app_loader: add uninstall functionality #4528

viswajith-g · 2025-07-25T20:59:52Z

Pull Request Overview

This pr introduces an uninstall(ShortId, app_version) function to the dynamic process loader.

The uninstall operation supports two cases:

The application is currently enabled (i.e., running as a process)
The application is installed but disabled (i.e., present in storage, but not loaded as a process)

The uninstall procedure involves three steps:

Locate the Binary
- Scan the storage to find a binary that matches the ShortId and app_version values
Terminate if Running
If the binary corresponds to a currently running process:
- Terminate the process
- Remove it from the process array

If the binary is not enabled, this step does nothing.

Remove and Pad
- Erase the binary from flash, and write a padding app in its place

Testing Strategy

This pull request was tested by running a blink app on an nRF52840dk and then using a helper app to uninstall it.

TODO or Help Wanted

N/A

Documentation Updated

Updated the relevant files in /docs, or no updates are required.

Formatting

Ran make prepush.

viswajith-g · 2025-07-25T21:09:06Z

I implemented a helper that iterates over loaded processes to detect and remove any matching instance in the kernel. I did not want to the async loader to track these additional states

bradjc · 2025-07-28T17:39:33Z

capsules/extra/src/app_loader.rs

+                kernel_data
+                    .schedule_upcall(upcall::UNINSTALL_DONE, (into_statuscode(result), 0, 0))
+                    .ok();


Suggested change

kernel_data

.schedule_upcall(upcall::UNINSTALL_DONE, (into_statuscode(result), 0, 0))

.ok();

let _ = kernel_data

.schedule_upcall(upcall::UNINSTALL_DONE, (into_statuscode(result), 0, 0));

bradjc · 2025-07-28T17:41:11Z

kernel/src/dynamic_binary_storage.rs

+    /// Call to uninstall an app with given ShortId and app version.
+    fn uninstall(&self, short_id: usize, app_version: usize) -> Result<(), ErrorCode>;


Why isn't this short_id: ShortId using the actual type?

We don't have "install" so maybe we shouldn't have "uninstall" in this trait. What about "remove" or "erase"? I think the arguments make sense because it is the only general way to identify a unique app binary.

The comment should be more specific about what this operation has to do exactly.

because I wanted to keep all this within the dynamic_binary_storage capsule. It can be changed to app_loader.

Hm. Essentially we aim to terminate the process and then erase. Which is two operations. Hence, the name uninstall for this function.

But why would the trait responsible for storing an app also be expected to track the state of the app, possibly terminate, and do whatever else is required? I would expect the implementor to just have to worry about how apps are stored.

bradjc · 2025-07-28T17:51:02Z

kernel/src/kernel.rs

+    /// Terminate a process if it exists, and remove it from ProcessArray.
+    pub(crate) fn reclaim_app_memory(&self, shortid: process::ShortId) {
+        for slot in self.processes.iter() {
+            if let Some(process) = slot.get() {
+                if process.short_app_id() == shortid {
+                    process.terminate(None);
+                    slot.proc.set(None);
+                    break;
+                }
+            }
+        }
+    }


I agree this reclaims the slot in the processes array, but the app memory is still effectively lost isn't it?

Yeah, the memory is lost because of how the SequentialProcessLoadingMachine is implemented. We need to scan RAM for new memory availability similar to scan_flash_for_binaries().

Ok, I just pushed a commit which fixes this. It is very inelegant, but it scans for memory regions just before process creation and passes the slice of app_memory much like we do with flash.

In the iteration before this change, the memory region shrinks, so uninstalling the app and reinstalling it still placed the new memory region at 0x20016000.

bradjc · 2025-07-28T17:53:10Z

kernel/src/process_binary.rs

+
+    /// Credential to vaildate if the app needs to be loaded
+    pub valid_app: bool,


Instead of duplicating this information, we can just call self.header.enabled() if we need to know this

Yeah, makes sense

bradjc · 2025-07-28T17:54:35Z

kernel/src/process_binary.rs

-        // If this is an app but it isn't enabled, then we can return an error.
-        if !tbf_header.enabled() {
-            if config::CONFIG.debug_load_processes {
-                debug!(
-                    "Process not enabled flash={:#010X}-{:#010X} process={:?}",
-                    app_flash.as_ptr() as usize,
-                    app_flash.as_ptr() as usize + app_flash.len() - 1,
-                    tbf_header.get_package_name().unwrap_or("(no name)")
-                );
-            }
-            return Err(ProcessBinaryError::NotEnabledProcess);
-        }


Why is this no longer an error?

Because if this errors out, we don't get the process binary object to compute the ShortId from.

I think that's fine, but the error variant needs to be removed entirely.

bradjc · 2025-07-29T15:33:29Z

I think that adding a dynamic RAM slice approach needs to be its own PR. There is a lot going on in that change and it really needs independent scrutiny. My initial thought is I think the size of the memory region has to remain in ProcessStandard::create(). The caller can pass in multiple candidate slices, but we won't know the actual size until ProcessStandard::create() is able to compute it. Although even that is tricky, because the MPU has to be able to protect the region. This might require more thought.

viswajith-g added 4 commits July 25, 2025 16:33

add uninstall fns to capsules

2632ff3

working uninstall() first pass

91f1e13

add suppor to uninstall disabled apps

c8c77d0

app_loader: uninstall() now requires app_version along with short id

b47b177

github-actions bot added the kernel label Jul 25, 2025

add function comments

cc4989d

github-actions bot assigned alevy Jul 26, 2025

viswajith-g mentioned this pull request Jul 28, 2025

Uninstall previous version when installing an app #4530

Open

2 tasks

bradjc reviewed Jul 28, 2025

View reviewed changes

memory is now reclaimed and redistributed

db76ecb

github-actions bot added the component label Jul 29, 2025

bradjc changed the title ~~app_loader: add uninstall functionailty~~ app_loader: add uninstall functionality Jul 29, 2025

compute two best ram regions: first pass

9b44bae

		/// Call to uninstall an app with given ShortId and app version.
		fn uninstall(&self, short_id: usize, app_version: usize) -> Result<(), ErrorCode>;


		/// Credential to vaildate if the app needs to be loaded
		pub valid_app: bool,

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app_loader: add uninstall functionality #4528

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viswajith-g commented Jul 25, 2025

Pull Request Overview

Testing Strategy

TODO or Help Wanted

Documentation Updated

Formatting

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viswajith-g commented Jul 25, 2025

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bradjc commented Jul 29, 2025

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