build, multiarch: support splitting build logs for --platform

Support splitting build logs for multi-arch builds ( `--platform` ) by
using `--logfile` and `--logsplit` which splits generated log file in the
convention `${file}_${platform_os}_${platform_arch}`.

Closes: https://github.com/containers/buildah/issues/3960

Signed-off-by: Aditya R <arajan@redhat.com>

cmd/buildah/build.go

@@ -253,6 +253,12 @@ func buildCmd(c *cobra.Command, inputArgs []string, iopts buildOptions) error {
 		reporter = f
 	}
 
+	if c.Flag("logsplit").Changed {
+		if !c.Flag("logfile").Changed {
+			return errors.Errorf("cannot use --logsplit without --logfile")
+		}
+	}
+
 	store, err := getStore(c)
 	if err != nil {
 		return err
@@ -383,6 +389,8 @@ func buildCmd(c *cobra.Command, inputArgs []string, iopts buildOptions) error {
 		IgnoreFile:              iopts.IgnoreFile,
 		Labels:                  iopts.Label,
 		Layers:                  layers,
+		LogFile:                 iopts.Logfile,
+		LogSplitByPlatform:      iopts.LogSplitByPlatform,
 		LogRusage:               iopts.LogRusage,
 		Manifest:                iopts.Manifest,
 		MaxPullPushRetries:      maxPullPushRetries,

define/build.go

@@ -151,6 +151,12 @@ type BuildOptions struct {
 	// Additional tags to add to the image that we write, if we know of a
 	// way to add them.
 	AdditionalTags []string
+	// Logfile specifies if log output is redirected to an external file
+	// instead of stdout, stderr.
+	LogFile string
+	// LogByPlatform tells imagebuildah to split log to different log files
+	// for each platform if logging to external file was selected.
+	LogSplitByPlatform bool
 	// Log is a callback that will print a progress message.  If no value
 	// is supplied, the message will be sent to Err (or os.Stderr, if Err
 	// is nil) by default.

docs/buildah-build.1.md

@@ -398,6 +398,11 @@ environment variable. `export BUILDAH_LAYERS=true`
 Log output which would be sent to standard output and standard error to the
 specified file instead of to standard output and standard error.
 
+**--logsplit** *bool-value*
+
+If --logfile and --platform is specified following flag allows end-users to split log file for each
+platform into different files with naming convention as `${logfile}_${platform-os}_${platform-arch}`.
+
 **--manifest** *listName*
 
 Name of the manifest list to which the built image will be added.  Creates the

imagebuildah/build.go

@@ -253,7 +253,25 @@ func BuildDockerfiles(ctx context.Context, store storage.Store, options define.B
 		}
 		platformOptions.Args = argsCopy
 		builds.Go(func() error {
-			thisID, thisRef, err := buildDockerfilesOnce(ctx, store, logger, logPrefix, platformOptions, paths, files)
+			loggerPerPlatform := logger
+			if platformOptions.LogFile != "" && platformOptions.LogSplitByPlatform {
+				logFile := platformOptions.LogFile + "_" + platformOptions.OS + "_" + platformOptions.Architecture
+				f, err := os.OpenFile(logFile, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600)
+				if err != nil {
+					return errors.Wrapf(err, "opening logfile: %q", logFile)
+				}
+				defer f.Close()
+				loggerPerPlatform = logrus.New()
+				loggerPerPlatform.SetOutput(f)
+				loggerPerPlatform.SetLevel(logrus.GetLevel())
+				stdout := f
+				stderr := f
+				reporter := f
+				platformOptions.Out = stdout
+				platformOptions.ReportWriter = reporter
+				platformOptions.Err = stderr
+			}
+			thisID, thisRef, err := buildDockerfilesOnce(ctx, store, loggerPerPlatform, logPrefix, platformOptions, paths, files)
 			if err != nil {
 				return err
 			}

pkg/cli/common.go

@@ -68,6 +68,7 @@ type BudResults struct {
 	Iidfile             string
 	Label               []string
 	Logfile             string
+	LogSplitByPlatform  bool
 	Manifest            string
 	NoHosts             bool
 	NoCache             bool
@@ -211,6 +212,7 @@ func GetBudFlags(flags *BudResults) pflag.FlagSet {
 	fs.IntVar(&flags.Jobs, "jobs", 1, "how many stages to run in parallel")
 	fs.StringArrayVar(&flags.Label, "label", []string{}, "set metadata for an image (default [])")
 	fs.StringVar(&flags.Logfile, "logfile", "", "log to `file` instead of stdout/stderr")
+	fs.BoolVar(&flags.LogSplitByPlatform, "logsplit", false, "split logfile to different files for each platform")
 	fs.Int("loglevel", 0, "NO LONGER USED, flag ignored, and hidden")
 	if err := fs.MarkHidden("loglevel"); err != nil {
 		panic(fmt.Sprintf("error marking the loglevel flag as hidden: %v", err))

tests/bud.bats

@@ -1704,6 +1704,25 @@ function _test_http() {
   test -s ${TEST_SCRATCH_DIR}/logfile
 }
 
+@test "bud-logfile-with-split-logfile-by-platform" {
+  mytmpdir=${TEST_SCRATCH_DIR}/my-dir
+  mkdir -p $mytmpdir
+
+  cat > $mytmpdir/Containerfile << _EOF
+FROM alpine
+COPY . .
+_EOF
+
+  rm -f ${TEST_SCRATCH_DIR}/logfile
+  run_buildah build --logfile ${TEST_SCRATCH_DIR}/logfile --logsplit --platform linux/arm64,linux/amd64 $WITH_POLICY_JSON ${mytmpdir}
+  run cat ${TEST_SCRATCH_DIR}/logfile_linux_arm64
+  expect_output --substring "FROM alpine"
+  expect_output --substring "[linux/arm64]"
+  run cat ${TEST_SCRATCH_DIR}/logfile_linux_amd64
+  expect_output --substring "FROM alpine"
+  expect_output --substring "[linux/amd64]"
+}
+
 @test "bud with ARGS" {
   _prefetch alpine
   target=alpine-image