tracing: Add division and multiplication support for hist triggers

Adds basic support for division and multiplication operations for
hist trigger variable expressions.

For simplicity this patch only supports, division and multiplication
for a single operation expression (e.g. x=$a/$b), as currently
expressions are always evaluated right to left. This can lead to some
incorrect results:

	e.g. echo 'hist:keys=common_pid:x=8-4-2' >> event/trigger

	     8-4-2 should evaluate to 2 i.e. (8-4)-2
	     but currently x evaluate to  6 i.e. 8-(4-2)

Multiplication and division in sub-expressions will work correctly, once
correct operator precedence support is added (See next patch in this
series).

For the undefined case of division by 0, the histogram expression
evaluates to (u64)(-1). Since this cannot be detected when the
expression is created, it is the responsibility of the user to be
aware and account for this possibility.

Examples:
	echo 'hist:keys=common_pid:a=8,b=4,x=$a/$b' \
                   >> event/trigger

	echo 'hist:keys=common_pid:y=5*$b' \
                   >> event/trigger

Link: https://lkml.kernel.org/r/20211025200852.3002369-3-kaleshsingh@google.com

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

0 files changed, 0 insertions, 0 deletions