[PATCH] tests/docker: Use --arch-only when building Debian cross images

[Philippe Mathieu-Daudé]

When building a Docker image based on debian10.docker on
a non-x86 host, we get:

 [2/4] RUN apt update &&     DEBIAN_FRONTEND=noninteractive eatmydata     apt 
build-dep -yy qemu
 Reading package lists... Done
 Building dependency tree
 Reading state information... Done
 Some packages could not be installed. This may mean that you have
 requested an impossible situation or if you are using the unstable
 distribution that some required packages have not yet been created
 or been moved out of Incoming.
 The following information may help to resolve the situation:

 The following packages have unmet dependencies:
  builddeps:qemu : Depends: gcc-s390x-linux-gnu but it is not installable
                   Depends: gcc-alpha-linux-gnu but it is not installable
 E: Unable to correct problems, you have held broken packages.

Fix by using the --arch-only option suggested here:
https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1866032/comments/1

Suggested-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 tests/docker/dockerfiles/debian-all-test-cross.docker | 2 +-
 tests/docker/dockerfiles/debian10.docker              | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/docker/dockerfiles/debian-all-test-cross.docker 
b/tests/docker/dockerfiles/debian-all-test-cross.docker
index dedcea58b46..593b7ef1023 100644
--- a/tests/docker/dockerfiles/debian-all-test-cross.docker
+++ b/tests/docker/dockerfiles/debian-all-test-cross.docker
@@ -11,7 +11,7 @@ FROM qemu/debian10
 # What we need to build QEMU itself
 RUN apt update && \
     DEBIAN_FRONTEND=noninteractive eatmydata \
-    apt build-dep -yy qemu
+    apt build-dep --arch-only -yy qemu
 
 # Add the foreign architecture we want and install dependencies
 RUN DEBIAN_FRONTEND=noninteractive eatmydata \
diff --git a/tests/docker/dockerfiles/debian10.docker 
b/tests/docker/dockerfiles/debian10.docker
index 9d42b5a4b81..d034acbd256 100644
--- a/tests/docker/dockerfiles/debian10.docker
+++ b/tests/docker/dockerfiles/debian10.docker
@@ -32,6 +32,6 @@ RUN apt update && \
         psmisc \
         python3 \
         python3-sphinx \
-        $(apt-get -s build-dep qemu | egrep ^Inst | fgrep '[all]' | cut -d\  
-f2)
+        $(apt-get -s build-dep --arch-only qemu | egrep ^Inst | fgrep '[all]' 
| cut -d\  -f2)
 
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