Merge branches 'tracing/ftrace' and 'linus' into tracing/core

[linux-2.6-omap-h63xx.git] / Documentation / sysrq.txt

diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 10a0263ebb3f01e832c7827cc75d7fe54b341a6f..535aeb936dbce90acda756ada8988f9dd43a88a2 100644 (file)
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -1,6 +1,5 @@
 Linux Magic System Request Key Hacks
 Documentation for sysrq.c
-Last update: 2007-AUG-04
 
 *  What is the magic SysRq key?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -114,6 +113,8 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 
 'x'    - Used by xmon interface on ppc/powerpc platforms.
 
+'z'    - Dump the ftrace buffer
+
 '0'-'9' - Sets the console log level, controlling which kernel messages
           will be printed to your console. ('0', for example would make
           it so that only emergency messages like PANICs or OOPSes would
@@ -211,6 +212,24 @@ within a function called by handle_sysrq, you must be aware that you are in
 a lock (you are also in an interrupt handler, which means don't sleep!), so
 you must call __handle_sysrq_nolock instead.
 
+*  When I hit a SysRq key combination only the header appears on the console?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Sysrq output is subject to the same console loglevel control as all
+other console output.  This means that if the kernel was booted 'quiet'
+as is common on distro kernels the output may not appear on the actual
+console, even though it will appear in the dmesg buffer, and be accessible
+via the dmesg command and to the consumers of /proc/kmsg.  As a specific
+exception the header line from the sysrq command is passed to all console
+consumers as if the current loglevel was maximum.  If only the header
+is emitted it is almost certain that the kernel loglevel is too low.
+Should you require the output on the console channel then you will need
+to temporarily up the console loglevel using alt-sysrq-8 or:
+
+    echo 8 > /proc/sysrq-trigger
+
+Remember to return the loglevel to normal after triggering the sysrq
+command you are interested in.
+
 *  I have more questions, who can I ask?
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 And I'll answer any questions about the registration system you got, also