create a kernel buffer from user-level

["Feng Xian" <feng.xian@xxxxxxxxx>]

I am doing a project related to thread scheduling. This project needs communication between kernel and user-level applications. Basically, the user-level application sets or unset a bit in a bit vector, according to the application's status (this part is not related to this question, so I skip it). Then the kernel reads the bit vector everytime it schedules a thread.

My question is where to allocate the bit vector.

1. If I allocate the bit vector in user-level, then everytime the kernel wants to read the bit vector, I has to do a copy_from_user(). I tried this solution, this incurs a lot of overhead and also crash the os. Since the copy_from_user() needs to look up the virtual address which corresponds to the starting address of bit-vector, it will cause paging in the middle of scheduling. Is there any other way that the kernel can directly access user-level space without doing copying and address translation?

2. If I allocate the bit vector directly in the kernel space. How can I do this? Is it possible to create an extra system call that allows user-level program to allocate a kernel buffer?

Could anyone help me out on this? Thanks!

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