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?

The following looks correct: mmap.mmap(file_no, length, access=mmap.ACCESS_COPY, offset=offset). What happens when you try it? — NPE
– NPE, Commented Jun 7, 2012 at 14:14
Updated question to show you. just an invalid argument error (and yes, it works if I take away the offset=2) — joslinm
– joslinm, Commented Jun 7, 2012 at 14:16

phihag · Accepted Answer · 2012-06-07 14:20:29Z

6

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

answered Jun 7, 2012 at 14:20

phihag

289k75 gold badges475 silver badges489 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

joslinm Over a year ago

Right, that makes sense. I confused myself when m = mmap.mmap(f.fileno(), 4, mmap.MAP_SHARED, mmap.PROT_READ | mmap.PROT_WRITE, 2) seemed to work. Thanks.

luke14free · Accepted Answer · 2012-06-07 14:23:36Z

1

try with:

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

answered Jun 7, 2012 at 14:23

luke14free

2,5491 gold badge18 silver badges25 bronze badges

Collectives™ on Stack Overflow

How do I specify offset and access in mmap?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related