Add subpath support to volumes in --mount option

All the backend work was done a while back for image volumes, so
this is effectively just plumbing the option in for volumes in
the parser logic. It's a little uglier than I'd like because
our volume mount parser produces an OCI Spec mount struct, which
doesn't have a field for subpath, so we have to pass through the
options array and parse it back out after, which is a little
gross. But not gross enough to rewrite that parsing logic.

Fixes #20661

Signed-off-by: Matt Heon <mheon@redhat.com>

Author: mheon

libpod/container.go

@@ -257,7 +257,7 @@ type ContainerNamedVolume struct {
 	// This is used for emptyDir volumes from a kube yaml
 	IsAnonymous bool `json:"setAnonymous,omitempty"`
 	// SubPath determines which part of the Source will be mounted in the container
-	SubPath string
+	SubPath string `json:",omitempty"`
 }
 
 // ContainerOverlayVolume is an overlay volume that will be mounted into the

pkg/specgenutil/volumes.go

@@ -377,6 +377,14 @@ func parseMountOptions(mountType string, args []string) (*spec.Mount, error) {
 				return nil, fmt.Errorf("host directory cannot be empty: %w", errOptionArg)
 			}
 			mnt.Source = value
+		case "subpath", "volume-subpath":
+			if mountType != define.TypeVolume {
+				return nil, fmt.Errorf("cannot set option %q on non-volume mounts", name)
+			}
+			if !hasValue {
+				return nil, fmt.Errorf("%v: %w", name, errOptionArg)
+			}
+			mnt.Options = append(mnt.Options, fmt.Sprintf("subpath=%s", value))
 		case "target", "dst", "destination":
 			if mnt.Destination != "" {
 				return nil, fmt.Errorf("cannot pass %q option more than once: %w", name, errOptionArg)
@@ -579,7 +587,21 @@ func getNamedVolume(args []string) (*specgen.NamedVolume, error) {
 	if len(mnt.Destination) == 0 {
 		return nil, errNoDest
 	}
-	newVolume.Options = mnt.Options
+
+	safeOpts := make([]string, 0, len(mnt.Options))
+	for _, opt := range mnt.Options {
+		splitOpt := strings.SplitN(opt, "=", 2)
+		if splitOpt[0] == "subpath" {
+			if len(splitOpt) != 2 {
+				return nil, fmt.Errorf("subpath was not provided a path")
+			}
+			newVolume.SubPath = splitOpt[1]
+		} else {
+			safeOpts = append(safeOpts, opt)
+		}
+	}
+
+	newVolume.Options = safeOpts
 	newVolume.Name = mnt.Source
 	newVolume.Dest = mnt.Destination
 	return newVolume, nil

test/e2e/run_volume_test.go

@@ -1069,4 +1069,24 @@ RUN chmod 755 /test1 /test2 /test3`, ALPINE)
 
 		mountVolumeAndCheckDirectory(volName, "/test3", "test2", imgName)
 	})
+
+	It("podman run --mount type=volume,subpath=", func() {
+		volName := "testvol"
+		mkvol := podmanTest.Podman([]string{"volume", "create", volName})
+		mkvol.WaitWithDefaultTimeout()
+		Expect(mkvol).Should(ExitCleanly())
+
+		subvol := "/test/test2/"
+		pathInCtr := "/mnt"
+		pathToCreate := filepath.Join(pathInCtr, subvol)
+		popvol := podmanTest.Podman([]string{"run", "-v", fmt.Sprintf("%s:/mnt", volName), ALPINE, "sh", "-c", fmt.Sprintf("mkdir -p %s; touch %s; touch %s", pathToCreate, filepath.Join(pathToCreate, "foo"), filepath.Join(pathToCreate, "bar"))})
+		popvol.WaitWithDefaultTimeout()
+		Expect(popvol).Should(ExitCleanly())
+
+		checkCtr := podmanTest.Podman([]string{"run", "--mount", fmt.Sprintf("type=volume,source=%s,target=%s,subpath=%s", volName, pathInCtr, subvol), ALPINE, "ls", pathInCtr})
+		checkCtr.WaitWithDefaultTimeout()
+		Expect(checkCtr).To(ExitCleanly())
+		Expect(checkCtr.OutputToString()).To(ContainSubstring("foo"))
+		Expect(checkCtr.OutputToString()).To(ContainSubstring("bar"))
+	})
 })