m/pkg/pstore: add package to interface with pstore

This adds a package for interfacing with the Linux kernel's pstore
(persistent storage) system. Currently only handles kmsg/dmesg-type logs
as mce has an unknown format and I have no examples.

Change-Id: I3089a53cdca224c7e6e04dd51a94035d7b2b880b
Reviewed-on: https://review.monogon.dev/c/monogon/+/769
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/pkg/pstore/pstore_test.go b/metropolis/pkg/pstore/pstore_test.go
new file mode 100644
index 0000000..0190f04
--- /dev/null
+++ b/metropolis/pkg/pstore/pstore_test.go
@@ -0,0 +1,144 @@
+package pstore
+
+import (
+	"fmt"
+	"testing"
+	"testing/fstest"
+	"time"
+)
+
+func TestParseHeader(t *testing.T) {
+	var cases = []struct {
+		input       string
+		expectedOut *pstoreDmesgHeader
+	}{
+		{"Panic#2 Part30", &pstoreDmesgHeader{"Panic", 2, 30}},
+		{"Oops#1 Part5", &pstoreDmesgHeader{"Oops", 1, 5}},
+		// Random kernel output that is similar, but definitely not a dump header
+		{"<4>[2501503.489317] Oops: 0010 [#1] SMP NOPTI", nil},
+	}
+	for i, c := range cases {
+		t.Run(fmt.Sprintf("Test#%d", i+1), func(t *testing.T) {
+			out, err := parseDmesgHeader(c.input)
+			switch {
+			case err != nil && c.expectedOut != nil:
+				t.Errorf("Failed parsing %q: %v", c.input, err)
+			case err == nil && c.expectedOut == nil:
+				t.Errorf("Successfully parsed %q, expected error", c.input)
+			case err != nil && c.expectedOut == nil:
+			case err == nil && c.expectedOut != nil:
+				if out.Part != c.expectedOut.Part {
+					t.Errorf("Expected part to be %d, got %d", c.expectedOut.Part, out.Part)
+				}
+				if out.Counter != c.expectedOut.Counter {
+					t.Errorf("Expected counter to be %d, got %d", c.expectedOut.Counter, out.Counter)
+				}
+				if out.Reason != c.expectedOut.Reason {
+					t.Errorf("Expected reason to be %q, got %q", c.expectedOut.Reason, out.Reason)
+				}
+			}
+		})
+	}
+}
+
+func TestGetKmsgDumps(t *testing.T) {
+	testTime1 := time.Date(2022, 06, 13, 1, 2, 3, 4, time.UTC)
+	testTime2 := time.Date(2020, 06, 13, 1, 2, 3, 4, time.UTC)
+	testTime3 := time.Date(2010, 06, 13, 1, 2, 3, 4, time.UTC)
+	cases := []struct {
+		name          string
+		inputFS       fstest.MapFS
+		expectErr     bool
+		expectedDumps []KmsgDump
+	}{
+		{"EmptyPstore", map[string]*fstest.MapFile{}, false, []KmsgDump{}},
+		{"SingleDumpSingleFile", map[string]*fstest.MapFile{
+			"dmesg-efi-165467917816002": {ModTime: testTime1, Data: []byte("Panic#2 Part1\ntest1\ntest2")},
+			"yolo-efi-165467917816002":  {ModTime: testTime1, Data: []byte("something totally unrelated")},
+		}, false, []KmsgDump{{
+			Reason:     "Panic",
+			OccurredAt: testTime1,
+			Counter:    2,
+			Lines: []string{
+				"test1",
+				"test2",
+			},
+		}}},
+		{"SingleDumpMultipleFiles", map[string]*fstest.MapFile{
+			"dmesg-efi-165467917816002": {ModTime: testTime1, Data: []byte("Panic#2 Part1\ntest2\ntest3")},
+			"dmesg-efi-165467917817002": {ModTime: testTime2, Data: []byte("Panic#2 Part2\ntest1")},
+		}, false, []KmsgDump{{
+			Reason:     "Panic",
+			OccurredAt: testTime1,
+			Counter:    2,
+			Lines: []string{
+				"test1",
+				"test2",
+				"test3",
+			},
+		}}},
+		{"MultipleDumpsMultipleFiles", map[string]*fstest.MapFile{
+			"dmesg-efi-165467917816002": {ModTime: testTime1, Data: []byte("Panic#2 Part1\ntest2\ntest3")},
+			"dmesg-efi-165467917817002": {ModTime: testTime2, Data: []byte("Panic#2 Part2\ntest1")},
+			"dmesg-efi-265467917816002": {ModTime: testTime3, Data: []byte("Oops#1 Part1\noops3")},
+			"dmesg-efi-265467917817002": {ModTime: testTime2, Data: []byte("Oops#1 Part2\noops1\noops2")},
+		}, false, []KmsgDump{{
+			Reason:     "Panic",
+			OccurredAt: testTime1,
+			Counter:    2,
+			Lines: []string{
+				"test1",
+				"test2",
+				"test3",
+			},
+		}, {
+			Reason:     "Oops",
+			OccurredAt: testTime3,
+			Counter:    1,
+			Lines: []string{
+				"oops1",
+				"oops2",
+				"oops3",
+			},
+		}}},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			dumps, err := getKmsgDumpsFromFS(c.inputFS)
+			switch {
+			case err == nil && c.expectErr:
+				t.Error("Expected error, but got none")
+				return
+			case err != nil && !c.expectErr:
+				t.Errorf("Got unexpected error: %v", err)
+				return
+			case err != nil && c.expectErr:
+				// Got expected error
+				return
+			case err == nil && !c.expectErr:
+				if len(dumps) != len(c.expectedDumps) {
+					t.Fatalf("Expected %d dumps, got %d", len(c.expectedDumps), len(dumps))
+				}
+				for i, dump := range dumps {
+					if dump.OccurredAt != c.expectedDumps[i].OccurredAt {
+						t.Errorf("Dump %d expected to have occurred at %v, got %v", i, c.expectedDumps[i].OccurredAt, dump.OccurredAt)
+					}
+					if dump.Reason != c.expectedDumps[i].Reason {
+						t.Errorf("Expected reason in dump %d to be %v, got %v", i, c.expectedDumps[i].Reason, dump.Reason)
+					}
+					if dump.Counter != c.expectedDumps[i].Counter {
+						t.Errorf("Expected counter in dump %d to be %d, got %d", i, c.expectedDumps[i].Counter, dump.Counter)
+					}
+					if len(dump.Lines) != len(c.expectedDumps[i].Lines) {
+						t.Errorf("Expected number of lines in dump %d to be %d, got %d", i, len(c.expectedDumps[i].Lines), len(dump.Lines))
+					}
+					for j := range dump.Lines {
+						if dump.Lines[j] != c.expectedDumps[i].Lines[j] {
+							t.Errorf("Expected line %d in dump %d to be %q, got %q", i, j, c.expectedDumps[i].Lines[j], dump.Lines[j])
+						}
+					}
+				}
+			}
+		})
+	}
+}