Device Drivers Concluded
Technology develops, but the ideas often remain the same. In the old ISA world, peripherals located their buffers at the “very high end of address space”--above 640 KB. Many PCI-cards now do the same, but nowadays, this is something more like the end of a 32-bit address space (like 0xF0100000).
If you want to access a buffer at these addresses, you have to use vremap() as defined in linux/mm.h to remap the same pages of this physical memory into your own virtual address space.
vremap() works a little bit like the mmap() user call in nasty, but it's much easier:
void * vremap (unsigned long offset, unsigned long size);
You just pass the start address of your buffer and its length. Remember, we always map pages; therefore offset and size have to be page length-aligned. If your buffer is smaller or does not start on a page boundary, map the whole page and try to avoid accessing invalid addresses.
I personally have not tried this, and I'm not sure if the tricks I described above on how to map buffers to user space work with PCI high memory buffers. If you want to give it a try, you definitely have to remove the “brute force” manipulation of the mem_map array, as mem_map is only for physical RAM. Try to replace the kmalloc() and kfree() stuff with the analogous vremap() calls and then perform a second remapping with do_mmap() to user space.
But as you might realize, we've come to an end of this series, and now it is up to you to boldly go where no Linuxer has gone before...
George V. Zezschwitz is a 27-year old Linuxer who enjoys late-night hacking and hates deadlines.
Fast/Flexible Linux OS Recovery
On Demand Now
In this live one-hour webinar, learn how to enhance your existing backup strategies for complete disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible full-system recovery solution for UNIX and Linux systems.
Join Linux Journal's Shawn Powers and David Huffman, President/CEO, Storix, Inc.
Free to Linux Journal readers.Register Now!
- Server Hardening
- BitTorrent Inc.'s Sync
- Download "Linux Management with Red Hat Satellite: Measuring Business Impact and ROI"
- New Container Image Standard Promises More Portable Apps
- The Humble Hacker?
- The Death of RoboVM
- The US Government and Open-Source Software
- Open-Source Project Secretly Funded by CIA
- EnterpriseDB's EDB Postgres Advanced Server and EDB Postgres Enterprise Manager
- Varnish Software's Hitch
In modern computer systems, privacy and security are mandatory. However, connections from the outside over public networks automatically imply risks. One easily available solution to avoid eavesdroppers’ attempts is SSH. But, its wide adoption during the past 21 years has made it a target for attackers, so hardening your system properly is a must.
Additionally, in highly regulated markets, you must comply with specific operational requirements, proving that you conform to standards and even that you have included new mandatory authentication methods, such as two-factor authentication. In this ebook, I discuss SSH and how to configure and manage it to guarantee that your network is safe, your data is secure and that you comply with relevant regulations.Get the Guide