meson: Add build-lsfd option and make rt dependency optional

A dependency on the rt library is unnecessarily required when checking
for the clock_gettime and timer_create functions.
This causes the build to fail if the rt library is not found.
This should not fail the build as rt is only required for the checks.
Additionally, the lsfd executable and some tests require rt.
There is currently no option to toggle building lsfd.

This PR makes it possible to build without the rt library.
Function checks no longer require rt for the build.
The function checks for the rt library only run when rt is available.
This PR adds an option to allow building without lsfd.
This makes it possible to build without the executable that requires rt.
To not require rt for the test, a additional check has been added.
The effected tests won't be built unless rt has been found.

Signed-off-by: Jordan Williams <jordan@jwillikers.com>

2 files changed, 22 insertions, 13 deletions

diff --git a/meson.build b/meson.build
index 91726da86d..9ead241ef9 100644
--- a/meson.build
+++ b/meson.build
@@ -731,9 +731,12 @@ endif
 realtime_libs = []
 have = cc.has_function('clock_gettime')
 if not have
-  realtime_libs += cc.find_library('rt', required : true)
-  have = cc.has_function('clock_gettime',
-                         dependencies : realtime_libs)
+  lib_rt = cc.find_library('rt', required : false)
+  if lib_rt.found()
+    realtime_libs += lib_rt
+    have = cc.has_function('clock_gettime',
+                          dependencies : realtime_libs)
+  endif
 endif
 conf.set('HAVE_CLOCK_GETTIME', have ? 1 : false)
 
@@ -741,9 +744,12 @@ thread_libs = dependency('threads')
 
 have = cc.has_function('timer_create')
 if not have
-  realtime_libs = [cc.find_library('rt', required : true)]
-  have = cc.has_function('timer_create',
-                         dependencies : realtime_libs)
+  lib_rt = cc.find_library('rt', required : false)
+  if lib_rt.found()
+    realtime_libs = [lib_rt]
+    have = cc.has_function('timer_create',
+                           dependencies : realtime_libs)
+  endif
   if not have
     realtime_libs += thread_libs
     have = cc.has_function('timer_create',
@@ -2711,19 +2717,20 @@ errnos_h = custom_target('errnos.h',
   command : ['tools/all_errnos', cc.cmd_array(), get_option('c_args')],
 )
 
-mq_libs = []
-mq_libs += cc.find_library('rt', required : true)
+lib_rt = cc.find_library('rt', required : get_option('build-lsfd'))
 
+opt = not get_option('build-lsfd').disabled()
 exe = executable(
   'lsfd',
   lsfd_sources, errnos_h,
   include_directories : includes,
   link_with : [lib_common,
                lib_smartcols],
-  dependencies : mq_libs,
+  dependencies : [lib_rt],
   install_dir : usrbin_exec_dir,
-  install : true)
-if not is_disabler(exe)
+  install : opt,
+  build_by_default : opt)
+if opt and not is_disabler(exe)
   exes += exe
   manadocs += ['misc-utils/lsfd.1.adoc']
 endif
@@ -3499,14 +3506,14 @@ exe = executable(
   build_by_default: program_tests)
 exes += exe
 
-if LINUX
+if LINUX and lib_rt.found()
   exe = executable(
     'test_mkfds',
     'tests/helpers/test_mkfds.c',
     'tests/helpers/test_mkfds.h',
     'tests/helpers/test_mkfds_ppoll.c',
     include_directories : includes,
-    dependencies : mq_libs,
+    dependencies : [lib_rt],
     build_by_default: program_tests)
   exes += exe
 endif
diff --git a/meson_options.txt b/meson_options.txt
index 7b8cf3f35f..8eb6dd9055 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -101,6 +101,8 @@ option('build-cal', type : 'feature',
        description : 'build cal')
 option('build-logger', type : 'feature',
        description : 'build logger')
+option('build-lsfd', type : 'feature',
+       description : 'build lsfd')
 option('build-switch_root', type : 'feature',
        description : 'switch_root')
 option('build-pivot_root', type : 'feature',