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.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- The Firebird Project's Firebird Relational Database
- Stunnel Security for Oracle
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Parsing an RSS News Feed with a Bash Script
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide