read_only_device("test", &name, None, None)
             .await
         {
@@ -922,7 +912,7 @@ mod tests {
             // Assert that re-registering this device with the same
             // driver name is successful.
 
-            if let Ok((f, Some(device::Value::Int(1)))) = db
+            if let Ok(f) = db
                 .register_read_only_device("test", &name, None, None)
                 .await
             {