The vhost-user protocol uses the Linux eventfd feature and is typically
connected to Linux kvm.ko ioeventfd and irqfd file descriptors. The
protocol specification in docs/interop/vhost-user.rst does not describe
how platforms without eventfd support work.

The QEMU vhost-user devices compile on other POSIX host operating
systems because eventfd usage is abstracted in QEMU. The libvhost-user
programs in contrib/ do not compile but we failed to notice since they
are not built by default.

Make it clear that vhost-user is only supported on Linux for the time
being. If someone wishes to support it on other platforms then the
details can be added to vhost-user.rst and CI jobs can test the feature
to prevent bitrot.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 configure | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/configure b/configure
index 5ae73fa32c..ef431f86c0 100755
--- a/configure
+++ b/configure
@@ -328,7 +328,7 @@ vhost_net=""
 vhost_crypto=""
 vhost_scsi=""
 vhost_vsock=""
-vhost_user=""
+vhost_user="no"
 vhost_user_blk_server="auto"
 vhost_user_fs=""
 kvm="auto"
@@ -718,7 +718,6 @@ fi
 case $targetos in
 MINGW32*)
   mingw32="yes"
-  vhost_user="no"
   audio_possible_drivers="dsound sdl"
   if check_include dsound.h; then
     audio_drv_list="dsound"
@@ -797,6 +796,7 @@ Linux)
   audio_possible_drivers="oss alsa sdl pa"
   linux="yes"
   linux_user="yes"
+  vhost_user="yes"
 ;;
 esac
 
@@ -2339,9 +2339,8 @@ fi
 # vhost interdependencies and host support
 
 # vhost backends
-test "$vhost_user" = "" && vhost_user=yes
-if test "$vhost_user" = "yes" && test "$mingw32" = "yes"; then
-  error_exit "vhost-user isn't available on win32"
+if test "$vhost_user" = "yes" && test "$linux" != "yes"; then
+  error_exit "vhost-user is only available on Linux"
 fi
 test "$vhost_vdpa" = "" && vhost_vdpa=$linux
 if test "$vhost_vdpa" = "yes" && test "$linux" != "yes"; then
-- 
2.28.0

On 10/11/2020 18.11, Stefan Hajnoczi wrote:
> The vhost-user protocol uses the Linux eventfd feature and is typically
> connected to Linux kvm.ko ioeventfd and irqfd file descriptors. The
> protocol specification in docs/interop/vhost-user.rst does not describe
> how platforms without eventfd support work.
> 
> The QEMU vhost-user devices compile on other POSIX host operating
> systems because eventfd usage is abstracted in QEMU. The libvhost-user
> programs in contrib/ do not compile but we failed to notice since they
> are not built by default.
> 
> Make it clear that vhost-user is only supported on Linux for the time
> being. If someone wishes to support it on other platforms then the
> details can be added to vhost-user.rst and CI jobs can test the feature
> to prevent bitrot.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  configure | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/configure b/configure
> index 5ae73fa32c..ef431f86c0 100755
> --- a/configure
> +++ b/configure
> @@ -328,7 +328,7 @@ vhost_net=""
>  vhost_crypto=""
>  vhost_scsi=""
>  vhost_vsock=""
> -vhost_user=""
> +vhost_user="no"
>  vhost_user_blk_server="auto"
>  vhost_user_fs=""
>  kvm="auto"
> @@ -718,7 +718,6 @@ fi
>  case $targetos in
>  MINGW32*)
>    mingw32="yes"
> -  vhost_user="no"
>    audio_possible_drivers="dsound sdl"
>    if check_include dsound.h; then
>      audio_drv_list="dsound"
> @@ -797,6 +796,7 @@ Linux)
>    audio_possible_drivers="oss alsa sdl pa"
>    linux="yes"
>    linux_user="yes"
> +  vhost_user="yes"
>  ;;
>  esac
>  
> @@ -2339,9 +2339,8 @@ fi
>  # vhost interdependencies and host support
>  
>  # vhost backends
> -test "$vhost_user" = "" && vhost_user=yes
> -if test "$vhost_user" = "yes" && test "$mingw32" = "yes"; then
> -  error_exit "vhost-user isn't available on win32"
> +if test "$vhost_user" = "yes" && test "$linux" != "yes"; then
> +  error_exit "vhost-user is only available on Linux"
>  fi
>  test "$vhost_vdpa" = "" && vhost_vdpa=$linux
>  if test "$vhost_vdpa" = "yes" && test "$linux" != "yes"; then
> 

Reviewed-by: Thomas Huth <thuth@redhat.com>

On 11/10/20 6:11 PM, Stefan Hajnoczi wrote:
> The vhost-user protocol uses the Linux eventfd feature and is typically
> connected to Linux kvm.ko ioeventfd and irqfd file descriptors. The
> protocol specification in docs/interop/vhost-user.rst does not describe
> how platforms without eventfd support work.
> 
> The QEMU vhost-user devices compile on other POSIX host operating
> systems because eventfd usage is abstracted in QEMU. The libvhost-user
> programs in contrib/ do not compile but we failed to notice since they
> are not built by default.
> 
> Make it clear that vhost-user is only supported on Linux for the time
> being. If someone wishes to support it on other platforms then the
> details can be added to vhost-user.rst and CI jobs can test the feature
> to prevent bitrot.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  configure | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

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