openfiletable: add inummap

Generates unique inode numbers for files on different
devices.

https://github.com/rfjakob/gocryptfs/issues/435

1 files changed, 63 insertions, 0 deletions

diff --git a/internal/openfiletable/inummap.go b/internal/openfiletable/inummap.go
new file mode 100644
index 0000000..d9f6862
--- /dev/null
+++ b/internal/openfiletable/inummap.go
@@ -0,0 +1,63 @@
+package openfiletable
+
+import (
+	"sync"
+	"syscall"
+)
+
+// UINT64_MAX           = 18446744073709551615
+const inumTranslateBase = 10000000000000000000
+
+// InumMap ... see NewInumMap() for description.
+type InumMap struct {
+	sync.Mutex
+	baseDev       uint64
+	translate     map[QIno]uint64
+	translateNext uint64
+}
+
+// NewInumMap returns a new inumMap.
+//
+// inumMap 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 NewInumMap(baseDev uint64) *InumMap {
+	return &InumMap{
+		baseDev:       baseDev,
+		translate:     make(map[QIno]uint64),
+		translateNext: inumTranslateBase,
+	}
+}
+
+// Translate maps the passed-in (device, inode) pair to a unique inode number.
+func (m *InumMap) 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 *InumMap) 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 *InumMap) Count() int {
+	return len(m.translate)
+}