torture: Make kvm-test-1-run-qemu.sh apply affinity

This commit causes the kvm-test-1-run-qemu.sh script to check the
TORTURE_AFFINITY environment variable and to add "taskset" commands to
the qemu-cmd file.  The first "taskset" command is applied only if the
TORTURE_AFFINITY environment variable is a non-empty string, and this
command pins the current scenario's guest OS to the specified CPUs.
The second "taskset" command reports the guest OS's affinity in a new
"qemu-affinity" file.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/kvm-test-1-run-qemu.sh

@@ -39,9 +39,16 @@ echo ' ---' `date`: Starting kernel, PID $$
 grep '^#' $resdir/qemu-cmd | sed -e 's/^# //' > $T/qemu-cmd-settings
 . $T/qemu-cmd-settings
 
-# Decorate qemu-cmd with redirection, backgrounding, and PID capture
-sed -e 's/^[^#].*$/& 2>\&1 \&/' < $resdir/qemu-cmd > $T/qemu-cmd
-echo 'echo $! > $resdir/qemu_pid' >> $T/qemu-cmd
+# Decorate qemu-cmd with affinity, redirection, backgrounding, and PID capture
+taskset_command=
+if test -n "$TORTURE_AFFINITY"
+then
+	taskset_command="taskset -c $TORTURE_AFFINITY "
+fi
+sed -e 's/^[^#].*$/'"$taskset_command"'& 2>\&1 \&/' < $resdir/qemu-cmd > $T/qemu-cmd
+echo 'qemu_pid=$!' >> $T/qemu-cmd
+echo 'echo $qemu_pid > $resdir/qemu_pid' >> $T/qemu-cmd
+echo 'taskset -c -p $qemu_pid > $resdir/qemu-affinity' >> $T/qemu-cmd
 
 # In case qemu refuses to run...
 echo "NOTE: $QEMU either did not run or was interactive" > $resdir/console.log