Messages in this thread | | | Date | Wed, 22 Mar 2000 16:24:24 +0200 (EET) | From | Venetis Ioannis <> | Subject | Mapping kernel memory to user space from within a system call |
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Hi,
I am currently implementing a user-level threads library. I am adding also a new system call to the kernel, which will be used by this threads library. The system call must do the following :
a) Allocate a memory page in the kernel (I do it with __get_free_page(GFP_KERNEL)). b) Map this page to the processes address space. c) Create some more kernel threads (I do this with do_fork() and the CLONE_VM flag set and on top of these kernel threads I will execute the user-level threads that my library implements).
The idea is to have a very fast communication path between the kernel and my library. This path can be used to communicate requirements by the library to the kernel (how many kernel threads do I need at any given moment?) and scheduling decissions (preemptions of kernel threads) by the kernel to the library. By setting the CLONE_VM flag in do_fork() I want all the kernel threads of the application to be able to have access to this page. I have made some tests and everything works fine except of the mapping of that page to the processes address space. I have tried to use do_mmap() after opening /dev/kmem. I also used mem_map_reserve(MAP_NR(Pointer returned from __get_free_page())). This works some times, some times I get oopses and also I think this is not very elegant. Is there a better way to do the mapping (through the page tables perhaps)? I also want that this page will never be swapped out, for performance reasons.
Any help, links, comments and suggestions are appreciated.
Ioannis Venetis
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