[RFC PATCH v2 03/30] samples: rust: add initial ro file system sample

[Wedson Almeida Filho <wedsonaf@gmail.com>]

From: Wedson Almeida Filho <walmeida@microsoft.com>

Introduce a basic sample that for now only registers the file system and
doesn't really provide any functionality beyond having it listed in
`/proc/filesystems`. New functionality will be added to the sample in
subsequent patches as their abstractions are introduced.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
 samples/rust/Kconfig      | 10 ++++++++++
 samples/rust/Makefile     |  1 +
 samples/rust/rust_rofs.rs | 19 +++++++++++++++++++
 3 files changed, 30 insertions(+)
 create mode 100644 samples/rust/rust_rofs.rs

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 59f44a8b6958..2f26c5c52813 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -41,6 +41,16 @@ config SAMPLE_RUST_PRINT
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_ROFS
+	tristate "Read-only file system"
+	help
+	  This option builds the Rust read-only file system sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_rofs.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 791fc18180e9..df1e4341ae95 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -3,5 +3,6 @@
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_INPLACE)		+= rust_inplace.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
+obj-$(CONFIG_SAMPLE_RUST_ROFS)			+= rust_rofs.o
 
 subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs
diff --git a/samples/rust/rust_rofs.rs b/samples/rust/rust_rofs.rs
new file mode 100644
index 000000000000..d465b107a07d
--- /dev/null
+++ b/samples/rust/rust_rofs.rs
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust read-only file system sample.
+
+use kernel::prelude::*;
+use kernel::{c_str, fs};
+
+kernel::module_fs! {
+    type: RoFs,
+    name: "rust_rofs",
+    author: "Rust for Linux Contributors",
+    description: "Rust read-only file system sample",
+    license: "GPL",
+}
+
+struct RoFs;
+impl fs::FileSystem for RoFs {
+    const NAME: &'static CStr = c_str!("rust_rofs");
+}
-- 
2.34.1