From 2f4001cdb1f528d8a0d255d81ac3a8b9aa522fac Mon Sep 17 00:00:00 2001
From: Lukas Oesch <lukasoesch20@gmail.com>
Date: Sat, 7 Mar 2026 13:55:40 +0100
Subject: implement first draft of a file_descriptor_table and
 open_file_description

---
 kernel/filesystem/src/file.cpp                  |  6 ++
 kernel/filesystem/src/file_descriptor_table.cpp | 81 +++++++++++++++++++++++++
 kernel/filesystem/src/open_file_description.cpp | 24 ++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 kernel/filesystem/src/file.cpp
 create mode 100644 kernel/filesystem/src/file_descriptor_table.cpp
 create mode 100644 kernel/filesystem/src/open_file_description.cpp

(limited to 'kernel/filesystem/src')

diff --git a/kernel/filesystem/src/file.cpp b/kernel/filesystem/src/file.cpp
new file mode 100644
index 0000000..c67ad1a
--- /dev/null
+++ b/kernel/filesystem/src/file.cpp
@@ -0,0 +1,6 @@
+#include "filesystem/file.hpp"
+
+namespace filesystem
+{
+  // TODO BA-FS26
+}
\ No newline at end of file
diff --git a/kernel/filesystem/src/file_descriptor_table.cpp b/kernel/filesystem/src/file_descriptor_table.cpp
new file mode 100644
index 0000000..0c79431
--- /dev/null
+++ b/kernel/filesystem/src/file_descriptor_table.cpp
@@ -0,0 +1,81 @@
+#include "filesystem/file_descriptor_table.hpp"
+
+#include "kapi/system.hpp"
+
+#include "filesystem/open_file_description.hpp"
+
+#include <algorithm>
+#include <cstddef>
+#include <optional>
+
+namespace filesystem
+{
+  namespace
+  {
+    constinit auto static global_file_descriptor_table = std::optional<file_descriptor_table>{};
+  }  // namespace
+
+  auto file_descriptor_table::init() -> void
+  {
+    if (global_file_descriptor_table)
+    {
+      kapi::system::panic("[FILESYSTEM] File descriptor table has already been initialized.");
+    }
+
+    global_file_descriptor_table.emplace(file_descriptor_table{});
+  }
+
+  auto file_descriptor_table::get() -> file_descriptor_table &
+  {
+    if (!global_file_descriptor_table)
+    {
+      kapi::system::panic("[FILESYSTEM] File descriptor table has not been initialized.");
+    }
+
+    return *global_file_descriptor_table;
+  }
+
+  auto file_descriptor_table::add_file(open_file_description & f) -> int
+  {
+    auto it = std::ranges::find(m_open_files, nullptr);
+    if (it != m_open_files.end())
+    {
+      *it = &f;
+      return static_cast<int>(it - m_open_files.begin());
+    }
+
+    return -1;
+  }
+
+  auto file_descriptor_table::get_file(int fd) -> open_file_description &
+  {
+    if (fd < 0)
+    {
+      kapi::system::panic("[FILESYSTEM] get_file called with negative descriptor.");
+    }
+
+    auto const index = static_cast<size_t>(fd);
+    if (index >= m_open_files.size() || m_open_files[index] == nullptr)
+    {
+      kapi::system::panic("[FILESYSTEM] get_file called with invalid descriptor.");
+    }
+
+    return *m_open_files[index];
+  }
+
+  auto file_descriptor_table::remove_file(int fd) -> void
+  {
+    if (fd < 0)
+    {
+      kapi::system::panic("[FILESYSTEM] remove_file called with negative descriptor.");
+    }
+
+    auto const index = static_cast<size_t>(fd);
+    if (index >= m_open_files.size())
+    {
+      kapi::system::panic("[FILESYSTEM] remove_file called with out-of-range descriptor.");
+    }
+
+    m_open_files[index] = nullptr;
+  }
+}  // namespace filesystem
\ No newline at end of file
diff --git a/kernel/filesystem/src/open_file_description.cpp b/kernel/filesystem/src/open_file_description.cpp
new file mode 100644
index 0000000..8c20397
--- /dev/null
+++ b/kernel/filesystem/src/open_file_description.cpp
@@ -0,0 +1,24 @@
+#include "filesystem/open_file_description.hpp"
+
+#include "filesystem/file.hpp"
+
+#include <cstddef>
+
+namespace filesystem
+{
+  auto open_file_description::read(void * buffer, size_t size) -> size_t
+  {
+    // TODO BA-FS26 nullptr check
+    auto read_bytes = m_file->read(buffer, m_offset, size);
+    m_offset += read_bytes;
+    return read_bytes;
+  }
+
+  auto open_file_description::write(void const * buffer, size_t size) -> size_t
+  {
+    // TODO BA-FS26 nullptr check
+    auto written_bytes = m_file->write(buffer, m_offset, size);
+    m_offset += written_bytes;
+    return written_bytes;
+  }
+}  // namespace filesystem
\ No newline at end of file
-- 
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