lib: Introduce krun_has_feature() API

Introduce a function to query at runtime whether a specific feature
was enabled at build time. This allows applications to check for
optional capabilities before attempting to use them.

This is especially useful for our tests and examples.

Signed-off-by: Matej Hrica <mhrica@redhat.com>

Author: mtjhrc

include/libkrun.h

@@ -977,6 +977,20 @@ int32_t krun_set_nested_virt(uint32_t ctx_id, bool enabled);
  */
 int32_t krun_check_nested_virt(void);
 
+/**
+ * Checks if a specific feature was enabled at build time.
+ *
+ * Arguments:
+ *  "feature" - a null-terminated string representing the feature name.
+ *              Supported feature names: "NET", "BLK", "GPU", "SND", "INPUT",
+ *              "EFI", "TEE", "SEV", "TDX", "NITRO", "VIRGL_RESOURCE_MAP2"
+ *
+ * Returns:
+ *  1 if the feature is supported, 0 if not supported, or a negative error
+ *  number on failure (e.g., -EINVAL for invalid input).
+ */
+int32_t krun_has_feature(const char *feature);
+
 /**
  * Get the maximum number of vCPUs supported by the hypervisor.
  *

src/libkrun/src/lib.rs

@@ -1844,6 +1844,36 @@ pub unsafe extern "C" fn krun_check_nested_virt() -> i32 {
     -libc::EOPNOTSUPP
 }
 
+#[allow(clippy::missing_safety_doc)]
+#[no_mangle]
+pub unsafe extern "C" fn krun_has_feature(feature: *const c_char) -> i32 {
+    if feature.is_null() {
+        return -libc::EINVAL;
+    }
+
+    let feature = match CStr::from_ptr(feature).to_str() {
+        Ok(f) => f,
+        Err(_) => return -libc::EINVAL,
+    };
+
+    let supported = match feature {
+        "NET" => cfg!(feature = "net"),
+        "BLK" => cfg!(feature = "blk"),
+        "GPU" => cfg!(feature = "gpu"),
+        "SND" => cfg!(feature = "snd"),
+        "INPUT" => cfg!(feature = "input"),
+        "EFI" => cfg!(feature = "efi"),
+        "TEE" => cfg!(feature = "tee"),
+        "SEV" => cfg!(feature = "amd-sev"),
+        "TDX" => cfg!(feature = "tdx"),
+        "NITRO" => cfg!(feature = "nitro"),
+        "VIRGL_RESOURCE_MAP2" => cfg!(feature = "virgl_resource_map2"),
+        _ => return -libc::EINVAL,
+    };
+
+    supported as i32
+}
+
 /// Gets the maximum number of vCPUs supported by the hypervisor.
 ///
 /// Returns the maximum number of vCPUs that can be created by this hypervisor,