[erlang-questions] mmap(2) to a binary?

Scott Lystig Fritchie <>
Fri Sep 28 18:24:03 CEST 2007


>>>>> "dt" == David Terrell <> writes:

dt> In reference to the ongoing thread here and in the blogosphere, I
dt> had an idea for doing some arbitrary file I/O in convenient
dt> fashion.  What if you could call mmap() on a file and get a binary
dt> out of it that points directly to the mapped space?

It's quite easy to do, in a naive manner.  If you have a read-only
mapped region, *and* if nobody else updates the file while you've got
the region mapped, then a linked-in driver can do everything you need.
If either of those assumptions are incorrect, then a very naive driver
will violate VM internals' assumptions in a pretty spectacular way.

In the general case, I think you'd need to have two basic ops:

    * map a region
    * given a region, starting offset, and length, copy length
      bytes into a new binary (so that its contents can't change)

In the general case, there are other things you'd also need or want,
of course: unmap a region, tie mapped regions to the process so that
the regions are unmapped if the owner process dies, ...

-Scott



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