[PATCH] fault-inject: rust: add a Rust API for fault-injection

[Andreas Hindborg <a.hindborg@kernel.org>]

Add a way for Rust code to create fault-injection control points. The
control points can be attached to a configfs tree as default groups and
controlled from user space. On the kernel side, provide a `should_fail`
method to query if an operation should fail.

Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
This patch is a dependency for the rust null block driver fault
injection feature.
---
 rust/bindings/bindings_helper.h |  1 +
 rust/kernel/fault_injection.rs  | 88 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  2 +
 3 files changed, 91 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index a067038b4b422..87cbaf69d330e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -54,6 +54,7 @@
 #include <linux/errname.h>
 #include <linux/ethtool.h>
 #include <linux/fdtable.h>
+#include <linux/fault-inject.h>
 #include <linux/file.h>
 #include <linux/firmware.h>
 #include <linux/interrupt.h>
diff --git a/rust/kernel/fault_injection.rs b/rust/kernel/fault_injection.rs
new file mode 100644
index 0000000000000..e9afa3ca6cf31
--- /dev/null
+++ b/rust/kernel/fault_injection.rs
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Fault injection capabilities infrastructure.
+//!
+//! This module provides a Rust API for the kernel fault injection framework.
+//! Fault injection allows simulation of failures in kernel code paths to test
+//! error handling.
+//!
+//! [`FaultConfig`] represents a fault injection control point that can be:
+//!
+//! - Attached to a configfs tree as a default group, allowing userspace control
+//!   of fault injection parameters.
+//! - Queried via [`FaultConfig::should_fail`] to determine if an operation
+//!   should be simulated as failing.
+//!
+//! Please see the [fault injection documentation] for details on configuring
+//! and using fault injection from userspace.
+//!
+//! C header: [`include/linux/fault-inject.h`](srctree/include/linux/fault-inject.h)
+//!
+//! [fault injection documentation]: srctree/Documentation/fault-injection/fault-injection.rst
+
+use crate::{prelude::*, types::Opaque};
+
+/// A fault injection control point.
+///
+/// This type wraps a `struct fault_config` from the C fault injection
+/// framework. It provides a way to create controllable fault injection points
+/// that can be configured via configfs.
+///
+/// When attached to a configfs subsystem as a default group, userspace can
+/// configure fault injection parameters through the configfs interface. The
+/// kernel code can then query [`FaultConfig::should_fail`] to determine
+/// whether to simulate a failure.
+///
+/// # Invariants
+///
+/// - `self.inner` is always a valid `struct fault_config`.
+#[pin_data]
+pub struct FaultConfig {
+    #[pin]
+    inner: Opaque<bindings::fault_config>,
+}
+
+impl FaultConfig {
+    /// Create a new [`FaultConfig`].
+    ///
+    /// If attached to a configfs group, this [`FaultConfig`] will appear as a directory named
+    /// `name`.
+    pub fn new(name: &CStr) -> impl PinInit<Self> + use<'_> {
+        pin_init!(Self {
+            // INVARIANT: `self.inner` is initialized in ffi_init.
+            inner <- Opaque::zeroed().chain(|inner| {
+                let ptr = inner.get();
+                // SAFETY: `ptr` points to a zeroed allocation and the second argument is null
+                // terminated string.
+                unsafe { bindings::fault_config_init( ptr, name.as_ptr().cast()) };
+                Ok(())
+            }),
+        })
+    }
+}
+
+impl kernel::configfs::CDefaultGroup for FaultConfig {
+    fn group_ptr(&self) -> *mut bindings::config_group {
+        // SAFETY: By type invariant, `self.inner` is valid.
+        unsafe { &raw mut (*self.inner.get()).group }
+    }
+}
+
+impl FaultConfig {
+    /// Query for failure.
+    ///
+    /// Returns true if the operation should fail.
+    pub fn should_fail(&self, size: isize) -> bool {
+        // SAFETY: By type invariant, self is always valid.
+        let attr = unsafe { &raw const (*self.inner.get()).attr };
+
+        // SAFETY: By type invariant, self is always valid.
+        unsafe { bindings::should_fail(attr.cast_mut(), size) }
+    }
+}
+
+// SAFETY: FaultConfig can be used from any task.
+unsafe impl Send for FaultConfig {}
+
+// SAFETY: FaultConfig applies internal synchronization.
+unsafe impl Sync for FaultConfig {}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index f812cf1200428..1b8f1a216a268 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -92,6 +92,8 @@
 #[cfg(CONFIG_DRM = "y")]
 pub mod drm;
 pub mod error;
+#[cfg(all(CONFIG_FAULT_INJECTION, CONFIG_FAULT_INJECTION_CONFIGFS))]
+pub mod fault_injection;
 pub mod faux;
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;

---
base-commit: e9ec05addd1a067fc7cb218f20ecdc1b1b0898c0
change-id: 20260215-rust-fault-inject-bc62f1083502
prerequisite-change-id: 20260215-configfs-c-default-groups-bdb0a44633a6:v1
prerequisite-patch-id: 5c82dc0deb0768531d2cdb24ac5e92857c9e76a7

Best regards,
-- 
Andreas Hindborg <a.hindborg@kernel.org>