Standalone krnlmon build

[ffoulkes]

This CL makes it possible to build the Kernel Monitor from its own cmake listfile, independently (more or less) of P4 Control Plane.

For example:

export SDE_INSTALL=<es2k-sde-dir>
cd krnlmon/krnlmon

cmake -B build \
    -DSAI_SOURCE_DIR=../SAI \
    -DCMAKE_MODULE_PATH=../../cmake \
    -DCMAKE_INSTALL_PREFIX=install \
    -DTDI_TARGET=es2k

cmake --build build -j4

The chief awkwardness is making the SelectTdiTarget, FindDpdkDriver, and FindTofinoDriver modules available to the standalone build. The long-term solution is probably to create a separate repository that contains the common modules and reference it through a cmake variable in any project that requires them.

Reasons for supporting standalone build:

• Makes the Kernel Monitor a component in its own right, and hence easier to reuse the code in other projects.
• Allows us to do test builds and run unit tests on the component itself (e.g., when a PR is created to update krnlmon).
• Improves our ability to do incremental builds of larger systems (something we very much want to do for MEV).
• Allows us to run analyzers such as include-what-you-use on Kernel Monitor (Add support for include-what-you-use #61).

The effort has led to additional error checks and some improvements in the krnlmon build.

[ffoulkes]

An even cooler way to do standalone builds:

es2k-config.cmake

set(DEPEND_INSTALL_DIR "/opt/deps" CACHE PATH
    "config: Dependencies install directory")

set(SDE_INSTALL_DIR "/opt/p4sde/mev" CACHE PATH
    "config: SDE install directory")

get_filename_component(_path "${CMAKE_SOURCE_DIR}/../SAI" REALPATH)
set(SAI_SOURCE_DIR "${_path}" CACHE PATH "config: SAI source directory")

# P4 Control Plane cmake modules
get_filename_component(_path "${CMAKE_SOURCE_DIR}/../../cmake" REALPATH)
set(CMAKE_MODULE_PATH "${_path}" CACHE PATH "" FORCE)

set(CMAKE_INSTALL_PREFIX "${CMAKE_SOURCE_DIR}/install" CACHE PATH "")

set(TDI_TARGET "es2k" CACHE STRING "config: TDI target type")

unset(_path)

Usage

cmake -B build -C es2k-config.cmake
cmake --build build -j4

[5abeel]

One question on the PROJECT VERSION. Rest LGTM

[5abeel]

Are we (planning to) giving each submodule a version number?

[ffoulkes]

I'm leaning in favor of versioning cmake projects that are, or may be considered to be, discrete packages or components.

krnlmon already had a version number of sorts, defined by the VERSION variable later in this file and substituted into the libkrnlmon pkg-config file.

This CL moves the definition to the cmake project() command, bumps the version number from 1.0 to 2.0, and replaces the VERSION variable with PROJECT_VERSION when creating the pkg-config file.

CMake defines PROJECT_VERSION when you specify project(VERSION x.x).