2.2.0 fails to build with --disable-drm

[kostadinsh]

ddcutil 2.2.0 fails to build with --disable-drm. First bad commit is https://github.com/rockowitz/ddcutil/commit/aeb0b58

ddcutil 2.2.0
        version suffix:   
        =============

        libtool version         7:0:2

        prefix:                 /usr/local
        exec_prefix:            ${prefix}
        libexecdir:             ${exec_prefix}/libexec
        bindir:                 ${exec_prefix}/bin
        libdir:                 ${exec_prefix}/lib
        datarootdir:            ${prefix}/share
        datadir:                ${datarootdir}
        docdir:                 ${datarootdir}/doc/${PACKAGE_TARNAME}
        mandir:                 ${datarootdir}/man
        includedir:             ${prefix}/include
        pkgconfigdir:           
        required_packages:       glib-2.0 >= 2.40 jansson >= 2.0

        enable_lib:             yes
        enable_install_lib_only no
        enable_build_timestamp  yes
        enable_envcmds          yes
        enable_udev             yes
        enable_usb:             yes
        enable_drm:             no
        enable_x11:             yes
        enable_asan:            no
        enable_static_functions_visible:  no

        Developer-only options:
        enable_targetbsd:       no
        enable_doxygen:         no
        enable_failsim:         no
        include_testcases:      no

        compiler:               gcc
        CFLAGS:                 -g -O2
        CPPFLAGS:               
        LDFLAGS:

In file included from drm_connector_state.h:13,
                 from base_services.c:15:
/usr/include/xf86drmMode.h:43:10: fatal error: drm.h: No such file or directory
   43 | #include <drm.h>
      |          ^~~~~~~
compilation terminated.
In file included from drm_connector_state.c:18:
/usr/include/xf86drm.h:40:10: fatal error: drm.h: No such file or directory
   40 | #include <drm.h>
      |          ^~~~~~~

[rockowitz]

Can I ask what sort of system you have without drm? While the fix for --disable-x11 was straightforward, reimplementing --disable-drm is not.

[kostadinsh]

There's nothing special about my system. We just used to have a USE flag that enabled or disabled drm before 2.2.0, but now it's gone and it's always enabled because of the above failure. Maybe you could get rid of the --enable-drm configure option altogether considering disabling it is broken, and just force the build to always use it?

[rockowitz]

configure option --disable-drm has been reimplemented. If built with configure option --disable-drm, ddcutil does not make use of DRM APIs. This does not block reading of /sys, the contents of which can be set by DRM. I don't have a true drm-less system to test against, it's possible that there are unhandled errors in that situation.

Also added is configure option --disable-watch-displays, controlling whether libddcutil watches for display connection changes. --disable-drm forces --disable-watch-displays.

[kostadinsh]

2.2.1 builds fine, but when running the test suite with make check I am getting: /usr/lib/gcc/x86_64-pc-linux-gnu/16/../../../../x86_64-pc-linux-gnu/bin/ld: ../.libs/libddcutil.so: undefined reference to 'dw_redetect_displays'

[rockowitz]

I assume that by "when running the test suite" you meant building with "make check" and did not mean executing the demo programs created by make check.

Commit 2ed9275c in branch 2.2.2-dev allows building to complete without the undefined reference error when configure option --disable-drm was specified. API function ddca_redetect_displays() returns DDCA_INVALID_OPERATION in this case. (An alternative code path through ddca_redetect_displays() is possible for the --disable-drm case, but is non-trivial and so not implemented for now.)

[rockowitz]

Note correction of the branch name in my prior comment. It is 2.2.2-dev, not 2.2.1-dev.