Interprocess shared memory .... but file backed?

[Christopher Quinn <cq@htec.demon.co.uk>]

Hello,

I know that a combination of mmap/shmem can be used to 
achieve interprocess shared memory (notably Ralf 
Engelschall's MM library).
However as far as I can tell this is anonymous memory only.
Are there any options if one initially maps a disk file via 
mmap (in particular MAP_PRIVATE) for sharing that vm, such 
that any access by a member of the sharing process group 
will fault in the relevant file data page after which writes 
to it are seen by all?

Of course clone(2) will give the necessary sharing of page 
tables but my ideal is for sharing only of specified areas 
of vm, not everything.

Anyone know of a way of doing this?

Thanks,
Chris Quinn

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