Direct Memory Access in Linux

Question

I\'m trying to access physical memory directly for an embedded Linux project, but I\'m not sure how I can best designate memory for my use.

If I boot my device regul

Answer 1

Sorry to answer but not quite answer, I noticed that you have already edited the question. Please note that SO does not notify us when you edit the question. I'm giving a generic answer here, when you update the question please leave a comment, then I'll edit my answer.

Yes, you're going to need to write a module. What it comes down to is the use of kmalloc() (allocating a region in kernel space) or vmalloc() (allocating a region in userspace).

Exposing the prior is easy, exposing the latter can be a pain in the rear with the kind of interface that you are describing as needed. You noted 1.5 MB is a rough estimate of how much you actually need to reserve, is that iron clad? I.e are you comfortable taking that from kernel space? Can you adequately deal with ENOMEM or EIO from userspace (or even disk sleep)? IOW, what's going into this region?

Also, is concurrency going to be an issue with this? If so, are you going to be using a futex? If the answer to either is 'yes' (especially the latter), its likely that you'll have to bite the bullet and go with vmalloc() (or risk kernel rot from within). Also, if you are even THINKING about an ioctl() interface to the char device (especially for some ad-hoc locking idea), you really want to go with vmalloc().

Also, have you read this? Plus we aren't even touching on what grsec / selinux is going to think of this (if in use).