[PATCH] Fix 'Invalid argument' error with 'opcontrol --start' in Timer mode

[Maynard J. <may...@us...>]

Fix 'Invalid argument' error with 'opcontrol --start' in Timer mode

When a processor type does not support oprofile event-based profiling,
the oprofile kernel driver writes "timer" to the /dev/oprofile/cpu_type
file.  Usually (perhaps "always"), the architecture-specific oprofile
kernel driver does not set up the standard oprofile function pointers
that are defined in 'struct oprofile_operations oprofile_ops'.  One of
those function pointers is 'oprofile_ops.backtrace'.  When opcontrol
"--start" option is being executed, one of the actions taken is to write
the CALLGRAPH value from the daemonrc file to /dev/oprofile/backtrace_depth.
The kernel driver's filesystem function defined to respond to writes to this
file is drivers/oprofile/oprofile_files.c:depth_write().  In that function,
if 'oprofile_ops.backtrace' is not set, it returns -EINVAL, resulting in
the following opcontrol error:
   opcontrol: line 1172: echo: write error: Invalid argument

This patch detects when the system is in timer mode and handles this error
appropriately -- if simply writing '0' to backtrace_depth, the error is
ignored; otherwise, print a message that call graph is not supported on
this system in TIMER mode.

Signed-off-by: Maynard Johnson <may...@us...>
---
 utils/opcontrol |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/utils/opcontrol b/utils/opcontrol
index 038e0db..20c6c6a 100644
--- a/utils/opcontrol
+++ b/utils/opcontrol
@@ -1173,7 +1173,18 @@ do_setup()
 set_param()
 {
 	if test "$KERNEL_SUPPORT" = "yes"; then
-		echo $2 >$MOUNT/$1
+		if test "$IS_TIMER" = 1 -a "$1" = "backtrace_depth"; then
+			echo "Writing $2 to $MOUNT/$1"
+			echo $2 >$MOUNT/$1 > /dev/null
+			if test "$2" -ne 0; then
+				result=`cat $MOUNT/$1`
+				if test "$result" -ne "$2"; then
+					echo "Callgraph profiling not supported on this system in Timer mode"
+				fi
+			fi
+		else
+			echo $2 >$MOUNT/$1
+		fi
 	else
 		$SYSCTL -w dev.oprofile.$1=$2
 	fi
-- 
1.7.1