How do I specify offset and access in mmap?

Question

Given mmap's constructor declaration:

class mmap.mmap(fileno, length[, flags[, prot[, access[, offset]]]])

How do I specify both access & offset?

The documentation states:

access may be specified in lieu of flags and prot as an optional keyword parameter. It is an error to specify both flags, prot and access. See the description of access above for information on how to use this parameter.

So I've tried to do things like

• mmap.mmap(file_no, length, offset, access=mmap.ACCESS_COPY)

• mmap.mmap(file_no, length, access=mmap.ACCESS_COPY, offset=offset)

  m = mmap.mmap(f.fileno(), 4, access=mmap.ACCESS_COPY, offset=2)
  Traceback (most recent call last):
  File "", line 1, in mmap.error: [Errno 22] Invalid argument

• mmap.mmap(file_no, length, mmap.ACCESS_COPY, offset)

But I can't get it to work. Why is this confusing me so much?

Answer 1

This error is unrelated to access. As documented, the offset just must be a multiple of mmap.PAGESIZE or mmap.ALLOCATIONGRANULARITY.

Answer 2

try with:

m = mmap.mmap(f.fileno(), 4, access=mmap.ACCESS_COPY, offset=2 * mmap.ALLOCATIONGRANULARITY)