add UrandomDev (#2)

Author: SiyuanSun0736

axfs_devfs/src/lib.rs

@@ -8,13 +8,15 @@ extern crate alloc;
 
 mod dir;
 mod null;
+mod urandom;
 mod zero;
 
 #[cfg(test)]
 mod tests;
 
 pub use self::dir::DirNode;
 pub use self::null::NullDev;
+pub use self::urandom::UrandomDev;
 pub use self::zero::ZeroDev;
 
 use alloc::sync::Arc;

axfs_devfs/src/urandom.rs

@@ -0,0 +1,74 @@
+use axfs_vfs::{VfsNodeAttr, VfsNodeOps, VfsNodePerm, VfsNodeType, VfsResult};
+use core::sync::atomic::{AtomicU64, Ordering};
+
+/// A urandom device behaves like `/dev/urandom`.
+///
+/// It produces random bytes when read.
+pub struct UrandomDev {
+    seed: AtomicU64,
+}
+
+impl UrandomDev {
+    /// Create a new instance of the urandom device.
+    pub const fn new(seed: u64) -> Self {
+        Self {
+            seed: AtomicU64::new(seed),
+        }
+    }
+
+    /// Create a new instance with a default seed.
+    fn new_with_default_seed() -> Self {
+        Self::new(0xa2ce_a2ce)
+    }
+
+    /// LCG pseudo-random number generator
+    fn next_u64(&self) -> u64 {
+        let new_seed = self
+            .seed
+            .load(Ordering::SeqCst)
+            .wrapping_mul(6364136223846793005)
+            + 1;
+        self.seed.store(new_seed, Ordering::SeqCst);
+        new_seed
+    }
+}
+
+impl Default for UrandomDev {
+    fn default() -> Self {
+        Self::new_with_default_seed()
+    }
+}
+
+impl VfsNodeOps for UrandomDev {
+    fn get_attr(&self) -> VfsResult<VfsNodeAttr> {
+        Ok(VfsNodeAttr::new(
+            VfsNodePerm::default_file(),
+            VfsNodeType::CharDevice,
+            0,
+            0,
+        ))
+    }
+
+    fn read_at(&self, _offset: u64, buf: &mut [u8]) -> VfsResult<usize> {
+        for chunk in buf.chunks_mut(8) {
+            let random_value = self.next_u64();
+            let bytes = random_value.to_ne_bytes();
+            for (i, byte) in chunk.iter_mut().enumerate() {
+                if i < bytes.len() {
+                    *byte = bytes[i];
+                }
+            }
+        }
+        Ok(buf.len())
+    }
+
+    fn write_at(&self, _offset: u64, buf: &[u8]) -> VfsResult<usize> {
+        Ok(buf.len())
+    }
+
+    fn truncate(&self, _size: u64) -> VfsResult {
+        Ok(())
+    }
+
+    axfs_vfs::impl_vfs_non_dir_default! {}
+}