reverse: add single-entry path cache

Speeds up the "ls -lR" benchmark from 2.6 seconds to 2.0.

1 files changed, 41 insertions, 0 deletions

diff --git a/internal/fusefrontend_reverse/rpath_cache.go b/internal/fusefrontend_reverse/rpath_cache.go
new file mode 100644
index 0000000..81e945b
--- /dev/null
+++ b/internal/fusefrontend_reverse/rpath_cache.go
@@ -0,0 +1,41 @@
+package fusefrontend_reverse
+
+import (
+	"sync"
+)
+
+// rPathCacheContainer is a simple one entry path cache. Because the dirIV
+// is generated deterministically from the directory path, there is no need
+// to ever invalidate entries.
+type rPathCacheContainer struct {
+	sync.Mutex
+	// Relative ciphertext path to the directory
+	cPath string
+	// Relative plaintext path
+	pPath string
+	// Directory IV of the directory
+	dirIV []byte
+}
+
+func (c *rPathCacheContainer) lookup(cPath string) ([]byte, string) {
+	c.Lock()
+	defer c.Unlock()
+	if cPath == c.cPath {
+		//fmt.Printf("HIT   %q\n", cPath)
+		return c.dirIV, c.pPath
+	}
+	//fmt.Printf("MISS  %q\n", cPath)
+	return nil, ""
+}
+
+// store - write entry for "cPath" into the cache
+func (c *rPathCacheContainer) store(cPath string, dirIV []byte, pPath string) {
+	//fmt.Printf("STORE %q\n", cPath)
+	c.Lock()
+	defer c.Unlock()
+	c.cPath = cPath
+	c.dirIV = dirIV
+	c.pPath = pPath
+}
+
+var rPathCache rPathCacheContainer