multiprocess: move feature to meson_options.txt

While at it, improve the description of the feature in the summary and
help message.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -463,7 +463,7 @@ skip_meson=no
 gettext="auto"
 fuse="auto"
 fuse_lseek="auto"
-multiprocess="no"
+multiprocess="auto"
 
 malloc_trim="auto"
 
@@ -798,7 +798,6 @@ Linux)
   linux="yes"
   linux_user="yes"
   vhost_user=${default_feature:-yes}
-  multiprocess=${default_feature:-yes}
 ;;
 esac
 
@@ -1558,9 +1557,9 @@ for opt do
   ;;
   --disable-fuse-lseek) fuse_lseek="disabled"
   ;;
-  --enable-multiprocess) multiprocess="yes"
+  --enable-multiprocess) multiprocess="enabled"
   ;;
-  --disable-multiprocess) multiprocess="no"
+  --disable-multiprocess) multiprocess="disabled"
   ;;
   *)
       echo "ERROR: unknown option $opt"
@@ -1914,7 +1913,7 @@ disabled with --disable-FEATURE, default is enabled if available
   libdaxctl       libdaxctl support
   fuse            FUSE block device export
   fuse-lseek      SEEK_HOLE/SEEK_DATA support for FUSE exports
-  multiprocess    Multiprocess QEMU support
+  multiprocess    Out of process device emulation support
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -6089,9 +6088,6 @@ fi
 if test "$have_mlockall" = "yes" ; then
   echo "HAVE_MLOCKALL=y" >> $config_host_mak
 fi
-if test "$multiprocess" = "yes" ; then
-  echo "CONFIG_MULTIPROCESS_ALLOWED=y" >> $config_host_mak
-fi
 if test "$fuzzing" = "yes" ; then
   # If LIB_FUZZING_ENGINE is set, assume we are running on OSS-Fuzz, and the
   # needed CFLAGS have already been provided
@@ -6434,7 +6430,7 @@ NINJA=$ninja $meson setup \
         -Dzstd=$zstd -Dseccomp=$seccomp -Dvirtfs=$virtfs -Dcap_ng=$cap_ng \
         -Dattr=$attr -Ddefault_devices=$default_devices \
         -Ddocs=$docs -Dsphinx_build=$sphinx_build -Dinstall_blobs=$blobs \
-        -Dvhost_user_blk_server=$vhost_user_blk_server \
+        -Dvhost_user_blk_server=$vhost_user_blk_server -Dmultiprocess=$multiprocess \
         -Dfuse=$fuse -Dfuse_lseek=$fuse_lseek -Dguest_agent_msi=$guest_agent_msi \
         $(if test "$default_features" = no; then echo "-Dauto_features=disabled"; fi) \
 	-Dtcg_interpreter=$tcg_interpreter \

meson.build

@@ -157,6 +157,11 @@ if targetos != 'linux' and get_option('mpath').enabled()
   error('Multipath is supported only on Linux')
 endif
 
+if targetos != 'linux' and get_option('multiprocess').enabled()
+  error('Multiprocess QEMU is supported only on Linux')
+endif
+multiprocess_allowed = targetos == 'linux' and not get_option('multiprocess').disabled()
+
 m = cc.find_library('m', required: false)
 util = cc.find_library('util', required: false)
 winmm = []
@@ -1228,7 +1233,7 @@ host_kconfig = \
   (have_virtfs ? ['CONFIG_VIRTFS=y'] : []) + \
   ('CONFIG_LINUX' in config_host ? ['CONFIG_LINUX=y'] : []) + \
   ('CONFIG_PVRDMA' in config_host ? ['CONFIG_PVRDMA=y'] : []) + \
-  ('CONFIG_MULTIPROCESS_ALLOWED' in config_host ? ['CONFIG_MULTIPROCESS_ALLOWED=y'] : [])
+  (multiprocess_allowed ? ['CONFIG_MULTIPROCESS_ALLOWED=y'] : [])
 
 ignored = [ 'TARGET_XML_FILES', 'TARGET_ABI_DIR', 'TARGET_ARCH' ]
 
@@ -2538,6 +2543,7 @@ endif
 summary_info += {'target list':       ' '.join(target_dirs)}
 if have_system
   summary_info += {'default devices':   get_option('default_devices')}
+  summary_info += {'out of process emulation': multiprocess_allowed}
 endif
 summary(summary_info, bool_yn: true, section: 'Targets and accelerators')
 
@@ -2658,7 +2664,6 @@ summary_info += {'libpmem support':   config_host.has_key('CONFIG_LIBPMEM')}
 summary_info += {'libdaxctl support': config_host.has_key('CONFIG_LIBDAXCTL')}
 summary_info += {'libudev':           libudev.found()}
 summary_info += {'FUSE lseek':        fuse_lseek.found()}
-summary_info += {'Multiprocess QEMU': config_host.has_key('CONFIG_MULTIPROCESS_ALLOWED')}
 summary(summary_info, bool_yn: true, section: 'Dependencies')
 
 if not supported_cpus.contains(cpu)

meson_options.txt

@@ -45,6 +45,8 @@ option('cfi', type: 'boolean', value: 'false',
        description: 'Control-Flow Integrity (CFI)')
 option('cfi_debug', type: 'boolean', value: 'false',
        description: 'Verbose errors in case of CFI violation')
+option('multiprocess', type: 'feature', value: 'auto',
+       description: 'Out of process device emulation support')
 
 option('attr', type : 'feature', value : 'auto',
        description: 'attr/xattr support')