Automatically call Inode::flush_metadata() before an Inode is destroyed.

Use a little template magic to have Retainable::release() call out to
T::will_be_destroyed() if such a function exists before actually calling
the destructor. This gives us full access to virtual functions in the
pre-destruction code.

AK/Retainable.h

@@ -1,39 +1,54 @@
 #pragma once
 
 #include "Assertions.h"
+#include "StdLibExtras.h"
 
 namespace AK {
 
+template<class T>
+constexpr auto call_will_be_destroyed_if_present(T* object) -> decltype(object->will_be_destroyed(), TrueType { })
+{
+    object->will_be_destroyed();
+    return { };
+}
+
+constexpr auto call_will_be_destroyed_if_present(...) -> FalseType
+{
+    return { };
+}
+
 template<typename T>
 class Retainable {
 public:
     void retain()
     {
-        ASSERT(m_retainCount);
+        ASSERT(m_retain_count);
-        ++m_retainCount;
+        ++m_retain_count;
     }
 
     void release()
     {
-        ASSERT(m_retainCount);
+        ASSERT(m_retain_count);
-        if (!--m_retainCount)
+        if (!--m_retain_count) {
+            call_will_be_destroyed_if_present(static_cast<T*>(this));
             delete static_cast<T*>(this);
+        }
     }
 
-    int retainCount() const
+    int retain_count() const
     {
-        return m_retainCount;
+        return m_retain_count;
     }
 
 protected:
     Retainable() { }
     ~Retainable()
     {
-        ASSERT(!m_retainCount);
+        ASSERT(!m_retain_count);
     }
 
 private:
-    int m_retainCount { 1 };
+    int m_retain_count { 1 };
 };
 
 }

Kernel/ProcFileSystem.cpp

@@ -83,7 +83,7 @@ ByteBuffer procfs$pid_vmo(Process& process)
             region->vmo().is_anonymous() ? "anonymous" : "file-backed",
             region->vmo().name().characters(),
             &region->vmo(),
-            region->vmo().retainCount());
+            region->vmo().retain_count());
         for (size_t i = 0; i < region->vmo().page_count(); ++i) {
             auto& physical_page = region->vmo().physical_pages()[i];
             ptr += ksprintf(ptr, "P%x%s(%u) ",
@@ -205,7 +205,7 @@ ByteBuffer procfs$mm()
         ptr += ksprintf(ptr, "VMO: %p %s(%u): p:%4u %s\n",
             vmo,
             vmo->is_anonymous() ? "anon" : "file",
-            vmo->retainCount(),
+            vmo->retain_count(),
             vmo->page_count(),
             vmo->name().characters());
     }

Kernel/Process.cpp

@@ -1104,7 +1104,7 @@ int Process::sys$utime(const char* pathname, const Unix::utimbuf* buf)
         atime = now;
     }
     inode.set_atime(atime);
-    inode.set_mtime(atime);
+    inode.set_mtime(mtime);
     inode.flush_metadata();
     return 0;
 }

VirtualFileSystem/Ext2FileSystem.cpp

@@ -317,6 +317,7 @@ void Ext2FSInode::flush_metadata()
     m_raw_inode.i_dtime = m_metadata.dtime;
     m_raw_inode.i_blocks = m_metadata.blockCount;
     fs().write_ext2_inode(index(), m_raw_inode);
+    set_metadata_dirty(false);
 }
 
 RetainPtr<Inode> Ext2FS::get_inode(InodeIdentifier inode) const

VirtualFileSystem/FileSystem.cpp

@@ -129,6 +129,12 @@ Inode::~Inode()
 {
 }
 
+void Inode::will_be_destroyed()
+{
+    if (m_metadata_dirty)
+        flush_metadata();
+}
+
 int Inode::set_atime(Unix::time_t ts)
 {
     if (fs().is_readonly())
@@ -136,7 +142,7 @@ int Inode::set_atime(Unix::time_t ts)
     if (m_metadata.atime == ts)
         return 0;
     m_metadata.atime = ts;
-    m_dirty = true;
+    m_metadata_dirty = true;
     return 0;
 }
 
@@ -147,7 +153,7 @@ int Inode::set_ctime(Unix::time_t ts)
     if (m_metadata.ctime == ts)
         return 0;
     m_metadata.ctime = ts;
-    m_dirty = true;
+    m_metadata_dirty = true;
     return 0;
 }
 
@@ -158,6 +164,6 @@ int Inode::set_mtime(Unix::time_t ts)
     if (m_metadata.mtime == ts)
         return 0;
     m_metadata.mtime = ts;
-    m_dirty = true;
+    m_metadata_dirty = true;
     return 0;
 }

VirtualFileSystem/FileSystem.h

@@ -87,7 +87,7 @@ public:
     virtual InodeIdentifier lookup(const String& name) = 0;
     virtual String reverse_lookup(InodeIdentifier) = 0;
 
-    bool is_dirty() const { return m_dirty; }
+    bool is_metadata_dirty() const { return m_metadata_dirty; }
 
     int set_atime(Unix::time_t);
     int set_ctime(Unix::time_t);
@@ -95,6 +95,8 @@ public:
 
     virtual void flush_metadata() = 0;
 
+    void will_be_destroyed();
+
 protected:
     Inode(FS& fs, unsigned index)
         : m_fs(fs)
@@ -103,13 +105,13 @@ protected:
     }
 
     virtual void populate_metadata() const = 0;
-    void set_dirty(bool b) { m_dirty = b; }
+    void set_metadata_dirty(bool b) { m_metadata_dirty = b; }
 
     mutable InodeMetadata m_metadata;
 private:
     FS& m_fs;
     unsigned m_index { 0 };
-    bool m_dirty { false };
+    bool m_metadata_dirty { false };
 };
 
 inline FS* InodeIdentifier::fs()