From 58c6d30f6a29420356b349888b2509b44cadc8c9 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 18 Jul 2021 01:29:54 +0200
Subject: [PATCH] Kernel/Ext2FS: Cache the root inode in a member variable

We often get queried for the root inode, and it will always be cached
in memory anyway, so let's make Ext2FS::root_inode() fast by keeping
the root inode in a dedicated member variable.
---
 Kernel/FileSystem/Ext2FileSystem.cpp | 11 +++++++++--
 Kernel/FileSystem/Ext2FileSystem.h   |  3 ++-
 Kernel/FileSystem/FileSystem.h       |  2 +-
 Kernel/FileSystem/Mount.h            |  1 +
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/Kernel/FileSystem/Ext2FileSystem.cpp b/Kernel/FileSystem/Ext2FileSystem.cpp
index 1966a0de14..b5e4d58813 100644
--- a/Kernel/FileSystem/Ext2FileSystem.cpp
+++ b/Kernel/FileSystem/Ext2FileSystem.cpp
@@ -145,12 +145,18 @@ bool Ext2FS::initialize()
         }
     }
 
+    m_root_inode = static_ptr_cast<Ext2FSInode>(get_inode({ fsid(), EXT2_ROOT_INO }));
+    if (!m_root_inode) {
+        dbgln("Ext2FS: failed to acquire root inode");
+        return false;
+    }
+
     return true;
 }
 
 NonnullRefPtr<Inode> Ext2FS::root_inode() const
 {
-    return *get_inode({ fsid(), EXT2_ROOT_INO });
+    return *m_root_inode;
 }
 
 bool Ext2FS::find_block_containing_inode(InodeIndex inode, BlockIndex& block_index, unsigned& offset) const
@@ -1778,7 +1784,7 @@ unsigned Ext2FS::free_inode_count() const
     return super_block().s_free_inodes_count;
 }
 
-KResult Ext2FS::prepare_to_unmount() const
+KResult Ext2FS::prepare_to_unmount()
 {
     MutexLocker locker(m_lock);
 
@@ -1788,6 +1794,7 @@ KResult Ext2FS::prepare_to_unmount() const
     }
 
     m_inode_cache.clear();
+    m_root_inode = nullptr;
     return KSuccess;
 }
 }
diff --git a/Kernel/FileSystem/Ext2FileSystem.h b/Kernel/FileSystem/Ext2FileSystem.h
index 65cc380efb..c71eefca76 100644
--- a/Kernel/FileSystem/Ext2FileSystem.h
+++ b/Kernel/FileSystem/Ext2FileSystem.h
@@ -99,7 +99,7 @@ public:
     virtual unsigned total_inode_count() const override;
     virtual unsigned free_inode_count() const override;
 
-    virtual KResult prepare_to_unmount() const override;
+    virtual KResult prepare_to_unmount() override;
 
     virtual bool supports_watchers() const override { return true; }
 
@@ -183,6 +183,7 @@ private:
     KResult update_bitmap_block(BlockIndex bitmap_block, size_t bit_index, bool new_state, u32& super_block_counter, u16& group_descriptor_counter);
 
     Vector<OwnPtr<CachedBitmap>> m_cached_bitmaps;
+    RefPtr<Ext2FSInode> m_root_inode;
 };
 
 inline Ext2FS& Ext2FSInode::fs()
diff --git a/Kernel/FileSystem/FileSystem.h b/Kernel/FileSystem/FileSystem.h
index 0693b46b80..512a0c165f 100644
--- a/Kernel/FileSystem/FileSystem.h
+++ b/Kernel/FileSystem/FileSystem.h
@@ -43,7 +43,7 @@ public:
     virtual unsigned total_inode_count() const { return 0; }
     virtual unsigned free_inode_count() const { return 0; }
 
-    virtual KResult prepare_to_unmount() const { return KSuccess; }
+    virtual KResult prepare_to_unmount() { return KSuccess; }
 
     struct DirectoryEntryView {
         DirectoryEntryView(const StringView& name, InodeIdentifier, u8 file_type);
diff --git a/Kernel/FileSystem/Mount.h b/Kernel/FileSystem/Mount.h
index e4a8782971..57790ad043 100644
--- a/Kernel/FileSystem/Mount.h
+++ b/Kernel/FileSystem/Mount.h
@@ -23,6 +23,7 @@ public:
     Inode& guest() { return *m_guest; }
 
     FileSystem const& guest_fs() const { return *m_guest_fs; }
+    FileSystem& guest_fs() { return *m_guest_fs; }
 
     String absolute_path() const;