Fix an issue where copyup could fail with ENOENT

This one is rather bizarre because it triggers only on some
systems. I've included a CI test, for example, but I'm 99% sure
we use images in CI that have volumes over empty directories, and
the earlier patch to change copy-up implementation passed CI
without complaint.

I can reproduce this on a stock F33 VM, but that's the only place
I have been able to see it.

Regardless, the issue: under certain as-yet-unidentified
environmental conditions, the copier.Get method will return an
ENOENT attempting to stream a directory that is empty. Work
around this by avoiding the copy altogether in this case.

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

libpod/container_internal.go

@@ -1617,6 +1617,17 @@ func (c *Container) mountNamedVolume(v *ContainerNamedVolume, mountpoint string)
 		if !srcStat.IsDir() {
 			return vol, nil
 		}
+		// Read contents, do not bother continuing if it's empty. Fixes
+		// a bizarre issue where something copier.Get will ENOENT on
+		// empty directories and sometimes it will not.
+		// RHBZ#1928643
+		srcContents, err := ioutil.ReadDir(srcDir)
+		if err != nil {
+			return nil, errors.Wrapf(err, "error reading contents of source directory for copy up into volume %s", vol.Name())
+		}
+		if len(srcContents) == 0 {
+			return vol, nil
+		}
 
 		// Buildah Copier accepts a reader, so we'll need a pipe.
 		reader, writer := io.Pipe()

test/e2e/run_volume_test.go

@@ -322,6 +322,18 @@ RUN sh -c "cd /etc/apk && ln -s ../../testfile"`
 		Expect(outputSession.OutputToString()).To(Equal(baselineOutput))
 	})
 
+	It("podman named volume copyup empty directory", func() {
+		baselineSession := podmanTest.Podman([]string{"run", "--rm", "-t", "-i", ALPINE, "ls", "/srv"})
+		baselineSession.WaitWithDefaultTimeout()
+		Expect(baselineSession.ExitCode()).To(Equal(0))
+		baselineOutput := baselineSession.OutputToString()
+
+		outputSession := podmanTest.Podman([]string{"run", "-t", "-i", "-v", "/srv", ALPINE, "ls", "/srv"})
+		outputSession.WaitWithDefaultTimeout()
+		Expect(outputSession.ExitCode()).To(Equal(0))
+		Expect(outputSession.OutputToString()).To(Equal(baselineOutput))
+	})
+
 	It("podman read-only tmpfs conflict with volume", func() {
 		session := podmanTest.Podman([]string{"run", "--rm", "-t", "-i", "--read-only", "-v", "tmp_volume:" + dest, ALPINE, "touch", dest + "/a"})
 		session.WaitWithDefaultTimeout()