Snooping the USB Data Stream
to log the control request information. After the read has completed, I add the following lines to log the actual data read from the device:
printk("control read: data "); for (j = 0; j < ctrl.wLength; ++j) printk("%02x ", ctrl.data[j]); printk("\n");
After doing much the same modification to the write section of the if statement, I build, reload the usbcore modules and verify that I now can log all control messages to and from the device. The messages returned are:
CONTROL control read: bRequest=06 bRrequestType=80 wValue=0300 wIndex=0000 control read: data 00 00 61 63
Day 6: Looking at the modifications I have made to the kernel code, I think this work might be something other users might like to have. So, it is time to clean up the code to a state that the USB maintainer might accept for the main kernel source tree.
First, I recognized that the calls to printk() are incorrect. All printk() calls must be accompanied by a proper logging level. These logging levels are added to printk calls by pre-appending the proper KERN_ values to the message. The file include/linux/kernel.h contains the following valid values that must be used:
#define KERN_EMERG "<0>" /* system is unusable */ #define KERN_ALERT "<1>" /* action must be taken immediately */ #define KERN_CRIT "<2>" /* critical conditions */ #define KERN_ERR "<3>" /* error conditions */ #define KERN_WARNING "<4>" /* warning conditions */ #define KERN_NOTICE "<5>" /* normal but significant condition */ #define KERN_INFO "<6>" /* informational */ #define KERN_DEBUG "<7>" /* debug-level messages */
So, I change the printk calls in the usbfs_ioctl() function from:
Now the kernel janitors should not complain about improper printk() usage.
In looking further at the logging messages, however, it is hard to determine for what exact device the message is being logged. More information needs to be added to the printk() calls. Luckily, some macros already in the include/linux/device.h file can help us. They are the dev_printk() macro and its helper macros, dev_dbg(), dev_warn(), dev_info() and dev_err(). These macros all need an additional pointer to a struct device variable, which allows them to print out the unique device ID for the message. So I change the printk() calls again to look like this:
Then the control message printk() calls are changed to:
dev_info(&dev->dev, "control read: " "bRequest=%02x bRrequestType=%02x " "wValue=%04x wIndex=%04x\n", ctrl.bRequest, ctrl.bRequestType, ctrl.wValue, ctrl.wIndex); dev_info(&dev->dev, "control read: data "); for (j = 0; j < ctrl.wLength; ++j) printk("%02x ", ctrl.data[j]); printk("\n");
The printk calls that dump the data do not need to be changed, as they still are printing on the same line as the call to dev_info().
Now the log messages are much more informative, looking like the following:
usb 1-1: CONTROL usb 1-1: control read: bRequest=06 bRrequestType=80 wValue=0300 wIndex=0000 usb 1-1: control read: data 00 00 61 63
I can determine exactly what USB device is being talked to, which helps me weed out the messages for devices I do not care about.
Day 7: Oops, I now realize that if I expect this kernel change to be accepted by the community, I had better not always generate these messages. Otherwise, everyone would have their system logs overflowing with messages they do not care about. How to log messages only when asked?
I first look into making a new kernel build configuration option. A simple modification of the drivers/usb/core/Kconfig file adding a new option is simple, but in examining the required code changes, I soon realize that wrapping all of the new logging statements in a #ifdef CONFIG_USBFS_LOGGING statement would make the USB maintainer reject my kernel patch. #ifdef is not generally allowed within kernel code, as it cuts down on readability and makes maintaining the code over time almost impossible.
Instead, I look at making an option that can be changed at runtime. I add the following lines of code to the devio.c file:
static int usbfs_snoop = 0; module_param (usbfs_snoop, bool, S_IRUGO | S_IWUSR); MODULE_PARM_DESC (usbfs_snoop, "true to log all usbfs traffic");
This adds a new module parameter to the main usbcore module called usbfs_snoop. This can be seen after building the code by running the modinfo program:
$ modinfo usbcore license: GPL parm: blinkenlights:true to cycle leds on hubs parm: usbfs_snoop:true to log all usbfs traffic
By loading the module with the following line:
modprobe usbcore usbfs_snoop=1
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.
Free to Linux Journal readers.View Now!
|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|
- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- Non-Linux FOSS: Caffeine!
- My +1 Sword of Productivity
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
- SuperTuxKart 0.9.2 Released
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