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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