Merge pull request #11 from AkihiroSuda/dev

Fix random read

Author: AkihiroSuda

hack/compare-with-qemu-img.sh

@@ -14,6 +14,7 @@ set -x
 go-qcow2reader-example -info "${name_qcow2}"
 set +x
 
+echo "===== Phase 1: full read ====="
 if [ ! -e "${name_raw_a}" ]; then
 	echo "Converting ${name_qcow2} to ${name_raw_a} with qemu-img"
 	set -x
@@ -46,7 +47,26 @@ else
 	exit 1
 fi
 
-echo "Cleaning up..."
+echo "===== Phase 2: random read ====="
+for offset in 1 22 333 4444 55555 666666 7777777 88888888; do
+	for length in 1 22 333 4444 55555 666666 7777777 88888888; do
+		set -x
+		set +o pipefail
+		expected="$(tail -c "+$((${offset} + 1))" "${name_raw_a}" | head -c "${length}" | sha256sum - | cut -d " " -f 1)"
+		set -o pipefail
+		got="$(go-qcow2reader-example -offset="${offset}" -length="${length}" "${name_qcow2}" | sha256sum - | cut -d " " -f 1)"
+		set +x
+		echo "Comparing: ${expected} vs ${got}"
+		if [ "${expected}" = "${got}" ]; then
+			echo "OK"
+		else
+			echo "FAIL"
+			exit 1
+		fi
+	done
+done
+
+echo "===== Cleaning up... ====="
 set -x
 rm -f "${name_raw_b}" "${name_raw_b}.sha256"
 set +x

image/qcow2/qcow2.go

@@ -802,10 +802,17 @@ func (img *Qcow2) readAtAlignedStandardExtendedL2(p []byte, off int64, desc stan
 	var n int
 	subclusterSize := img.clusterSize / 32
 	hostClusterOffset := desc.hostClusterOffset()
-	subclusterNo := (int(off) % img.clusterSize) / subclusterSize
-	for i := subclusterNo; i < 32; i++ {
+	subclusterNoBegin := (int(off) % img.clusterSize) / subclusterSize
+	for i := subclusterNoBegin; i < 32; i++ { // i is the subcluster number
+		currentOff := off + int64(n)
+		clusterNo := currentOff / int64(img.clusterSize)
+		clusterBegin := clusterNo * int64(img.clusterSize)
+		subclusterBegin := clusterBegin + int64(i)*int64(subclusterSize)
+		subclusterEnd := subclusterBegin + int64(subclusterSize)
+		readSize := subclusterEnd - currentOff
+
 		pIdxBegin := n
-		pIdxEnd := n + subclusterSize
+		pIdxEnd := n + int(readSize)
 		if pIdxEnd > len(p) {
 			pIdxEnd = len(p)
 		}
@@ -823,7 +830,6 @@ func (img *Qcow2) readAtAlignedStandardExtendedL2(p []byte, off int64, desc stan
 				return n, fmt.Errorf("failed to read from the raw offset %d: %w", currentRawOff, err)
 			}
 		} else {
-			currentOff := off + int64(n)
 			if ((extL2Entry.ZeroStatusBitmap >> i) & 0b1) == 0b1 {
 				currentN, err = img.readZero(p[pIdxBegin:pIdxEnd], currentOff)
 				if err != nil {
@@ -902,15 +908,13 @@ func (img *Qcow2) ReadAt(p []byte, off int64) (n int, err error) {
 
 	for remaining > 0 {
 		currentOff := off + int64(n)
-		pIndexBegin := n
-		pIndexEnd := n + int(img.clusterSize)
-
-		clusterBegin := (off + int64(pIndexBegin)) / int64(img.clusterSize)
-		if clusterEnd := (off + int64(pIndexEnd)) / int64(img.clusterSize); clusterEnd != clusterBegin {
-			currentSize := off + int64(img.clusterSize) - int64(n)
-			pIndexEnd = pIndexBegin + int(currentSize)
-		}
+		clusterNo := currentOff / int64(img.clusterSize)
+		clusterBegin := clusterNo * int64(img.clusterSize)
+		clusterEnd := clusterBegin + int64(img.clusterSize)
+		readSize := clusterEnd - currentOff
 
+		pIndexBegin := n
+		pIndexEnd := n + int(readSize)
 		if pIndexEnd > len(p) {
 			pIndexEnd = len(p)
 		}