Linux drivers do not use the printk function directly. They use, in order of preference, subsystem-specific messages (such as netdev or v4l) or the dev_* and pr_* family of functions. The latter are described in the following table:
|
Device message |
Generic message |
Printk symbol |
|
dev_emerg |
pr_emerg |
KERN_EMERG |
|
dev_alert |
pr_alert |
KERN_ALERT |
|
dev_crit |
pr_crit |
KERN_CRIT |
|
dev_err |
pr_err |
KERN_ERR |
|
dev_warn |
pr_warn |
KERN_WARNING |
|
dev_notice |
pr_notice |
KERN_NOTICE |
|
dev_info |
pr_info |
KERN_INFO |
|
dev_dbg |
pr_debug |
KERN_DEBUG |
To enable the debug messages within a driver, you may do either of the following:
- Define DEBUG in a macro before any other header file in your driver source, as follows:
#define DEBUG
Of course, the kernel needs to be recompiled and reprogrammed for the define above to take effect.
- Use the dynamic debug kernel feature, which allows to control debug statements at runtime. You can then enable/disable all dev_dbg and pr_debug debug messages with granularity through debugfs.