diffapply: make overwritten dirs opaque.

A previous commit fixed an issue where directories that overwrite
whiteout devices needed to be set to be opaque. While that was needed,
it wasn't enough because directories also need to be set opaque if they
are overwriting anything that isn't a directory, such as a file or a
symlink. This commit updates the code to handle that situation in
general.

Signed-off-by: Erik Sipsma <[email protected]>

client/mergediff_test.go

@@ -1077,7 +1077,7 @@ func diffOpTestCases() (tests []integration.Test) {
 		}
 		return []integration.Test{
 			verifyContents{
-				// Verifies that when a directory with contents is used a a base layer
+				// Verifies that when a directory with contents is used as a base layer
 				// in a merge, subsequent merges that first delete the dir (resulting in
 				// a whiteout device w/ overlay snapshotters) and then recreate the dir
 				// correctly set it as opaque.
@@ -1092,6 +1092,19 @@ func diffOpTestCases() (tests []integration.Test) {
 					fstest.CreateFile("/dir/b", nil, 0644),
 				),
 			},
+			verifyContents{
+				// Same as above, but with a file overwrite instead of an rm
+				name: "TestDiffMergeOpaqueRegressionWithFileOverwrite",
+				state: llb.Merge([]llb.State{
+					base().File(llb.Mkfile("/dir/a", 0644, nil)),
+					llb.Scratch().File(llb.Mkfile("/dir", 0644, nil)),
+					base().File(llb.Mkfile("/dir/b", 0644, nil)),
+				}),
+				contents: apply(
+					fstest.CreateDir("/dir", 0755),
+					fstest.CreateFile("/dir/b", nil, 0644),
+				),
+			},
 		}
 	}()...)
 

snapshot/diffapply_unix.go

@@ -266,17 +266,18 @@ func (a *applier) applyDelete(ctx context.Context, ca *changeApply) (bool, error
 		return false, nil
 	}
 
-	if overwrite && a.createWhiteoutDelete && isWhiteoutDevice(ca.dstStat) && ca.srcStat.Mode&unix.S_IFMT == unix.S_IFDIR {
-		// If we are overwriting a whiteout device with a directory, we need this new dir to be opaque
-		// so that any files from lowerdirs under it are not visible.
-		ca.setOpaque = true
-	}
-
 	if err := os.RemoveAll(ca.dstPath); err != nil {
 		return false, errors.Wrap(err, "failed to remove during apply")
 	}
 	ca.dstStat = nil
 
+	if overwrite && a.createWhiteoutDelete && ca.srcStat.Mode&unix.S_IFMT == unix.S_IFDIR {
+		// If we are using an overlay snapshotter and overwriting an existing non-directory
+		// with a directory, we need this new dir to be opaque so that any files from lowerdirs
+		// under it are not visible.
+		ca.setOpaque = true
+	}
+
 	if deleteOnly && a.createWhiteoutDelete {
 		// only create a whiteout device if there is something to delete
 		var foundLower bool
@@ -849,8 +850,3 @@ func needsUserXAttr(ctx context.Context, sn Snapshotter, lm leases.Manager) (boo
 	}
 	return userxattr, nil
 }
-
-func isWhiteoutDevice(st *syscall.Stat_t) bool {
-	// it's a whiteout if it's a char device and has a major/minor of 0/0
-	return st != nil && st.Mode&unix.S_IFMT == unix.S_IFCHR && st.Rdev == unix.Mkdev(0, 0)
-}