buildkit: add from field to bind and cache mounts so images can be us…

…ed as source

Following commit adds buildkit like support for `from` field to `--mount=type=bind`
and `--mount=type=cache` so images and stage can be used as mount source.

Usage looks like
```dockerfile
RUN --mount=type=bind,source=.,from=<your-image>,target=/path ls /path
```
and
```dockerfile
RUN --mount=type=cache,from=<your-image>,target=/path ls /path
```

Signed-off-by: Aditya Rajan <[email protected]>

cmd/buildah/run.go

@@ -149,13 +149,20 @@ func runCmd(c *cobra.Command, args []string, iopts runInputOptions) error {
 		}
 	}
 
-	mounts, err := parse.GetVolumes(iopts.volumes, iopts.mounts, iopts.contextDir)
+	systemContext, err := parse.SystemContextFromOptions(c)
+	if err != nil {
+		return errors.Wrapf(err, "error building system context")
+	}
+	mounts, mountedImages, err := parse.GetVolumes(systemContext, store, iopts.volumes, iopts.mounts, iopts.contextDir)
 	if err != nil {
 		return err
 	}
 	options.Mounts = mounts
+	// Run() will automatically clean them up.
+	options.ExternalImageMounts = mountedImages
 
 	runerr := builder.Run(args, options)
+
 	if runerr != nil {
 		logrus.Debugf("error running %v in container %q: %v", args, builder.Container, runerr)
 	}

docs/Containerfile.5.md

@@ -114,7 +114,7 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
        Common Options:
 
-              · src, source: mount source spec for bind and volume. Mandatory for bind.
+              · src, source: mount source spec for bind and volume. Mandatory for bind. If `from` is specified, `src` is the subpath in the `from` field.
 
               · dst, destination, target: mount destination spec.
 
@@ -126,6 +126,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
               . bind-nonrecursive: do not setup a recursive bind mount.  By default it is recursive.
 
+              · from: stage or image name for the root of the source. Defaults to the build context.
+
        Options specific to tmpfs:
 
               · tmpfs-size: Size of the tmpfs mount in bytes. Unlimited by default in Linux.
@@ -146,6 +148,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
               · gid: gid for cache directory.
 
+              · from: stage name for the root of the source. Defaults to host cache directory.
+
 
 **RUN Secrets**
 

docs/buildah-run.1.md

@@ -122,7 +122,7 @@ Current supported mount TYPES are bind, cache, secret and tmpfs. <sup>[[1]](#Foo
 
        Common Options:
 
-              · src, source: mount source spec for bind and volume. Mandatory for bind.
+              · src, source: mount source spec for bind and volume. Mandatory for bind. If `from` is specified, `src` is the subpath in the `from` field.
 
               · dst, destination, target: mount destination spec.
 
@@ -134,6 +134,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs. <sup>[[1]](#Foo
 
               . bind-nonrecursive: do not setup a recursive bind mount.  By default it is recursive.
 
+              · from: stage or image name for the root of the source. Defaults to the build context.
+
        Options specific to tmpfs:
 
               · tmpfs-size: Size of the tmpfs mount in bytes. Unlimited by default in Linux.
@@ -158,6 +160,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs. <sup>[[1]](#Foo
 
               · gid: gid for cache directory.
 
+              · from: stage name for the root of the source. Defaults to host cache directory.
+
 **--network**, **--net**=*mode*
 
 Sets the configuration for the network namespace for the container.

imagebuildah/stage_executor.go

@@ -413,10 +413,56 @@ func (s *StageExecutor) Copy(excludes []string, copies ...imagebuilder.Copy) err
 	return nil
 }
 
+// Returns a map of StageName:StageMountpoint for RunOpts if any --mount with from is provided
+// check if RUN contains `--mount` with `from`. If yes pre-mount stages from executor for Run.
+// stages mounted here will we used be Run().
+func (s *StageExecutor) runStageMountPoints(mountList []string) (map[string]string, error) {
+	stageMountPoints := make(map[string]string)
+	for _, flag := range mountList {
+		if strings.Contains(flag, "from") {
+			arr := strings.SplitN(flag, ",", 2)
+			if len(arr) < 2 {
+				return nil, errors.Errorf("Invalid --mount command: %s", flag)
+			}
+			tokens := strings.Split(arr[1], ",")
+			for _, val := range tokens {
+				kv := strings.SplitN(val, "=", 2)
+				switch kv[0] {
+				case "from":
+					if kv[1] == "" {
+						return nil, errors.Errorf("unable to resolve argument for `from=`: from points to an empty value")
+					}
+					from, fromErr := imagebuilder.ProcessWord(kv[1], s.stage.Builder.Arguments())
+					if fromErr != nil {
+						return nil, errors.Wrapf(fromErr, "unable to resolve argument %q", kv[1])
+					}
+					// If the source's name corresponds to the
+					// result of an earlier stage, wait for that
+					// stage to finish being built.
+					if isStage, err := s.executor.waitForStage(s.ctx, from, s.stages[:s.index]); isStage && err != nil {
+						return nil, err
+					}
+					if otherStage, ok := s.executor.stages[from]; ok && otherStage.index < s.index {
+						stageMountPoints[from] = otherStage.mountPoint
+						break
+					}
+				default:
+					continue
+				}
+			}
+		}
+	}
+	return stageMountPoints, nil
+}
+
 // Run executes a RUN instruction using the stage's current working container
 // as a root directory.
 func (s *StageExecutor) Run(run imagebuilder.Run, config docker.Config) error {
 	logrus.Debugf("RUN %#v, %#v", run, config)
+	stageMountPoints, err := s.runStageMountPoints(run.Mounts)
+	if err != nil {
+		return err
+	}
 	if s.builder == nil {
 		return errors.Errorf("no build container available")
 	}
@@ -451,6 +497,8 @@ func (s *StageExecutor) Run(run imagebuilder.Run, config docker.Config) error {
 		Secrets:          s.executor.secrets,
 		SSHSources:       s.executor.sshsources,
 		RunMounts:        run.Mounts,
+		StageMountPoints: stageMountPoints,
+		SystemContext:    s.executor.systemContext,
 	}
 	if config.NetworkDisabled {
 		options.ConfigureNetwork = buildah.NetworkDisabled