build: add --enable/--disable-libudev

Initially, libudev detection was bundled with --enable-mpath because
qemu-pr-helper was the only user of libudev.  Recently however the USB
U2F emulation has also started using libudev, so add a separate
option.  This also allows 1) disabling libudev if desired for static
builds and 2) for non-static builds, requiring libudev even if
multipath support is undesirable.

The multipath test is adjusted, because it is now possible to enter it
with configurations that should fail, such as --static --enable-mpath
--disable-libudev.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -303,6 +303,7 @@ netmap="no"
 sdl="auto"
 sdl_image="auto"
 virtfs=""
+libudev="auto"
 mpath="auto"
 vnc="enabled"
 sparse="auto"
@@ -1002,6 +1003,10 @@ for opt do
   ;;
   --enable-virtfs) virtfs="yes"
   ;;
+  --disable-libudev) libudev="disabled"
+  ;;
+  --enable-libudev) libudev="enabled"
+  ;;
   --disable-mpath) mpath="disabled"
   ;;
   --enable-mpath) mpath="enabled"
@@ -1759,6 +1764,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   vnc-png         PNG compression for VNC server
   cocoa           Cocoa UI (Mac OS X only)
   virtfs          VirtFS
+  libudev         Use libudev to enumerate host devices
   mpath           Multipath persistent reservation passthrough
   xen             xen backend driver support
   xen-pci-passthrough    PCI passthrough support for Xen
@@ -7060,7 +7066,7 @@ NINJA=$ninja $meson setup \
         -Dvnc=$vnc -Dvnc_sasl=$vnc_sasl -Dvnc_jpeg=$vnc_jpeg -Dvnc_png=$vnc_png \
         -Dgettext=$gettext -Dxkbcommon=$xkbcommon -Du2f=$u2f \
         -Dcapstone=$capstone -Dslirp=$slirp -Dfdt=$fdt \
-        -Diconv=$iconv -Dcurses=$curses \
+        -Diconv=$iconv -Dcurses=$curses -Dlibudev=$libudev\
         $cross_arg \
         "$PWD" "$source_path"
 

meson.build

@@ -380,10 +380,11 @@ endif
 libudev = not_found
 if targetos == 'linux' and (have_system or have_tools)
   libudev = dependency('libudev',
-                       required: get_option('mpath').enabled(),
+                       required: get_option('libudev'),
                        static: enable_static)
 endif
 
+mpathlibs = [libudev]
 mpathpersist = not_found
 mpathpersist_new_api = false
 if targetos == 'linux' and have_tools and not get_option('mpath').disabled()
@@ -414,35 +415,40 @@ if targetos == 'linux' and have_tools and not get_option('mpath').disabled()
           mpath_lib_init(udev);
           return 0;
       }'''
-  mpathlibs = [libudev]
-  if enable_static
-    mpathlibs += cc.find_library('devmapper',
-                                   required: get_option('mpath'),
-                                   static: enable_static)
-  endif
-  mpathlibs += cc.find_library('multipath',
-                               required: get_option('mpath'),
-                               static: enable_static)
-  mpathlibs += cc.find_library('mpathpersist',
-                               required: get_option('mpath'),
-                               static: enable_static)
-  foreach lib: mpathlibs
-    if not lib.found()
-      mpathlibs = []
-      break
+  libmpathpersist = cc.find_library('mpathpersist',
+                                    required: get_option('mpath'),
+                                    static: enable_static)
+  if libmpathpersist.found()
+    mpathlibs += libmpathpersist
+    if enable_static
+      mpathlibs += cc.find_library('devmapper',
+                                     required: get_option('mpath'),
+                                     static: enable_static)
     endif
-  endforeach
-  if mpathlibs.length() > 0
-    if cc.links(mpath_test_source_new, dependencies: mpathlibs)
+    mpathlibs += cc.find_library('multipath',
+                                 required: get_option('mpath'),
+                                 static: enable_static)
+    foreach lib: mpathlibs
+      if not lib.found()
+        mpathlibs = []
+        break
+      endif
+    endforeach
+    if mpathlibs.length() == 0
+      msg = 'Dependencies missing for libmpathpersist'
+    elif cc.links(mpath_test_source_new, dependencies: mpathlibs)
       mpathpersist = declare_dependency(dependencies: mpathlibs)
       mpathpersist_new_api = true
     elif cc.links(mpath_test_source_old, dependencies: mpathlibs)
       mpathpersist = declare_dependency(dependencies: mpathlibs)
     else
+      msg = 'Cannot detect libmpathpersist API'
+    endif
+    if not mpathpersist.found()
       if get_option('mpath').enabled()
-        error('Cannot detect libmpathpersist API')
+        error(msg)
       else
-        warning('Cannot detect libmpathpersist API, disabling')
+        warning(msg + ', disabling')
       endif
     endif
   endif

meson_options.txt

@@ -36,6 +36,8 @@ option('iconv', type : 'feature', value : 'auto',
        description: 'Font glyph conversion support')
 option('curses', type : 'feature', value : 'auto',
        description: 'curses UI')
+option('libudev', type : 'feature', value : 'auto',
+       description: 'Use libudev to enumerate host devices')
 option('sdl', type : 'feature', value : 'auto',
        description: 'SDL user interface')
 option('sdl_image', type : 'feature', value : 'auto',