3 files changed, 169 insertions, 0 deletions
diff --git a/internal/inomap/inomap.go b/internal/inomap/inomap.go
new file mode 100644
index 0000000..f8909c7
--- /dev/null
+++ b/internal/inomap/inomap.go
@@ -0,0 +1,63 @@
+package inomap
+
+import (
+	"sync"
+	"syscall"
+)
+
+// UINT64_MAX           = 18446744073709551615
+const inumTranslateBase = 10000000000000000000
+
+// InoMap ... see New() for description.
+type InoMap struct {
+	sync.Mutex
+	baseDev       uint64
+	translate     map[QIno]uint64
+	translateNext uint64
+}
+
+// New returns a new InoMap.
+//
+// InoMap translates (device uint64, inode uint64) pairs to unique uint64
+// inode numbers.
+// Inode numbers on the "baseDev" are passed through unchanged (as long as they
+// are not higher than inumTranslateBase).
+// Inode numbers on other devices are remapped to the number space above
+// 10000000000000000000. The mapping is stored in a simple Go map. Entries
+// can only be added and are never removed.
+func New(baseDev uint64) *InoMap {
+	return &InoMap{
+		baseDev:       baseDev,
+		translate:     make(map[QIno]uint64),
+		translateNext: inumTranslateBase,
+	}
+}
+
+// Translate maps the passed-in (device, inode) pair to a unique inode number.
+func (m *InoMap) Translate(in QIno) (out uint64) {
+	if in.Dev == m.baseDev && in.Ino < inumTranslateBase {
+		return in.Ino
+	}
+	m.Lock()
+	defer m.Unlock()
+	out = m.translate[in]
+	if out != 0 {
+		return out
+	}
+	out = m.translateNext
+	m.translate[in] = m.translateNext
+	m.translateNext++
+	return out
+}
+
+// TranslateStat translates the inode number contained in "st" if neccessary.
+// Convience wrapper around Translate().
+func (m *InoMap) TranslateStat(st *syscall.Stat_t) {
+	in := QInoFromStat(st)
+	st.Ino = m.Translate(in)
+}
+
+// Count returns the number of entries in the translation table.
+func (m *InoMap) Count() int {
+	return len(m.translate)
+}
diff --git a/internal/inomap/inomap_test.go b/internal/inomap/inomap_test.go
new file mode 100644
index 0000000..3c0ea7d
--- /dev/null
+++ b/internal/inomap/inomap_test.go
@@ -0,0 +1,81 @@
+package inomap
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestTranslate(t *testing.T) {
+	const baseDev = 12345
+	m := New(baseDev)
+
+	q := QIno{Dev: baseDev, Ino: 1}
+	out := m.Translate(q)
+	if out != 1 {
+		t.Errorf("expected 1, got %d", out)
+	}
+	q.Ino = inumTranslateBase
+	out = m.Translate(q)
+	if out < inumTranslateBase {
+		t.Errorf("got %d", out)
+	}
+	out2 := m.Translate(q)
+	if out2 != out {
+		t.Errorf("unstable mapping: %d %d", out2, out)
+	}
+}
+
+func TestTranslateStress(t *testing.T) {
+	const baseDev = 12345
+	m := New(baseDev)
+	var wg sync.WaitGroup
+	wg.Add(4)
+	go func() {
+		q := QIno{Dev: baseDev}
+		for i := uint64(1); i <= 10000; i++ {
+			q.Ino = i
+			out := m.Translate(q)
+			if out != i {
+				t.Fail()
+			}
+		}
+		wg.Done()
+	}()
+	go func() {
+		q := QIno{Dev: baseDev}
+		for i := uint64(1); i <= 10000; i++ {
+			q.Ino = inumTranslateBase + i
+			out := m.Translate(q)
+			if out < inumTranslateBase {
+				t.Fail()
+			}
+		}
+		wg.Done()
+	}()
+	go func() {
+		q := QIno{Dev: 9999999}
+		for i := uint64(1); i <= 10000; i++ {
+			q.Ino = i
+			out := m.Translate(q)
+			if out < inumTranslateBase {
+				t.Fail()
+			}
+		}
+		wg.Done()
+	}()
+	go func() {
+		q := QIno{Dev: 4444444}
+		for i := uint64(1); i <= 10000; i++ {
+			q.Ino = i
+			out := m.Translate(q)
+			if out < inumTranslateBase {
+				t.Fail()
+			}
+		}
+		wg.Done()
+	}()
+	wg.Wait()
+	if m.Count() != 30000 {
+		t.Fail()
+	}
+}
diff --git a/internal/inomap/qino.go b/internal/inomap/qino.go
new file mode 100644
index 0000000..8f99004
--- /dev/null
+++ b/internal/inomap/qino.go
@@ -0,0 +1,25 @@
+package inomap
+
+import (
+	"syscall"
+)
+
+// QIno = Qualified Inode number.
+// Uniquely identifies a backing file through the device number,
+// inode number pair.
+type QIno struct {
+	// Stat_t.{Dev,Ino} is uint64 on 32- and 64-bit Linux
+	Dev uint64
+	Ino uint64
+}
+
+// QInoFromStat fills a new QIno struct with the passed Stat_t info.
+func QInoFromStat(st *syscall.Stat_t) QIno {
+	return QIno{
+		// There are some architectures that use 32-bit values here
+		// (darwin, freebsd-32, maybe others). Add and explicit cast to make
+		// this function work everywhere.
+		Dev: uint64(st.Dev),
+		Ino: uint64(st.Ino),
+	}
+}