meson, cutils: allow non-relocatable installs

Say QEMU is configured with bindir = "/usr/bin" and a firmware path
that starts with "/usr/share/qemu".  Ever since QEMU 5.2, QEMU's
install has been relocatable: if you move qemu-system-x86_64 from
/usr/bin to /home/username/bin, it will start looking for firmware in
/home/username/share/qemu.  Previously, you would get a non-relocatable
install where the moved QEMU will keep looking for firmware in
/usr/share/qemu.

Windows almost always wants relocatable installs, and in fact that
is why QEMU 5.2 introduced relocatability in the first place.
However, newfangled distribution mechanisms such as AppImage
(https://docs.appimage.org/reference/best-practices.html), and
possibly NixOS, also dislike using at runtime the absolute paths
that were established at build time.

On POSIX systems you almost never care; if you do, your usecase
dictates which one is desirable, so there's no single answer.
Obviously relocatability works fine most of the time, because not many
people have complained about QEMU's switch to relocatable install,
and that's why until now there was no way to disable relocatability.

But a non-relocatable, non-modular binary can help if you want to do
experiments with old firmware and new QEMU or vice versa (because you
can just upgrade/downgrade the firmware package, and use rpm2cpio or
similar to extract the QEMU binaries outside /usr), so allow both.
This patch allows one to build a non-relocatable install using a new
option to configure.  Why?  Because it's not too hard, and because
it helps the user double check the relocatability of their install.

Note that the same code that handles relocation also lets you run QEMU
from the build tree and pick e.g. firmware files from the source tree
transparently.  Therefore that part remains active with this patch,
even if you configure with --disable-relocatable.

Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/meson.build b/meson.build
index 010d2c649c2366dff8e6936f547286f35f50d90d..1be9f92f7da8df19da9159464c8bf05f19e6012b 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -2111,6 +2111,7 @@ config_host_data.set('CONFIG_OPENGL', opengl.found())
 config_host_data.set('CONFIG_PLUGIN', get_option('plugins'))
 config_host_data.set('CONFIG_RBD', rbd.found())
 config_host_data.set('CONFIG_RDMA', rdma.found())
+config_host_data.set('CONFIG_RELOCATABLE', get_option('relocatable'))
 config_host_data.set('CONFIG_SAFESTACK', get_option('safe_stack'))
 config_host_data.set('CONFIG_SDL', sdl.found())
 config_host_data.set('CONFIG_SDL_IMAGE', sdl_image.found())
@@ -4054,6 +4055,7 @@ if 'simple' in get_option('trace_backends')
 endif
 summary_info += {'D-Bus display':     dbus_display}
 summary_info += {'QOM debugging':     get_option('qom_cast_debug')}
+summary_info += {'Relocatable install': get_option('relocatable')}
 summary_info += {'vhost-kernel support': have_vhost_kernel}
 summary_info += {'vhost-net support': have_vhost_net}
 summary_info += {'vhost-user support': have_vhost_user}
@@ -4356,3 +4358,21 @@ if host_arch == 'unknown' or not supported_oses.contains(targetos)
   message('If you want to help supporting QEMU on this platform, please')
   message('contact the developers at qemu-devel@nongnu.org.')
 endif
+
+actually_reloc = get_option('relocatable')
+# check if get_relocated_path() is actually able to relocate paths
+if get_option('relocatable') and \
+  not (get_option('prefix') / get_option('bindir')).startswith(get_option('prefix') / '')
+  message()
+  warning('bindir not included within prefix, the installation will not be relocatable.')
+  actually_reloc = false
+endif
+if not actually_reloc and (targetos == 'windows' or get_option('relocatable'))
+  if targetos == 'windows'
+    message()
+    warning('Windows installs should usually be relocatable.')
+  endif
+  message()
+  message('QEMU will have to be installed under ' + get_option('prefix') + '.')
+  message('Use --disable-relocatable to remove this warning.')
+endif

diff --git a/meson_options.txt b/meson_options.txt
index 6a17b9096809512d4d55acfd66f993aeacda31d4..e237b268469076491b218dfe76471655376520ba 100644 (file)
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -101,6 +101,8 @@ 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('relocatable', type : 'boolean', value : 'true',
+       description: 'toggle relocatable install')
 option('vfio_user_server', type: 'feature', value: 'disabled',
        description: 'vfio-user server support')
 option('dbus_display', type: 'feature', value: 'auto',

diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
index 2a74b0275b36a122504bf9268f0da94da22e2040..d4b89e6b4435009892ded1757583138521c142c4 100644 (file)
--- a/scripts/meson-buildoptions.sh
+++ b/scripts/meson-buildoptions.sh
@@ -17,6 +17,7 @@ meson_options_help() {
   printf "%s\n" '                           code for the Hexagon frontend'
   printf "%s\n" '  --disable-install-blobs  install provided firmware blobs'
   printf "%s\n" '  --disable-qom-cast-debug cast debugging support'
+  printf "%s\n" '  --disable-relocatable    toggle relocatable install'
   printf "%s\n" '  --docdir=VALUE           Base directory for documentation installation'
   printf "%s\n" '                           (can be empty) [share/doc]'
   printf "%s\n" '  --enable-block-drv-whitelist-in-tools'
@@ -421,6 +422,8 @@ _meson_option_parse() {
     --disable-rbd) printf "%s" -Drbd=disabled ;;
     --enable-rdma) printf "%s" -Drdma=enabled ;;
     --disable-rdma) printf "%s" -Drdma=disabled ;;
+    --enable-relocatable) printf "%s" -Drelocatable=true ;;
+    --disable-relocatable) printf "%s" -Drelocatable=false ;;
     --enable-replication) printf "%s" -Dreplication=enabled ;;
     --disable-replication) printf "%s" -Dreplication=disabled ;;
     --enable-rng-none) printf "%s" -Drng_none=true ;;

diff --git a/util/cutils.c b/util/cutils.c
index c99d26c5e2d2e45de1a19a9cc37207d2312e1690..64f817b477bbfa2f04a33b0948b6be7fa1a3a63d 100644 (file)
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -1178,9 +1178,11 @@ char *get_relocated_path(const char *dir)
 #else
         g_string_append(result, dir);
 #endif
-    } else if (!starts_with_prefix(dir) || !starts_with_prefix(bindir)) {
-        g_string_assign(result, dir);
-    } else {
+        goto out;
+    }
+
+    if (IS_ENABLED(CONFIG_RELOCATABLE) &&
+        starts_with_prefix(dir) && starts_with_prefix(bindir)) {
         g_string_assign(result, exec_dir);
 
         /* Advance over common components.  */
@@ -1203,7 +1205,10 @@ char *get_relocated_path(const char *dir)
             assert(G_IS_DIR_SEPARATOR(dir[-1]));
             g_string_append(result, dir - 1);
         }
+        goto out;
     }
 
+    g_string_assign(result, dir);
+out:
     return g_string_free(result, false);
 }