phase 0+1: fix Rust 2024 edition compat + memory query

- unsafe extern "C" blocks (Rust 2024 requirement)
- unsafe blocks inside unsafe fn bodies
- Use cudaMemGetInfo for accurate GPU memory reporting
- Remove cc "cuda" feature (doesn't exist, built-in)
- All 12 tests pass on RTX 5090 (CC 12.0, 170 SMs, 32GB)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/xserv-cuda/Cargo.toml

@@ -4,7 +4,7 @@ version.workspace = true
 edition.workspace = true
 
 [build-dependencies]
-cc = { version = "1", features = ["cuda"] }
+cc = "1"
 
 [dev-dependencies]
 rand = "0.9"

crates/xserv-cuda/src/device.rs

@@ -7,6 +7,7 @@ pub struct DeviceInfo {
     pub index: u32,
     pub name: String,
     pub total_memory: usize,
+    pub free_memory: usize,
     pub compute_major: i32,
     pub compute_minor: i32,
     pub sm_count: i32,
@@ -15,8 +16,9 @@ pub struct DeviceInfo {
     pub max_threads_per_block: i32,
 }
 
-extern "C" {
+unsafe extern "C" {
     fn cudaDeviceGetAttribute(value: *mut i32, attr: i32, device: i32) -> i32;
+    fn cudaMemGetInfo(free: *mut usize, total: *mut usize) -> i32;
 }
 
 fn get_attr(attr: i32, device: u32) -> Result<i32> {
@@ -42,16 +44,24 @@ pub fn current_device() -> Result<u32> {
 }
 
 pub fn device_info(device: u32) -> Result<DeviceInfo> {
-    // Use cudaGetDeviceProperties only for the name (first field, always stable).
+    // Get device name from cudaGetDeviceProperties (only use the name field).
     let mut prop = unsafe { std::mem::zeroed::<ffi::CudaDeviceProp>() };
     error::check(unsafe { ffi::cudaGetDeviceProperties(&mut prop, device as i32) })?;
     let name = unsafe { CStr::from_ptr(prop.name.as_ptr()) }
         .to_string_lossy()
         .into_owned();
 
-    // Use cudaDeviceGetAttribute for everything else (layout-independent).
-    // Attribute IDs from cuda_runtime_api.h:
-    const TOTAL_GLOBAL_MEM: i32 = 0; // not available via attribute, use prop
+    // Get memory info via cudaMemGetInfo (layout-independent).
+    let prev = current_device()?;
+    set_device(device)?;
+    let mut free = 0usize;
+    let mut total = 0usize;
+    error::check(unsafe { cudaMemGetInfo(&mut free, &mut total) })?;
+    if prev != device {
+        set_device(prev)?;
+    }
+
+    // Attribute IDs from cuda_runtime_api.h
     const SHARED_MEM_PER_BLOCK: i32 = 8;
     const WARP_SIZE: i32 = 10;
     const MAX_THREADS_PER_BLOCK: i32 = 1;
@@ -62,7 +72,8 @@ pub fn device_info(device: u32) -> Result<DeviceInfo> {
     Ok(DeviceInfo {
         index: device,
         name,
-        total_memory: prop.total_global_mem,
+        total_memory: total,
+        free_memory: free,
         compute_major: get_attr(COMPUTE_MAJOR, device)?,
         compute_minor: get_attr(COMPUTE_MINOR, device)?,
         sm_count: get_attr(MULTI_PROCESSOR_COUNT, device)?,

crates/xserv-cuda/src/ffi.rs

@@ -30,7 +30,7 @@ pub struct CudaDeviceProp {
     _pad: [u8; 4096],
 }
 
-extern "C" {
+unsafe extern "C" {
     // --- Device ---
     pub fn cudaGetDeviceCount(count: *mut i32) -> i32;
     pub fn cudaSetDevice(device: i32) -> i32;

crates/xserv-cuda/src/memory.rs

@@ -48,26 +48,30 @@ impl GpuBuffer {
     /// Safety: `src` must remain valid until the stream operation completes.
     pub unsafe fn copy_from_host_async(&mut self, src: &[u8], stream: &CudaStream) -> Result<()> {
         assert!(src.len() <= self.len);
-        error::check(ffi::cudaMemcpyAsync(
-            self.ptr,
-            src.as_ptr(),
-            src.len(),
-            ffi::CUDA_MEMCPY_H2D,
-            stream.as_raw(),
-        ))
+        unsafe {
+            error::check(ffi::cudaMemcpyAsync(
+                self.ptr,
+                src.as_ptr(),
+                src.len(),
+                ffi::CUDA_MEMCPY_H2D,
+                stream.as_raw(),
+            ))
+        }
     }
 
     /// Async copy from device to host on the given stream.
     /// Safety: `dst` must remain valid until the stream operation completes.
     pub unsafe fn copy_to_host_async(&self, dst: &mut [u8], stream: &CudaStream) -> Result<()> {
         assert!(dst.len() <= self.len);
-        error::check(ffi::cudaMemcpyAsync(
-            dst.as_mut_ptr(),
-            self.ptr,
-            dst.len(),
-            ffi::CUDA_MEMCPY_D2H,
-            stream.as_raw(),
-        ))
+        unsafe {
+            error::check(ffi::cudaMemcpyAsync(
+                dst.as_mut_ptr(),
+                self.ptr,
+                dst.len(),
+                ffi::CUDA_MEMCPY_D2H,
+                stream.as_raw(),
+            ))
+        }
     }
 
     /// Copy from another GPU buffer (D2D).

crates/xserv-cuda/tests/integration.rs

@@ -7,7 +7,8 @@ fn test_device_info() {
 
     let info = device::device_info(0).expect("failed to get device info");
     println!("GPU 0: {}", info.name);
-    println!("  Memory: {} MB", info.total_memory / (1024 * 1024));
+    println!("  Total Memory: {} MB", info.total_memory / (1024 * 1024));
+    println!("  Free Memory:  {} MB", info.free_memory / (1024 * 1024));
     println!(
         "  Compute Capability: {}.{}",
         info.compute_major, info.compute_minor
@@ -17,7 +18,7 @@ fn test_device_info() {
     println!("  Warp Size: {}", info.warp_size);
     println!("  Max Threads/Block: {}", info.max_threads_per_block);
 
-    assert!(info.total_memory > 0);
+    assert!(info.total_memory > 30 * 1024 * 1024 * 1024); // 5090 has 32GB
     assert!(info.sm_count > 0);
 }