pkg/subsystem/linux: determine parent-child relations

For that, extract a coincidence count matrix from a path coverage, then
apply the following rule.

Subsystem A is a child of B if both hold true:
1) More than 2/3 of paths that relate to A also relate to B.
2) B covers more directory tree entities than A.

1 files changed, 44 insertions, 10 deletions

diff --git a/pkg/subsystem/linux/subsystems_test.go b/pkg/subsystem/linux/subsystems_test.go
index 09d835e3f..52cf8540c 100644
--- a/pkg/subsystem/linux/subsystems_test.go
+++ b/pkg/subsystem/linux/subsystems_test.go
@@ -20,9 +20,11 @@ func TestGroupLinuxSubsystems(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	// The regexps used for matching rules may change later, so let's not compare them here.
 	for _, s := range subsystems {
+		// The regexps used for matching rules may change later, so let's not compare them here.
 		s.PathRules = nil
+		// It complicates the test, so let's skip it here.
+		s.Parents = nil
 	}
 	expected := []*entity.Subsystem{
 		{
@@ -36,8 +38,14 @@ func TestGroupLinuxSubsystems(t *testing.T) {
 			Maintainers: []string{"email_ext4@email.com", "email_ext4_2@email.com"},
 		},
 		{
-			Name:  "mm",
-			Lists: []string{"linux-mm@kvack.org"},
+			Name:        "mm",
+			Lists:       []string{"linux-mm@kvack.org"},
+			Maintainers: []string{"email_mm@email.com"},
+		},
+		{
+			Name:        "tmpfs",
+			Lists:       []string{"tmpfs@kvack.org"},
+			Maintainers: []string{"email_shmem@email.com"},
 		},
 		{
 			Name:        "kernel",
@@ -57,7 +65,8 @@ func TestCustomCallRules(t *testing.T) {
 		t.Fatal(err)
 	}
 	expectCalls := map[string][]string{
-		"ext4": []string{"syz_mount_image$ext4"},
+		"ext4":  {"syz_mount_image$ext4"},
+		"tmpfs": {"syz_mount_image$tmpfs"},
 	}
 	gotCalls := map[string][]string{}
 	for _, s := range subsystems {
@@ -106,9 +115,8 @@ func TestLinuxSubsystemPaths(t *testing.T) {
 			list: []string{"kernel", "mm"},
 		},
 		{
-			// Shmem has no mailing list.
 			path: `mm/shmem.c`,
-			list: []string{"kernel", "mm"},
+			list: []string{"kernel", "mm", "tmpfs"},
 		},
 		{
 			path: `include/net/ah.h`,
@@ -133,6 +141,32 @@ func TestLinuxSubsystemPaths(t *testing.T) {
 	}
 }
 
+func TestLinuxSubsystemParents(t *testing.T) {
+	// For the list of subsystems, see TestLinuxSubsystemsList.
+	// Here we rely on the same ones.
+	repo := prepareTestLinuxRepo(t, []byte(testMaintainers))
+	subsystems, err := listFromRepoInner(repo, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expectParents := map[string][]string{
+		"ext4":     {"fs"},
+		"mm":       {"kernel"},
+		"fs":       {"kernel"},
+		"tmpfs":    {"mm"},
+		"freevxfs": {"fs"},
+	}
+	for _, s := range subsystems {
+		names := []string{}
+		for _, p := range s.Parents {
+			names = append(names, p.Name)
+		}
+		assert.ElementsMatch(t, names, expectParents[s.Name],
+			"wrong parents for %#v", s.Name)
+	}
+}
+
 func prepareTestLinuxRepo(t *testing.T, maintainers []byte) fs.FS {
 	return fstest.MapFS{
 		`fs/ext4/fsync.c`:        {},
@@ -152,9 +186,9 @@ func prepareTestLinuxRepo(t *testing.T, maintainers []byte) fs.FS {
 var (
 	testRules = &customRules{
 		subsystemCalls: map[string][]string{
-			"ext4":  []string{"syz_mount_image$ext4"},
-			"vxfs":  []string{"syz_mount_image$vxfs"},
-			"tmpfs": []string{"syz_mount_image$tmpfs"},
+			"ext4":  {"syz_mount_image$ext4"},
+			"vxfs":  {"syz_mount_image$vxfs"},
+			"tmpfs": {"syz_mount_image$tmpfs"},
 		},
 	}
 	testMaintainers = `
@@ -212,7 +246,7 @@ F:	tools/testing/selftests/vm/
 
 TMPFS (SHMEM FILESYSTEM)
 M:	Developer <email_shmem@email.com>
-L:	linux-mm@kvack.org
+L:	tmpfs@kvack.org
 S:	Maintained
 F:	include/linux/shmem_fs.h
 F:	mm/shmem.c