use cases for mmap

Hi guys

I'm reading&learning kernel codes and have a question for mmap. Many
guys said mmap is good for sharing data between processes[0]. But how
does mmap do that?

In document, mmap is defined as:

mmap(void *addr, size_t len, int prot, int flags, int fd, off_t offset)

That addr is virtual address and different processes have different
address space. So after put a file into memory via addr$offsett, how
does another process read that data?

Btw, are there some common use cases for mmap, in application layer?

[0] http://stackoverflow.com/questions/258091/when-should-i-use-mmap-for-file-access


Thanks :)

Gareth
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