Kernel/FileSystem: Make Inode::{write,read}_bytes methods non-virtual

We make these methods non-virtual because we want to ensure we properly
enforce locking of the m_inode_lock mutex. Also, for write operations,
we want to call prepare_to_write_data before the actual write. The
previous design required us to ensure the callers do that at various
places which lead to hard-to-find bugs. By moving everything to a place
where we call prepare_to_write_data only once, we eliminate a possibilty
of forgeting to call it on some code path in the kernel.

Kernel/FileSystem/Plan9FileSystem.cpp

@@ -718,7 +718,7 @@ ErrorOr<void> Plan9FSInode::ensure_open_for_mode(int mode)
     return fs().post_message_and_wait_for_a_reply(message);
 }
 
-ErrorOr<size_t> Plan9FSInode::read_bytes(off_t offset, size_t size, UserOrKernelBuffer& buffer, OpenFileDescription*) const
+ErrorOr<size_t> Plan9FSInode::read_bytes_locked(off_t offset, size_t size, UserOrKernelBuffer& buffer, OpenFileDescription*) const
 {
     TRY(const_cast<Plan9FSInode&>(*this).ensure_open_for_mode(O_RDONLY));
 
@@ -750,7 +750,7 @@ ErrorOr<size_t> Plan9FSInode::read_bytes(off_t offset, size_t size, UserOrKernel
     return nread;
 }
 
-ErrorOr<size_t> Plan9FSInode::write_bytes(off_t offset, size_t size, UserOrKernelBuffer const& data, OpenFileDescription*)
+ErrorOr<size_t> Plan9FSInode::write_bytes_locked(off_t offset, size_t size, UserOrKernelBuffer const& data, OpenFileDescription*)
 {
     TRY(ensure_open_for_mode(O_WRONLY));
     size = fs().adjust_buffer_size(size);