[mt2002]

Hey everyone

I have a design related question using C++. Im rewriting my paging code (again! I just cant seem to find a nice interface for it!), however there is one thing that has been a little bothering me.

I have two structures defined as follows. Please keep in mind these are hardware structures, so I cannot change the format of any of the structs.

//! page table entry
struct page_pte {

	//! page flags
	uint8_t		m_flags;

	//! physical frame address of page (Must be 4K aligned)
	uint8_t		m_addrLo;
	uint16_t	m_addrHi;
};

//! page directory entry
struct page_pde {

	//! page directory flags
	uint8_t		m_flags;

	//! base address of page table (Must be 4K aligned)
	uint8_t		m_addrLo;
	uint16_t	m_addrHi;
};

The only difference between these two structures are 3 bits. These 3 bits are reserved in page_pte but are used in page_pde. These bits are inside of the structs flags member.

Because of this, they have practically the same structure, format, everything--and are very interchangeable. The only thing that differs them is those 3 single bits within their flags member.

My question is: Should I combine them into a single data structure, or keep them separate? If I keep them separate, I will be having alot of duplicate routines working on both data structures as they are practically the same. If I combine them, I lose the aspect of object orientation.

What do you think I should do? I have been thinking about this for some time now, and cannot seem to be able to decide on what I should do here.

Thanks for any suggestions!

[lotuseclat79]

Hi mt2002,

The so-called duplicate routines are not really working on the same data structure, but different instances of nearly identical data structures - not the same.

I would keep them separate, as the 3 reserved bits in the pte are serving a very specific purpose not shared by the pde.

If you were to combine them, the only differentiation would have to be that of the types of each structure, and you would still have to make that determination in the code. It is a trade-off, and the better trade-off is not to introduce confusion when separation of purpose fits the need.

-- Tom

[mt2002]

Thanks

I am going to keep them separate then for now and see how it goes I decided to just create two header files to separate them: pde.h and pdt.h.

Instead of creating routines to interface with them (As I was originally going to do) I decided to just keep the members public as only the physical frame manager will be working with it anyways.

If there are any further suggestions, please feel free to let me know!