From 660c4548f2da83b938fba88e39020eae2796dc0e Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Tue, 25 Aug 2026 22:49:44 +0200
Subject: kernel/fs: ext2: add a simple write batching type

---
 kernel/CMakeLists.txt                         |  1 +
 kernel/kernel/filesystem/ext2/filesystem.hpp  |  2 +
 kernel/kernel/filesystem/ext2/write_batch.cpp | 67 +++++++++++++++++++++++++++
 kernel/kernel/filesystem/ext2/write_batch.hpp | 53 +++++++++++++++++++++
 4 files changed, 123 insertions(+)
 create mode 100644 kernel/kernel/filesystem/ext2/write_batch.cpp
 create mode 100644 kernel/kernel/filesystem/ext2/write_batch.hpp

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index 1a5e2421..35c3a957 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -80,6 +80,7 @@ target_sources("kernel_lib" PRIVATE
     "kernel/filesystem/ext2/filesystem.cpp"
     "kernel/filesystem/ext2/inode.cpp"
     "kernel/filesystem/ext2/module.cpp"
+    "kernel/filesystem/ext2/write_batch.cpp"
 
     # Rootfs Filesystem
     "kernel/filesystem/rootfs/filesystem.cpp"
diff --git a/kernel/kernel/filesystem/ext2/filesystem.hpp b/kernel/kernel/filesystem/ext2/filesystem.hpp
index 93836b91..f43e357c 100644
--- a/kernel/kernel/filesystem/ext2/filesystem.hpp
+++ b/kernel/kernel/filesystem/ext2/filesystem.hpp
@@ -191,6 +191,8 @@ namespace kernel::filesystem::ext2
         -> kstd::result<void>;
 
   private:
+    friend struct write_batch;
+
     //! Allocate a single inode in the file system.
     //!
     //! @param state The driver state to operate on.
diff --git a/kernel/kernel/filesystem/ext2/write_batch.cpp b/kernel/kernel/filesystem/ext2/write_batch.cpp
new file mode 100644
index 00000000..e8663d21
--- /dev/null
+++ b/kernel/kernel/filesystem/ext2/write_batch.cpp
@@ -0,0 +1,67 @@
+#include <kernel/filesystem/ext2/write_batch.hpp>
+
+#include <kernel/filesystem/ext2/filesystem.hpp>
+#include <kernel/filesystem/ext2/inode.hpp>
+#include <kernel/filesystem/ext2/mount_state.hpp>
+
+#include <kapi/system.hpp>
+
+#include <algorithm>
+#include <cstddef>
+#include <ranges>
+
+namespace kernel::filesystem::ext2
+{
+
+  write_batch::write_batch(filesystem & filesystem, mount_state & state)
+      : m_filesystem{filesystem}
+      , m_state{state}
+  {}
+
+  write_batch::~write_batch()
+  {
+    std::ranges::for_each(m_dirty_groups, [this](auto index) {
+      auto & descriptor = m_state.block_group_descriptors.at(index);
+      auto result = m_filesystem.write_block_group_descriptor(descriptor, index, m_state);
+
+      if (!result)
+      {
+        kapi::system::panic("[FS:ext2] failed to write block groups descriptor", result.error());
+      }
+    });
+
+    if (!m_dirty_groups.empty())
+    {
+      auto result = m_filesystem.write_superblock(m_state);
+      if (!result)
+      {
+        kapi::system::panic("[FS:ext2] failed to write superblock", result.error());
+      }
+    }
+
+    std::ranges::for_each(m_dirty_inodes, [this](auto inode) {
+      auto result = m_filesystem.write_inode(inode->number(), inode->data(), m_state);
+      if (!result)
+      {
+        kapi::system::panic("[FS:ext2] failed to write inode", result.error());
+      }
+    });
+  }
+
+  auto write_batch::mark_group(std::size_t index) -> void
+  {
+    if (std::ranges::find(m_dirty_groups, index) == std::ranges::end(m_dirty_groups))
+    {
+      m_dirty_groups.push_back(index);
+    }
+  }
+
+  auto write_batch::mark_inode(inode & inode) -> void
+  {
+    if (std::ranges::find(m_dirty_inodes, &inode) == std::ranges::end(m_dirty_inodes))
+    {
+      m_dirty_inodes.push_back(&inode);
+    }
+  }
+
+}  // namespace kernel::filesystem::ext2
diff --git a/kernel/kernel/filesystem/ext2/write_batch.hpp b/kernel/kernel/filesystem/ext2/write_batch.hpp
new file mode 100644
index 00000000..103684ac
--- /dev/null
+++ b/kernel/kernel/filesystem/ext2/write_batch.hpp
@@ -0,0 +1,53 @@
+#ifndef TEACHOS_KERNEL_FILESYSTEM_EXT2_WRITE_BATCH
+#define TEACHOS_KERNEL_FILESYSTEM_EXT2_WRITE_BATCH
+
+#include <kstd/vector.hpp>
+
+#include <cstddef>
+
+namespace kernel::filesystem::ext2
+{
+
+  struct filesystem;
+  struct inode;
+  struct mount_state;
+
+  //! A RAII write batching type.
+  //!
+  //! Any metadata writes are first appended to the batch. On destruction, the write is committed to the filesystem.
+  struct write_batch
+  {
+    //! Construct a new write batch for the given filesystem and mount state.
+    //!
+    //! @param filesystem The filesystem driver to use for writes.
+    //! @param state The driver state to operate on.
+    write_batch(filesystem & filesystem, mount_state & state);
+
+    write_batch(write_batch const &) = delete;
+    write_batch(write_batch &&) = delete;
+    auto operator=(write_batch const &) = delete;
+    auto operator=(write_batch &&) = delete;
+
+    //! Commit and destroy the batch.
+    ~write_batch();
+
+    //! Mark the group with the given index as dirty.
+    //!
+    //! @param index The index of the group to mark.
+    auto mark_group(std::size_t index) -> void;
+
+    //! Mark the given inode as dirty.
+    //!
+    //! @param inode The inode to mark.
+    auto mark_inode(inode & inode) -> void;
+
+  private:
+    filesystem & m_filesystem;
+    mount_state & m_state;
+    kstd::vector<std::size_t> m_dirty_groups{};
+    kstd::vector<inode *> m_dirty_inodes{};
+  };
+
+}  // namespace kernel::filesystem::ext2
+
+#endif
-- 
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