configure: add --without-default-features

By default QEMU enables a lot of features if it can probe and find the
support libraries. It also enables a bunch of features by default.
This patch adds the ability to build --without-default-features which
can be paired with a --without-default-devices for a barely functional
build.

The main use case for this is testing our build assumptions and for
minimising the amount of stuff you build if you just want to test a
particular feature on your relatively slow emulated test system. On
it's own I go from:

  $ ls -lh qemu-system-aarch64
  -rwxr-xr-x 1 alex alex 120M Dec 10 12:45 qemu-system-aarch64*
  $ ldd qemu-system-aarch64 | wc -l
  170

to:

  $ ls -lh qemu-aarch64
  -rwxr-xr-x 1 alex alex 43M Dec 10 12:41 qemu-aarch64*
  $ ldd qemu-system-aarch64 | wc -l
  57

which is still able to run my default Debian ARM64 machine with a lot
less fat involved.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Thomas Huth <thuth@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20201210190417.31673-5-alex.bennee@linaro.org>

configure

@@ -293,8 +293,19 @@ unset target_list_exclude
 # Distributions want to ensure that several features are compiled in, and it
 # is impossible without a --enable-foo that exits if a feature is not found.
 
-brlapi=""
+default_feature=""
-curl=""
+# parse CC options second
+for opt do
+  optarg=$(expr "x$opt" : 'x[^=]*=\(.*\)')
+  case "$opt" in
+      --without-default-features)
+          default_feature="no"
+  ;;
+  esac
+done
+
+brlapi="$default_feature"
+curl="$default_feature"
 iconv="auto"
 curses="auto"
 docs="auto"
@@ -303,52 +314,52 @@ netmap="no"
 sdl="auto"
 sdl_image="auto"
 virtiofsd="auto"
-virtfs=""
+virtfs="$default_feature"
 libudev="auto"
 mpath="auto"
 vnc="enabled"
 sparse="auto"
-vde=""
+vde="$default_feature"
 vnc_sasl="auto"
 vnc_jpeg="auto"
 vnc_png="auto"
 xkbcommon="auto"
-xen=""
+xen="$default_feature"
-xen_ctrl_version=""
+xen_ctrl_version="$default_feature"
 xen_pci_passthrough="auto"
-linux_aio=""
+linux_aio="$default_feature"
-linux_io_uring=""
+linux_io_uring="$default_feature"
-cap_ng=""
+cap_ng="$default_feature"
-attr=""
+attr="$default_feature"
-libattr=""
+libattr="$default_feature"
-xfs=""
+xfs="$default_feature"
 tcg="enabled"
-membarrier=""
+membarrier="$default_feature"
-vhost_net=""
+vhost_net="$default_feature"
-vhost_crypto=""
+vhost_crypto="$default_feature"
-vhost_scsi=""
+vhost_scsi="$default_feature"
-vhost_vsock=""
+vhost_vsock="$default_feature"
 vhost_user="no"
 vhost_user_blk_server="auto"
-vhost_user_fs=""
+vhost_user_fs="$default_feature"
 kvm="auto"
 hax="auto"
 hvf="auto"
 whpx="auto"
-rdma=""
+rdma="$default_feature"
-pvrdma=""
+pvrdma="$default_feature"
 gprof="no"
 debug_tcg="no"
 debug="no"
 sanitizers="no"
 tsan="no"
-fortify_source=""
+fortify_source="$default_feature"
 strip_opt="yes"
 tcg_interpreter="no"
 bigendian="no"
 mingw32="no"
 gcov="no"
-EXESUF=""
+EXESUF="$default_feature"
 HOST_DSOSUF=".so"
 modules="no"
 module_upgrades="no"
@@ -370,81 +381,81 @@ pie=""
 qom_cast_debug="yes"
 trace_backends="log"
 trace_file="trace"
-spice=""
+spice="$default_feature"
-rbd=""
+rbd="$default_feature"
-smartcard=""
+smartcard="$default_feature"
 u2f="auto"
-libusb=""
+libusb="$default_feature"
-usb_redir=""
+usb_redir="$default_feature"
-opengl=""
+opengl="$default_feature"
 opengl_dmabuf="no"
 cpuid_h="no"
-avx2_opt=""
+avx2_opt="$default_feature"
 capstone="auto"
-lzo=""
+lzo="$default_feature"
-snappy=""
+snappy="$default_feature"
-bzip2=""
+bzip2="$default_feature"
-lzfse=""
+lzfse="$default_feature"
-zstd=""
+zstd="$default_feature"
-guest_agent=""
+guest_agent="$default_feature"
 guest_agent_with_vss="no"
 guest_agent_ntddscsi="no"
-guest_agent_msi=""
+guest_agent_msi="$default_feature"
-vss_win32_sdk=""
+vss_win32_sdk="$default_feature"
 win_sdk="no"
-want_tools=""
+want_tools="$default_feature"
-libiscsi=""
+libiscsi="$default_feature"
-libnfs=""
+libnfs="$default_feature"
 coroutine=""
-coroutine_pool=""
+coroutine_pool="$default_feature"
 debug_stack_usage="no"
 crypto_afalg="no"
-seccomp=""
+seccomp="$default_feature"
-glusterfs=""
+glusterfs="$default_feature"
 glusterfs_xlator_opt="no"
 glusterfs_discard="no"
 glusterfs_fallocate="no"
 glusterfs_zerofill="no"
 glusterfs_ftruncate_has_stat="no"
 glusterfs_iocb_has_stat="no"
-gtk=""
+gtk="$default_feature"
 gtk_gl="no"
 tls_priority="NORMAL"
-gnutls=""
+gnutls="$default_feature"
-nettle=""
+nettle="$default_feature"
 nettle_xts="no"
-gcrypt=""
+gcrypt="$default_feature"
 gcrypt_hmac="no"
 gcrypt_xts="no"
 qemu_private_xts="yes"
-auth_pam=""
+auth_pam="$default_feature"
-vte=""
+vte="$default_feature"
-virglrenderer=""
+virglrenderer="$default_feature"
-tpm=""
+tpm="$default_feature"
-libssh=""
+libssh="$default_feature"
-live_block_migration="yes"
+live_block_migration=${default_feature:-yes}
-numa=""
+numa="$default_feature"
 tcmalloc="no"
 jemalloc="no"
-replication="yes"
+replication=${default_feature:-yes}
-bochs="yes"
+bochs=${default_feature:-yes}
-cloop="yes"
+cloop=${default_feature:-yes}
-dmg="yes"
+dmg=${default_feature:-yes}
-qcow1="yes"
+qcow1=${default_feature:-yes}
-vdi="yes"
+vdi=${default_feature:-yes}
-vvfat="yes"
+vvfat=${default_feature:-yes}
-qed="yes"
+qed=${default_feature:-yes}
-parallels="yes"
+parallels=${default_feature:-yes}
 sheepdog="no"
-libxml2=""
+libxml2="$default_feature"
 debug_mutex="no"
-libpmem=""
+libpmem="$default_feature"
 default_devices="yes"
 plugins="no"
 fuzzing="no"
 rng_none="no"
-secret_keyring=""
+secret_keyring="$default_feature"
-libdaxctl=""
+libdaxctl="$default_feature"
 meson=""
 ninja=""
 skip_meson=no
@@ -455,7 +466,7 @@ fuse_lseek="auto"
 bogus_os="no"
 malloc_trim="auto"
 
