feat(vhd-lib/mergeVhd): continuable (#5749)

packages/vhd-lib/src/merge.js

@@ -3,10 +3,14 @@
 import assert from 'assert'
 import concurrency from 'limit-concurrency-decorator'
 import noop from './_noop'
+import { createLogger } from '@xen-orchestra/log'
 
 import Vhd from './vhd'
+import { basename, dirname } from 'path'
 import { DISK_TYPE_DIFFERENCING, DISK_TYPE_DYNAMIC } from './_constants'
 
+const { warn } = createLogger('vhd-lib:merge')
+
 // Merge vhd child into vhd parent.
 //
 // TODO: rename the VHD file during the merge
@@ -17,6 +21,8 @@ export default concurrency(2)(async function merge(
   childPath,
   { onProgress = noop } = {}
 ) {
+  const mergeStatePath = dirname(parentPath) + '/' + '.' + basename(parentPath) + '.merge.json'
+
   const parentFd = await parentHandler.openFile(parentPath, 'r+')
   try {
     const parentVhd = new Vhd(parentHandler, parentFd)
@@ -24,31 +30,61 @@ export default concurrency(2)(async function merge(
     try {
       const childVhd = new Vhd(childHandler, childFd)
 
+      let mergeState = await parentHandler.readFile(mergeStatePath).catch(error => {
+        if (error.code !== 'ENOENT') {
+          throw error
+        }
+        // no merge state in case of missing file
+      })
+
       // Reading footer and header.
-      await Promise.all([parentVhd.readHeaderAndFooter(), childVhd.readHeaderAndFooter()])
+      await Promise.all([
+        parentVhd.readHeaderAndFooter(
+          // dont check VHD is complete if recovering a merge
+          mergeState === undefined
+        ),
 
-      assert(childVhd.header.blockSize === parentVhd.header.blockSize)
+        childVhd.readHeaderAndFooter(),
+      ])
 
-      const parentDiskType = parentVhd.footer.diskType
-      assert(parentDiskType === DISK_TYPE_DIFFERENCING || parentDiskType === DISK_TYPE_DYNAMIC)
-      assert.strictEqual(childVhd.footer.diskType, DISK_TYPE_DIFFERENCING)
+      if (mergeState !== undefined) {
+        mergeState = JSON.parse(mergeState)
+
+        // ensure the correct merge will be continued
+        assert.strictEqual(parentVhd.header.checksum, mergeState.parent.header)
+        assert.strictEqual(childVhd.header.checksum, mergeState.child.header)
+      } else {
+        assert.strictEqual(childVhd.header.blockSize, parentVhd.header.blockSize)
+
+        const parentDiskType = parentVhd.footer.diskType
+        assert(parentDiskType === DISK_TYPE_DIFFERENCING || parentDiskType === DISK_TYPE_DYNAMIC)
+        assert.strictEqual(childVhd.footer.diskType, DISK_TYPE_DIFFERENCING)
+      }
 
       // Read allocation table of child/parent.
       await Promise.all([parentVhd.readBlockAllocationTable(), childVhd.readBlockAllocationTable()])
 
       const { maxTableEntries } = childVhd.header
 
-      await parentVhd.ensureBatSize(childVhd.header.maxTableEntries)
+      if (mergeState === undefined) {
+        await parentVhd.ensureBatSize(childVhd.header.maxTableEntries)
 
-      // finds first allocated block for the 2 following loops
-      let firstBlock = 0
-      while (firstBlock < maxTableEntries && !childVhd.containsBlock(firstBlock)) {
-        ++firstBlock
+        mergeState = {
+          child: { header: childVhd.header.checksum },
+          parent: { header: parentVhd.header.checksum },
+          currentBlock: 0,
+          mergedDataSize: 0,
+        }
+
+        // finds first allocated block for the 2 following loops
+        while (mergeState.currentBlock < maxTableEntries && !childVhd.containsBlock(mergeState.currentBlock)) {
+          ++mergeState.currentBlock
+        }
       }
 
       // counts number of allocated blocks
       let nBlocks = 0
-      for (let block = firstBlock; block < maxTableEntries; block++) {
+      for (let block = mergeState.currentBlock; block < maxTableEntries; block++) {
         if (childVhd.containsBlock(block)) {
           nBlocks += 1
         }
@@ -57,13 +93,14 @@ export default concurrency(2)(async function merge(
       onProgress({ total: nBlocks, done: 0 })
 
       // merges blocks
-      let mergedDataSize = 0
-      for (let i = 0, block = firstBlock; i < nBlocks; ++i, ++block) {
-        while (!childVhd.containsBlock(block)) {
-          ++block
+      for (let i = 0; i < nBlocks; ++i, ++mergeState.currentBlock) {
+        while (!childVhd.containsBlock(mergeState.currentBlock)) {
+          ++mergeState.currentBlock
         }
 
-        mergedDataSize += await parentVhd.coalesceBlock(childVhd, block)
+        await parentHandler.writeFile(mergeStatePath, JSON.stringify(mergeState), { flags: 'w' }).catch(warn)
+
+        mergeState.mergedDataSize += await parentVhd.coalesceBlock(childVhd, mergeState.currentBlock)
         onProgress({
           total: nBlocks,
           done: i + 1,
@@ -83,11 +120,12 @@ export default concurrency(2)(async function merge(
       // creation
       await parentVhd.writeFooter()
 
-      return mergedDataSize
+      return mergeState.mergedDataSize
     } finally {
       await childHandler.closeFile(childFd)
     }
   } finally {
+    parentHandler.unlink(mergeStatePath).catch(warn)
     await parentHandler.closeFile(parentFd)
   }
 })