buildah: add prune command and expose CleanCacheMount API

* Just like buildkit buildah must allow cleaning the buildcache and cache
generated on host by `--mount=type=cache` just like buildkit's `prune`
command.

* Also expose `CleanCacheMount` API so other tools like `podman` can use
  it.

See: https://github.com/moby/buildkit#cache
Closes: https://github.com/containers/buildah/issues/4486

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

cmd/buildah/prune.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"context"
+	"fmt"
+
+	internalParse "github.com/containers/buildah/internal/parse"
+	buildahcli "github.com/containers/buildah/pkg/cli"
+	"github.com/containers/buildah/pkg/parse"
+	"github.com/containers/common/libimage"
+	"github.com/hashicorp/go-multierror"
+	"github.com/spf13/cobra"
+)
+
+type pruneOptions struct {
+	force bool
+	all   bool
+}
+
+func init() {
+	var (
+		pruneDescription = `
+Cleanup intermediate images as well as build and mount cache.`
+		opts pruneOptions
+	)
+	pruneCommand := &cobra.Command{
+		Use:   "prune",
+		Short: "Cleanup intermediate images as well as build and mount cache",
+		Long:  pruneDescription,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return pruneCmd(cmd, args, opts)
+		},
+		Example: `buildah prune
+  buildah prune`,
+	}
+	pruneCommand.SetUsageTemplate(UsageTemplate())
+
+	flags := pruneCommand.Flags()
+	flags.SetInterspersed(false)
+
+	flags.BoolVarP(&opts.all, "all", "a", false, "remove all unused images")
+	flags.BoolVarP(&opts.force, "force", "f", false, "force removal of the image and any containers using the image")
+
+	rootCmd.AddCommand(pruneCommand)
+}
+
+func pruneCmd(c *cobra.Command, args []string, iopts pruneOptions) error {
+	if err := buildahcli.VerifyFlagsArgsOrder(args); err != nil {
+		return err
+	}
+
+	store, err := getStore(c)
+	if err != nil {
+		return err
+	}
+
+	systemContext, err := parse.SystemContextFromOptions(c)
+	if err != nil {
+		return err
+	}
+	runtime, err := libimage.RuntimeFromStore(store, &libimage.RuntimeOptions{SystemContext: systemContext})
+	if err != nil {
+		return err
+	}
+
+	err = internalParse.CleanCacheMount()
+	if err != nil {
+		return err
+	}
+
+	options := &libimage.RemoveImagesOptions{
+		Filters: []string{"readonly=false"},
+	}
+	if !iopts.all {
+		options.Filters = append(options.Filters, "dangling=true")
+		options.Filters = append(options.Filters, "intermediate=true")
+	}
+	options.Force = iopts.force
+
+	rmiReports, rmiErrors := runtime.RemoveImages(context.Background(), args, options)
+	for _, r := range rmiReports {
+		for _, u := range r.Untagged {
+			fmt.Printf("untagged: %s\n", u)
+		}
+	}
+	for _, r := range rmiReports {
+		if r.Removed {
+			fmt.Printf("%s\n", r.ID)
+		}
+	}
+
+	var multiE *multierror.Error
+	multiE = multierror.Append(multiE, rmiErrors...)
+	return multiE.ErrorOrNil()
+}

docs/buildah-prune.1.md

@@ -0,0 +1,33 @@
+# buildah-rmi "1" "Jan 2023" "buildah"
+
+## NAME
+
+buildah\-prune - Cleanup intermediate images as well as build and mount cache.
+
+## SYNOPSIS
+
+**buildah prune**
+
+## DESCRIPTION
+
+Cleanup intermediate images as well as build and mount cache.
+
+## OPTIONS
+
+**--all**, **-a**
+
+All local images will be removed from the system that do not have containers using the image as a reference image.
+
+**--force**, **-f**
+
+This option will cause Buildah to remove all containers that are using the image before removing the image from the system.
+
+## EXAMPLE
+
+buildah prune
+
+buildah prune --force
+
+## SEE ALSO
+
+buildah(1), containers-registries.conf(5), containers-storage.conf(5)

docs/buildah.1.md

@@ -159,6 +159,7 @@ Buildah can set up environment variables from the env entry in the [engine] tabl
 | logout     | [buildah-logout(1)](buildah-logout.1.md)         | Logout of a container registry                                                                       |
 | manifest   | [buildah-manifest(1)](buildah-manifest.1.md)     | Create and manipulate manifest lists and image indexes.                                              |
 | mount      | [buildah-mount(1)](buildah-mount.1.md)           | Mount the working container's root filesystem.                                                       |
+| prune      | [buildah-prune(1)](buildah-prune.1.md)           | Cleanup intermediate images as well as build and mount cache.                                        |
 | pull       | [buildah-pull(1)](buildah-pull.1.md)             | Pull an image from the specified location.                                                           |
 | push       | [buildah-push(1)](buildah-push.1.md)             | Push an image from local storage to elsewhere.                                                       |
 | rename     | [buildah-rename(1)](buildah-rename.1.md)         | Rename a local container.                                                                            |

internal/parse/parse.go

@@ -191,6 +191,12 @@ func GetBindMount(ctx *types.SystemContext, args []string, contextDir string, st
 	return newMount, fromImage, nil
 }
 
+// CleanCacheMount gets the cache parent created by `--mount=type=cache` and removes it.
+func CleanCacheMount() error {
+	cacheParent := filepath.Join(internalUtil.GetTempDir(), BuildahCacheDir+"-"+strconv.Itoa(unshare.GetRootlessUID()))
+	return os.RemoveAll(cacheParent)
+}
+
 // GetCacheMount parses a single cache mount entry from the --mount flag.
 //
 // If this function succeeds and returns a non-nil *lockfile.LockFile, the caller must unlock it (when??).

tests/bud.bats

@@ -5549,6 +5549,21 @@ _EOF
   run_buildah rmi -f testbud2
 }
 
+@test "bud-with-mount-cache-like-buildkit with buildah prune should clear the cache" {
+  skip_if_no_runtime
+  skip_if_in_container
+  local contextdir=${TEST_SCRATCH_DIR}/buildkit-mount
+  cp -R $BUDFILES/buildkit-mount $contextdir
+  # try writing something to persistent cache
+  run_buildah build -t testbud $WITH_POLICY_JSON -f $contextdir/Dockerfilecachewrite
+  # prune the mount cache
+  run_buildah prune
+  # try reading something from persistent cache in a different build
+  run_buildah 1 build -t testbud2 $WITH_POLICY_JSON -f $contextdir/Dockerfilecacheread
+  expect_output --substring "No such file or directory"
+  run_buildah rmi -f testbud
+}
+
 @test "bud-with-mount-cache-like-buildkit-verify-default-selinux-option" {
   skip_if_no_runtime
   skip_if_in_container