-# parse CC options first
+# parse CC options second
 for opt do
   optarg=$(expr "x$opt" : 'x[^=]*=\(.*\)')
   case "$opt" in
@@ -798,7 +809,7 @@ Linux)
   audio_possible_drivers="oss alsa sdl pa"
   linux="yes"
   linux_user="yes"
-  vhost_user="yes"
+  vhost_user=${default_feature:-yes}
 ;;
 esac
 
@@ -942,6 +953,8 @@ for opt do
   ;;
   --without-default-devices) default_devices="no"
   ;;
+  --without-default-features) # processed above
+  ;;
   --enable-gprof) gprof="yes"
   ;;
   --enable-gcov) gcov="yes"
@@ -1747,7 +1760,8 @@ Advanced options (experts only):
   --gdb=GDB-path           gdb to use for gdbstub tests [$gdb_bin]
 
 Optional features, enabled with --enable-FEATURE and
-disabled with --disable-FEATURE, default is enabled if available:
+disabled with --disable-FEATURE, default is enabled if available
+(unless built with --without-default-features):
 
   system          all system emulation targets
   user            supported user emulation targets
@@ -6958,6 +6972,7 @@ NINJA=$ninja $meson setup \
         -Ddocs=$docs -Dsphinx_build=$sphinx_build -Dinstall_blobs=$blobs \
         -Dvhost_user_blk_server=$vhost_user_blk_server \
         -Dfuse=$fuse -Dfuse_lseek=$fuse_lseek \
+        $(if test "$default_features" = no; then echo "-Dauto_features=disabled"; fi) \
         $cross_arg \
         "$PWD" "$source_path"