===== Driver API tracing =====


==== Enabling ====

Since 2.6.32 mac80211 includes a tracing framework, and since 3.2 it is always enabled if possible (if EVENT_TRACING is enabled in the kernel.) 

To be able to use it on kernels before 3.2, enable <code>CONFIG_MAC80211_DRIVER_API_TRACER</code> (requires tracing and <code>CONFIG_MAC80211_DEBUG_MENU</code>). 


==== Using trace-cmd ====

The easiest way to give a trace to other people is to use trace-cmd, see also [[https://lwn.net/Articles/410200/|https://lwn.net/Articles/410200/]]. To record a trace with trace-cmd, use 
<code>trace-cmd record -e mac80211</code>
This will record until you hit Ctrl-C to abort. The result is stored in a file "trace.dat" which you can send around for analysis. You should compress it before sending it to other people since it is relatively large but compresses well. 

To analyse a file, use 
<code>trace-cmd report -i trace.dat | less</code>

==== cfg80211 and wpasupplicant ====

Both cfg80211 and wpasupplicant have tracing support. Use '-e cfg80211' with trace-cmd to enable all cfg80211 tracing points. For wpasupplicant enable CONFIG_DEBUG_LINUX_TRACING build config and use -T switch to get log messages sent to the tracing framework. 


==== Driver tracing ====

In addition to mac80211, some drivers include tracing as well. 


=== iwlwifi ===

For iwlwifi, set the <code>IWLWIFI_DEVICE_TRACING</code> Kconfig option. You can then get new trace subsystems: 

  ; iwlwifi  : the commands exchanged between driver and device 
  ; iwlwifi_io  : the device IO accesses and interrupt information 
  ; iwlwifi_msg  : all debug messages from the driver 
  ; iwlwifi_ucode  : uCode events (not sure they're useful today) 
  ; iwlwifi_data  : data for TX/RX frames 
Recommended: 
<code>trace-cmd record -e mac80211 -e mac80211_msg -e iwlwifi -e iwlwifi_msg -e iwlwifi_data</code>