default-uart-client: a fallback io client (mostly) for autostart

Adds a kata-io-compatible client that returns data from a slice and
sends writes to the kernel (if possible) or discards them.  This will
be used for running cli scripts and for platforms that do not have a
uart device/driver.

Change-Id: I84facebf16eb9b6692e872e930db027998dd160f
GitOrigin-RevId: 11a3502fb2f8716f9d1a204519b5e93162274590

apps/system/components/DebugConsole/Cargo.toml

@@ -15,6 +15,7 @@
 [workspace]
 
 members = [
+    "default-uart-client",
     "kata-debug-console",
     "kata-io",
     "kata-line-reader",

apps/system/components/DebugConsole/default-uart-client/Cargo.toml

@@ -0,0 +1,31 @@
+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+[package]
+name = "default-uart-client"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+
+[build-dependencies]
+sel4-config = { path = "../../kata-os-common/src/sel4-config" }
+
+[features]
+default = []
+CONFIG_PRINTING = []
+
+[dependencies]
+core2 = { version = "0.3", default-features = false }
+kata-io = { path = "../kata-io" }
+sel4-sys = { path = "../../kata-os-common/src/sel4-sys", default-features = false }

apps/system/components/DebugConsole/default-uart-client/build.rs

@@ -0,0 +1,33 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::env;
+
+fn main() {
+    // If SEL4_OUT_DIR is not set we expect the kernel build at a fixed
+    // location relative to the ROOTDIR env variable.
+    println!("SEL4_OUT_DIR {:?}", env::var("SEL4_OUT_DIR"));
+    let sel4_out_dir = env::var("SEL4_OUT_DIR")
+        .unwrap_or_else(|_| format!("{}/out/kata/kernel", env::var("ROOTDIR").unwrap()));
+    println!("sel4_out_dir {}", sel4_out_dir);
+
+    // Dredge seL4 kernel config for settings we need as features to generate
+    // correct code: e.g. CONFIG_KERNEL_MCS enables MCS support which changes
+    // the system call numbering.
+    let features = sel4_config::get_sel4_features(&sel4_out_dir);
+    println!("features={:?}", features);
+    for feature in features {
+        println!("cargo:rustc-cfg=feature=\"{}\"", feature);
+    }
+}

apps/system/components/DebugConsole/default-uart-client/src/lib.rs

@@ -0,0 +1,61 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![no_std]
+
+use core2::io::{Cursor, Read};
+use kata_io as io;
+
+/// Rx io trait that returns data from a byte string.
+pub struct Rx<'a> {
+    data: Cursor<&'a [u8]>,
+}
+impl<'a> Rx<'a> {
+    pub fn new(data: &'a [u8]) -> Self {
+        Self {
+            data: Cursor::new(data),
+        }
+    }
+}
+impl<'a> io::Read for Rx<'a> {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.data.read(buf).map_err(|_| io::Error)
+    }
+}
+
+/// Tx io trait that uses the kernel if console output is
+/// is supported, otherwise discards all writes.
+pub struct Tx {}
+impl Tx {
+    pub fn new() -> Self { Self {} }
+}
+impl Default for Tx {
+    fn default() -> Self { Self::new() }
+}
+
+impl io::Write for Tx {
+    #[cfg(not(feature = "CONFIG_PRINTING"))]
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len() as usize) }
+    #[cfg(feature = "CONFIG_PRINTING")]
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        for &b in buf {
+            unsafe {
+                sel4_sys::seL4_DebugPutChar(b);
+            }
+        }
+        Ok(buf.len() as usize)
+    }
+
+    fn flush(&mut self) -> io::Result<()> { Ok(()) }
+}