test/imgtestlib: capture the build log output

Now that we're building all images on the same runner, the log becomes
too long and noisy and hits the limits of the CI log length.
Capture build log output and errors and store them in a path that will
be used as a CI artifact we can review.

Note that runcmd() will print stdout and stderr when a command fails.

Author: achilleas-k

test/scripts/imgtestlib/build.py

@@ -3,9 +3,11 @@
 from typing import Dict
 
 from .gitlab import log_section
-from .run import runcmd, runcmd_nc
+from .run import runcmd
 from .testenv import get_host_distro, get_osbuild_commit, rng_seed_env
 
+BUILD_LOG_PATH = "/build/logs"
+
 
 @log_section("Building image")
 def build_image(distro, arch, image_type, config_path):
@@ -21,7 +23,10 @@ def build_image(distro, arch, image_type, config_path):
 
     cmd = ["sudo", "-E", "./bin/build", "--output", "./build", "--checkpoints", "build",
            "--distro", distro, "--arch", arch, "--type", image_type, "--config", config_path]
-    runcmd_nc(cmd, extra_env=rng_seed_env())
+    stdout, stderr = runcmd(cmd, extra_env=rng_seed_env())
+
+    build_name = gen_build_name(distro, arch, image_type, config_name)
+    save_logs(build_name, stdout, stderr)
 
     # Build artifacts are owned by root. Make them world accessible.
     runcmd(["sudo", "chmod", "a+rwX", "-R", "./build"])
@@ -85,3 +90,14 @@ def gen_build_name(distro, arch, image_type, config_name):
 
 def _u(s):
     return s.replace("-", "_")
+
+
+def save_logs(build_name, out, err):
+    """
+    Save stdout and stderr output for a job to the BUILD_LOG_PATH.
+    """
+    os.makedirs(BUILD_LOG_PATH, exist_ok=True)
+    with open(os.path.join(BUILD_LOG_PATH, f"{build_name}.out"), mode="w", encoding="utf-8") as log:
+        log.write(out)
+    with open(os.path.join(BUILD_LOG_PATH, f"{build_name}.err"), mode="w", encoding="utf-8") as log:
+        log.write(err)