From 2b542cb4d5f2302f41d478892694124472cde8b0 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Thu, 30 Jul 2026 13:45:18 +0200
Subject: kernel: add support for character devices

---
 kernel/kernel/drivers/storage/ram_disk.hpp      |  1 +
 kernel/kernel/filesystem/device_inode.cpp       | 19 ++++++++++++++++++-
 kernel/kernel/filesystem/device_inode.hpp       | 10 ++++++++--
 kernel/kernel/filesystem/file_type_bindings.hpp |  3 ++-
 4 files changed, 29 insertions(+), 4 deletions(-)

(limited to 'kernel')

diff --git a/kernel/kernel/drivers/storage/ram_disk.hpp b/kernel/kernel/drivers/storage/ram_disk.hpp
index d5d54551..45c5bbc2 100644
--- a/kernel/kernel/drivers/storage/ram_disk.hpp
+++ b/kernel/kernel/drivers/storage/ram_disk.hpp
@@ -2,6 +2,7 @@
 #define TEACH_OS_KERNEL_DRIVERS_STORAGE_RAM_DISK_HPP
 
 #include <kapi/boot_modules.hpp>
+#include <kapi/capabilities/facet_id.hpp>
 #include <kapi/devices.hpp>
 
 #include <kstd/result.hpp>
diff --git a/kernel/kernel/filesystem/device_inode.cpp b/kernel/kernel/filesystem/device_inode.cpp
index 4696504e..d6f7637a 100644
--- a/kernel/kernel/filesystem/device_inode.cpp
+++ b/kernel/kernel/filesystem/device_inode.cpp
@@ -14,7 +14,9 @@
 #include <kstd/result.hpp>
 #include <kstd/units.hpp>
 
+#include <cstddef>
 #include <optional>
+#include <span>
 
 namespace kernel::filesystem
 {
@@ -51,6 +53,11 @@ namespace kernel::filesystem
     {
       return devices::block_device_utils::read(*block_device, buffer, offset, size);
     }
+    else if (auto character_device =
+                 kapi::devices::facet_registry::get().resolve<kapi::filesystem::character_special_file>(*m_device))
+    {
+      return character_device->read(std::span{static_cast<std::byte *>(buffer), size.value});
+    }
 
     return kstd::failure(vfs_errc::no_such_device);
   }
@@ -68,6 +75,11 @@ namespace kernel::filesystem
     {
       return devices::block_device_utils::write(*block_device, buffer, offset, size);
     }
+    else if (auto character_device =
+                 kapi::devices::facet_registry::get().resolve<kapi::filesystem::character_special_file>(*m_device))
+    {
+      return character_device->write(std::span{static_cast<std::byte const *>(buffer), size.value});
+    }
 
     return kstd::failure(vfs_errc::no_such_device);
   }
@@ -79,7 +91,12 @@ namespace kernel::filesystem
 
   auto device_inode::is_block_device() const -> bool
   {
-    return true;
+    return kapi::devices::facet_registry::get().resolve<kapi::filesystem::block_special_file>(*m_device);
+  }
+
+  auto device_inode::is_character_device() const -> bool
+  {
+    return kapi::devices::facet_registry::get().resolve<kapi::filesystem::character_special_file>(*m_device);
   }
 
   auto device_inode::status() const -> kstd::result<kapi::filesystem::file_status>
diff --git a/kernel/kernel/filesystem/device_inode.hpp b/kernel/kernel/filesystem/device_inode.hpp
index e2167131..17ebe236 100644
--- a/kernel/kernel/filesystem/device_inode.hpp
+++ b/kernel/kernel/filesystem/device_inode.hpp
@@ -61,11 +61,17 @@ namespace kernel::filesystem
     [[nodiscard]] auto device() const -> kstd::shared_ptr<kapi::devices::device> const &;
 
     /**
-    @brief Check if this inode represents a device.
-    @return returns true, since this inode is a device inode and represents a device.
+    @brief Check if this inode represents a block device.
+    @return true iff. the underlying device is a block device, false otherwise.
     */
     [[nodiscard]] auto is_block_device() const -> bool override;
 
+    /**
+    @brief Check if this inode represents a character device.
+    @return true iff. the underlying device is a character device, false otherwise.
+    */
+    [[nodiscard]] auto is_character_device() const -> bool override;
+
     [[nodiscard]] auto status() const -> kstd::result<kapi::filesystem::file_status> override;
 
     [[nodiscard]] auto raw_device() const -> std::optional<kapi::filesystem::device_number> override;
diff --git a/kernel/kernel/filesystem/file_type_bindings.hpp b/kernel/kernel/filesystem/file_type_bindings.hpp
index ea52972b..b4338024 100644
--- a/kernel/kernel/filesystem/file_type_bindings.hpp
+++ b/kernel/kernel/filesystem/file_type_bindings.hpp
@@ -22,7 +22,8 @@ namespace kernel::filesystem
   //!
   //! This array associates published facets with files types.
   constexpr auto inline file_type_bindings = std::array{
-    file_type_binding{kapi::filesystem::block_special_file::id, file_type::block},
+    file_type_binding{kapi::filesystem::character_special_file::id, file_type::character},
+    file_type_binding{    kapi::filesystem::block_special_file::id,     file_type::block},
   };
 
 }  // namespace kernel::filesystem
-- 
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