Kernel+LibC: Implement fsync

Author: https://github.com/SeekingBlues
Commit: a81b21c1a7
Pull-request: https://github.com/SerenityOS/serenity/pull/9983

Kernel/FileSystem/Inode.cpp

@@ -29,7 +29,7 @@ SpinlockProtected<Inode::AllInstancesList>& Inode::all_instances()
     return s_all_instances;
 }
 
-void Inode::sync()
+void Inode::sync_all()
 {
     NonnullRefPtrVector<Inode, 32> inodes;
     Inode::all_instances().with([&](auto& all_inodes) {
@@ -45,6 +45,13 @@ void Inode::sync()
     }
 }
 
+void Inode::sync()
+{
+    if (is_metadata_dirty())
+        flush_metadata();
+    fs().flush_writes();
+}
+
 KResultOr<NonnullOwnPtr<KBuffer>> Inode::read_entire(OpenFileDescription* description) const
 {
     auto builder = TRY(KBufferBuilder::try_create());