Add linux_rustix opt-in backend

.github/workflows/nopanic.yaml

@@ -40,6 +40,13 @@ jobs:
       - name: Check (linux_android.rs)
         run: ret=$(grep panic target/release/libgetrandom_wrapper.so; echo $?); [ $ret -eq 1 ]
 
+      - name: Build (linux_rustix.rs)
+        env:
+          RUSTFLAGS: -Dwarnings --cfg getrandom_backend="linux_rustix"
+        run: cargo build --release
+      - name: Check (linux_rustix.rs)
+        run: ret=$(grep panic target/release/libgetrandom_wrapper.so; echo $?); [ $ret -eq 1 ]
+
       - name: Build (rdrand.rs)
         env:
           RUSTFLAGS: -Dwarnings --cfg getrandom_backend="rdrand"

.github/workflows/tests.yml

@@ -71,6 +71,9 @@ jobs:
       - env:
           RUSTFLAGS: -Dwarnings --cfg getrandom_backend="linux_getrandom"
         run: cargo test ${{ matrix.cargo_test_opts }} --target=${{ matrix.target }} --features=std
+      - env:
+          RUSTFLAGS: -Dwarnings --cfg getrandom_backend="linux_rustix"
+        run: cargo test ${{ matrix.cargo_test_opts }} --target=${{ matrix.target }} --features=std
       - env:
           RUSTFLAGS: -Dwarnings --cfg getrandom_test_linux_fallback
         run: cargo test --features=std

.github/workflows/workspace.yml

@@ -53,6 +53,10 @@ jobs:
       env:
         RUSTFLAGS: -Dwarnings --cfg getrandom_backend="linux_getrandom"
       run: cargo clippy --target x86_64-unknown-linux-gnu
+    - name: Linux (linux_rustix.rs)
+      env:
+        RUSTFLAGS: -Dwarnings --cfg getrandom_backend="linux_rustix"
+      run: cargo clippy --target x86_64-unknown-linux-gnu
     - name: Linux (linux_android_with_fallback.rs)
       run: cargo clippy --target x86_64-unknown-linux-gnu
     - name: NetBSD (netbsd.rs)

Cargo.toml

@@ -18,9 +18,12 @@ cfg-if = "1"
 compiler_builtins = { version = "0.1", optional = true }
 core = { version = "1.0", optional = true, package = "rustc-std-workspace-core" }
 
-[target.'cfg(unix)'.dependencies]
+[target.'cfg(all(unix, not(getrandom_backend = "linux_rustix")))'.dependencies]
 libc = { version = "0.2.154", default-features = false }
 
+[target.'cfg(all(getrandom_backend = "linux_rustix", any(target_os = "linux", target_os = "android")))'.dependencies]
+rustix = { version = "0.38", default-features = false, features = ["rand"] }
+
 [target.'cfg(all(target_arch = "wasm32", target_os = "wasi", target_env = "p2"))'.dependencies]
 wasi = { version = "0.13", default-features = false }
 
@@ -42,7 +45,7 @@ rustc-dep-of-std = ["compiler_builtins", "core"]
 [lints.rust.unexpected_cfgs]
 level = "warn"
 check-cfg = [
-  'cfg(getrandom_backend, values("custom", "rdrand", "rndr", "linux_getrandom", "wasm_js", "esp_idf"))',
+  'cfg(getrandom_backend, values("custom", "rdrand", "rndr", "linux_getrandom", "linux_rustix", "wasm_js", "esp_idf"))',
   'cfg(getrandom_browser_test)',
   'cfg(getrandom_test_linux_fallback)',
 ]

src/lib.rs

@@ -41,6 +41,7 @@
 //! | Backend name      | Target               | Target Triple        | Implementation
 //! | ----------------- | -------------------- | -------------------- | --------------
 //! | `linux_getrandom` | Linux, Android       | `*‑linux‑*`          | [`getrandom`][1] system call (without `/dev/urandom` fallback). Bumps minimum supported Linux kernel version to 3.17 and Android API level to 23 (Marshmallow).
+//! | `linux_rustix`    | Linux, Android       | `*‑linux‑*`          | [`getrandom`][1] system call using the [`rustix`] crate
 //! | `rdrand`          | x86, x86-64          | `x86_64-*`, `i686-*` | [`RDRAND`] instruction
 //! | `rndr`            | AArch64              | `aarch64-*`          | [`RNDR`] register
 //! | `esp_idf`         | ESP-IDF              | `*‑espidf`           | [`esp_fill_random`]. WARNING: can return low quality entropy without proper hardware configuration!
@@ -243,6 +244,7 @@
 //! [platform-support]: https://doc.rust-lang.org/stable/rustc/platform-support.html
 //! [WASI]: https://github.com/CraneStation/wasi
 //! [Emscripten]: https://www.hellorust.com/setup/emscripten/
+//! [`rustix`]: https://docs.rs/rustix
 
 #![doc(
     html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
@@ -295,6 +297,8 @@ cfg_if! {
     } else if #[cfg(getrandom_backend = "linux_getrandom")] {
         mod util_libc;
         #[path = "linux_android.rs"] mod imp;
+    } else if #[cfg(getrandom_backend = "linux_rustix")] {
+        #[path = "linux_rustix.rs"] mod imp;
     } else if #[cfg(getrandom_backend = "rdrand")] {
         mod lazy;
         #[path = "rdrand.rs"] mod imp;

src/linux_rustix.rs

@@ -0,0 +1,30 @@
+//! Implementation for Linux / Android without `/dev/urandom` fallback
+use crate::{Error, MaybeUninit};
+use rustix::rand::{getrandom_uninit, GetRandomFlags};
+
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+compile_error!("`linux_rustix` backend can be enabled only for Linux/Android targets!");
+
+pub fn getrandom_inner(mut dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
+    loop {
+        let res = getrandom_uninit(dest, GetRandomFlags::empty()).map(|(res, _)| res.len());
+        match res {
+            Ok(0) => return Err(Error::UNEXPECTED),
+            Ok(res_len) => {
+                dest = dest.get_mut(res_len..).ok_or(Error::UNEXPECTED)?;
+                if !dest.is_empty() {
+                    return Ok(());
+                }
+            }
+            Err(rustix::io::Errno::INTR) => continue,
+            Err(err) => {
+                let code = err
+                    .raw_os_error()
+                    .wrapping_neg()
+                    .try_into()
+                    .expect("Errno uses u16 internally");
+                return Err(Error::from_os_error(code));
+            }
+        }
+    }
+}