Re: Threads and the LDT (Intel-specific)?

[Jeff Dike <jdike@karaya.com>]

smlong@teleport.com said:
> I'm trying to do something a bit unorthodox: I want to share the
> address space between threads, but I want a certain region of the
> address space to be writeable only for a particular thread -- for all
> other threads this region is read-only. 

UML does this in a somewhat portable (but strange) way.  Threads don't share 
address spaces, as far as the OS is concerned, but the areas where the 
executable is mapped in are copied to a file, those areas are mapped out, and 
the files mapped shared in their place.  This happens once, in the first 
thread, and all subsequent threads get the executable mapped shared 
automatically, even though they are separate processes and separate address 
spaces from the point of view of the kernel.

So, once this is set up, a thread just makes an area read-write (or readonly) 
and that mapping is private.

				Jeff