I interpreted CONFIG_VHOST_USER as controlling only QEMU's vhost-user
device frontends. However, virtiofsd and contrib/ vhost-user device
backends are also controlled by CONFIG_VHOST_USER. Make the
vhost-user-blk server depend on CONFIG_VHOST_USER for consistency.

Now the following error is printed when the vhost-user-blk server is
enabled without CONFIG_VHOST_USER:

  $ ./configure --disable-vhost-user --enable-vhost-user-blk ...
  ../meson.build:761:8: ERROR: Problem encountered: vhost_user_blk_server requires vhost-user support

Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Suggested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 meson.build | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 4f5c916557..ee3719da39 100644
--- a/meson.build
+++ b/meson.build
@@ -751,11 +751,14 @@ statx_test = '''
 
 has_statx = cc.links(statx_test)
 
-have_vhost_user_blk_server = (targetos == 'linux')
+have_vhost_user_blk_server = (targetos == 'linux' and
+    'CONFIG_VHOST_USER' in config_host)
 
 if get_option('vhost_user_blk_server').enabled()
     if targetos != 'linux'
         error('vhost_user_blk_server requires linux')
+    elif 'CONFIG_VHOST_USER' not in config_host
+        error('vhost_user_blk_server requires vhost-user support')
     endif
 elif get_option('vhost_user_blk_server').disabled() or not have_system
     have_vhost_user_blk_server = false
-- 
2.28.0

On 11/10/20 6:11 PM, Stefan Hajnoczi wrote:
> I interpreted CONFIG_VHOST_USER as controlling only QEMU's vhost-user
> device frontends. However, virtiofsd and contrib/ vhost-user device
> backends are also controlled by CONFIG_VHOST_USER. Make the
> vhost-user-blk server depend on CONFIG_VHOST_USER for consistency.

Possible follow up cleanup is to rename variable including
"frontend/backend".

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> 
> Now the following error is printed when the vhost-user-blk server is
> enabled without CONFIG_VHOST_USER:
> 
>   $ ./configure --disable-vhost-user --enable-vhost-user-blk ...
>   ../meson.build:761:8: ERROR: Problem encountered: vhost_user_blk_server requires vhost-user support
> 
> Suggested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Suggested-by: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  meson.build | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

On Wed, Nov 11, 2020 at 10:25:22AM +0100, Philippe Mathieu-Daudé wrote:
> On 11/10/20 6:11 PM, Stefan Hajnoczi wrote:
> > I interpreted CONFIG_VHOST_USER as controlling only QEMU's vhost-user
> > device frontends. However, virtiofsd and contrib/ vhost-user device
> > backends are also controlled by CONFIG_VHOST_USER. Make the
> > vhost-user-blk server depend on CONFIG_VHOST_USER for consistency.
> 
> Possible follow up cleanup is to rename variable including
> "frontend/backend".

Yes, vhost-user-blk-server and related names don't follow vhost-user
terminology.

Stefan