From ef124ea26ebe98f16e0e8fb204ec1f419bf656ee Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Fri, 24 Jul 2026 09:11:12 +0200
Subject: kapi: add find overload to find composed interfaces

---
 kapi/kapi/devices/interface_registry.hpp   |  7 +++++++
 kernel/kapi/devices/interface_registry.cpp | 14 ++++++++++++++
 kernel/kernel/filesystem/device_inode.cpp  | 24 ++++++++++++++++++++++--
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/kapi/kapi/devices/interface_registry.hpp b/kapi/kapi/devices/interface_registry.hpp
index ae8b5c1a..b1dfa08e 100644
--- a/kapi/kapi/devices/interface_registry.hpp
+++ b/kapi/kapi/devices/interface_registry.hpp
@@ -121,6 +121,13 @@ namespace kapi::devices
     //! @return An entry representing the published interface if it exists, an error otherwise.
     [[nodiscard]] auto find(interface interface, std::string_view name) const -> kstd::result<entry>;
 
+    //! Find an entry for a given interface on a specific device.
+    //!
+    //! @param interface The interface to look for.
+    //! @param device The device to look for.
+    //! @return An entry representing the published interface if it exists, an error otherwise.
+    [[nodiscard]] auto find(interface interface, device const & device) const -> kstd::result<entry>;
+
     //! Find an entry for a given interface on a device with the given name.
     //!
     //! @tparam Interface The interface type to look for.
diff --git a/kernel/kapi/devices/interface_registry.cpp b/kernel/kapi/devices/interface_registry.cpp
index da3d080a..d959c857 100644
--- a/kernel/kapi/devices/interface_registry.cpp
+++ b/kernel/kapi/devices/interface_registry.cpp
@@ -97,6 +97,20 @@ namespace kapi::devices
     return *found;
   }
 
+  auto interface_registry::find(interface interface, device const & device) const -> kstd::result<entry>
+  {
+    auto found = std::ranges::find_if(m_entries, [&](auto e) {
+      auto locked_device = e.device();
+      return e.interface() == interface && locked_device && locked_device.get() == &device;
+    });
+    if (found == m_entries.cend())
+    {
+      return kstd::failure(make_error_code(kstd::errc::no_such_device));
+    }
+
+    return *found;
+  }
+
 }  // namespace kapi::devices
 
 namespace kapi::test_support::devices
diff --git a/kernel/kernel/filesystem/device_inode.cpp b/kernel/kernel/filesystem/device_inode.cpp
index 33037a52..0ff8dce6 100644
--- a/kernel/kernel/filesystem/device_inode.cpp
+++ b/kernel/kernel/filesystem/device_inode.cpp
@@ -16,6 +16,26 @@
 
 #include <optional>
 
+namespace
+{
+  template<typename Interface>
+  auto resolve(kapi::devices::device & device) -> Interface *
+  {
+    if (auto * direct = device.as<Interface>())
+    {
+      return direct;
+    }
+
+    auto found = kapi::devices::interface_registry::get().find(Interface::id, device);
+    if (!found)
+    {
+      return nullptr;
+    }
+
+    return found->template as<Interface>();
+  }
+}  // namespace
+
 namespace kernel::filesystem
 {
   device_inode::device_inode(kstd::shared_ptr<kapi::devices::device> const & device)
@@ -41,7 +61,7 @@ namespace kernel::filesystem
   auto device_inode::read(void * buffer, kstd::units::bytes offset, kstd::units::bytes size) const
       -> kstd::result<kstd::units::bytes>
   {
-    if (auto block_device = m_device->as<kapi::devices::block_device>())
+    if (auto block_device = resolve<kapi::devices::block_device>(*m_device))
     {
       return devices::block_device_utils::read(*block_device, buffer, offset, size);
     }
@@ -52,7 +72,7 @@ namespace kernel::filesystem
   auto device_inode::write(void const * buffer, kstd::units::bytes offset, kstd::units::bytes size)
       -> kstd::result<kstd::units::bytes>
   {
-    if (auto block_device = m_device->as<kapi::devices::block_device>())
+    if (auto block_device = resolve<kapi::devices::block_device>(*m_device))
     {
       return devices::block_device_utils::write(*block_device, buffer, offset, size);
     }
-- 
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