[PATCH v3 2/6] rust: error: Add Error::to_ptr()

[Asahi Lina]

This is the Rust equivalent to ERR_PTR(), for use in C callbacks.
Marked as #[allow(dead_code)] for now, since it does not have any
consumers yet.

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx>
Signed-off-by: Asahi Lina <lina@xxxxxxxxxxxxx>
---
 rust/helpers.c       | 7 +++++++
 rust/kernel/error.rs | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/rust/helpers.c b/rust/helpers.c
index 09a4d93f9d62..89f4cd1e0df3 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -20,6 +20,7 @@
 
 #include <linux/bug.h>
 #include <linux/build_bug.h>
+#include <linux/err.h>
 #include <linux/refcount.h>
 
 __noreturn void rust_helper_BUG(void)
@@ -46,6 +47,12 @@ bool rust_helper_refcount_dec_and_test(refcount_t *r)
 }
 EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test);
 
+__force void *rust_helper_ERR_PTR(long err)
+{
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(rust_helper_ERR_PTR);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 35894fa35efe..154d0ca6e2dc 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -76,6 +76,13 @@ impl Error {
     pub fn to_errno(self) -> core::ffi::c_int {
         self.0
     }
+
+    /// Returns the error encoded as a pointer.
+    #[allow(dead_code)]
+    pub(crate) fn to_ptr<T>(self) -> *mut T {
+        // SAFETY: self.0 is a valid error due to its invariant.
+        unsafe { bindings::ERR_PTR(self.0.into()) as *mut _ }
+    }
 }
 
 impl From<AllocError> for Error {

-- 
2.40.0