[rtl] Shared Memory

["Ian Ridley" <iridley@ingenico.com.au>]

Something that might interest those who use shared memory between RT 
tasks and regular processes. Attached is a patch that I have created 
that allows the sharing of memory between kernel and user space with 
a little more control than just removing the current block on the 
kernel memory. It allows a kernel module to allocate memory that will 
be sharable with user processes. The user processes have a new system 
call "shm_open" which partially mimics the POSIX shared memory (for 
user processes) ie it returns a fd which can be used with mmap to map 
into the users address space.

I've had limited success with this so far, but it will only work for 
2.0.xx kernels. When I get time I might have a look at the mm for 
newer kernels. The patch attached to this mail was made against 
2.0.27 kernel after the RT patch was made. So if your interested try 
it out, but be careful it probably still needs considerable work yet.

Another thing I have been toying with was using shared memory to 
control the RT tasks from the user process. Instead of using a fifo 
to pass control messages to a handler in the module. If the RT task 
structures are placed in shared memory then tasks states can be 
modified. Of course this means that a system call has to be made for 
a reschedule so that the RT scheduler can be told when any RT tasks 
need to be rechecked. Prehaps this could be investigated further, but 
I think that added a reschedule system call should cause to many 
problems and can still be flexible enought to cope with different 
scheduler modules.

Anyway though this might interest a few people.


Regards,

Ian Ridley
mailto:iridley@ingenico.com.au
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   ---- File information -----------
     File:  shmem.tgz
     Date:  23 Apr 1998, 9:46
     Size:  8373 bytes.
     Type:  Unknown

shmem.tgz