How to write kernel space memory (physical address) to a file using O_DIRECT?

Your problem looks a little strange. Since you are programming quite near to the hardware, you might consider using direct memory access (DMA). This might be a bit tricky, since you need to understand paging and parts of the I/O mechanism.

You might want to read that.

I tested tonight , if use O_DIRECT your write will be conditional.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.