try to use copy_file_range for VHD merge

@xen-orchestra/fs/package.json

@@ -36,6 +36,7 @@
     "readable-stream": "^3.0.6",
     "through2": "^4.0.2",
     "tmp": "^0.2.1",
+    "syscall": "^0.2.0",
     "xo-remote-parser": "^0.6.0"
   },
   "devDependencies": {

@xen-orchestra/fs/src/_mount.js

@@ -1,14 +1,22 @@
 import execa from 'execa'
 import fs from 'fs-extra'
-import { ignoreErrors } from 'promise-toolbox'
+import { ignoreErrors, fromCallback } from 'promise-toolbox'
 import { join } from 'path'
 import { tmpdir } from 'os'
 
 import LocalHandler from './local'
+import { Syscall6 } from 'syscall'
+import normalizePath from './_normalizePath'
+import { randomBytes } from 'crypto'
 
 const sudoExeca = (command, args, opts) =>
   execa('sudo', [command, ...args], opts)
 
+const computeRate = (hrtime: number[], size: number) => {
+  const seconds = hrtime[0] + hrtime[1] / 1e9
+  return size / seconds
+}
+
 export default class MountHandler extends LocalHandler {
   constructor(
     remote,
@@ -56,6 +64,71 @@ export default class MountHandler extends LocalHandler {
     return this._realPath
   }
 
+  async test(): Promise<Object> {
+    /**
+     * @returns the number of byte effectively copied, needs to be called in a loop!
+     */
+    function copy_file_range(fdIn, offsetIn, fdOut, offsetOut, dataLen, flags = 0) {
+      // we are stuck on linux x86_64
+      function wrapOffset(offsetIn) {
+        if (offsetIn == null)
+          return 0
+        const offsetInBuffer = new Uint32Array(2)
+        new DataView(offsetInBuffer.buffer).setBigUint64(0, BigInt(offsetIn), true)
+        return offsetInBuffer
+      }
+
+      const SYS_copy_file_range = 326
+      const [ret, _, errno] = Syscall6(SYS_copy_file_range, fdIn, wrapOffset(offsetIn), fdOut, wrapOffset(offsetOut), data.byteLength, 0)
+      if (errno !== 0) {
+        throw new Error('Error no', errno)
+      }
+      return ret
+    }
+
+    const SIZE = 1024 * 1024 * 10
+    const testFileName = normalizePath(`${Date.now()}.test`)
+    const testFileName2 = normalizePath(`${Date.now()}__2.test`)
+    const data = await fromCallback(randomBytes, SIZE)
+    let step = 'write'
+    try {
+      const writeStart = process.hrtime()
+      await this._outputFile(testFileName, data, { flags: 'wx' })
+      const writeDuration = process.hrtime(writeStart)
+      step = 'duplicate'
+      const fd1 = await this._openFile(testFileName, 'r')
+      const fd2 = await this._openFile(testFileName2, 'w')
+      console.log('_openFile', fd1, fd2, data.byteLength)
+
+      const res = copy_file_range(fd1, 0, fd2, null, data.byteLength, 0)
+      console.log('copy_file_range', res)
+      await this._closeFile(fd2)
+
+      step = 'read'
+      const readStart = process.hrtime()
+      const read = await this._readFile(testFileName, { flags: 'r' })
+      const readDuration = process.hrtime(readStart)
+
+      if (!data.equals(read)) {
+        throw new Error('output and input did not match')
+      }
+      return {
+        success: true,
+        writeRate: computeRate(writeDuration, SIZE),
+        readRate: computeRate(readDuration, SIZE),
+      }
+    } catch (error) {
+      return {
+        success: false,
+        step,
+        file: testFileName,
+        error: error.message || String(error),
+      }
+    } finally {
+      ignoreErrors.call(this._unlink(testFileName))
+    }
+  }
+
   async _sync() {
     // in case of multiple `sync`s, ensure we properly close previous keeper
     {

yarn.lock

@@ -3974,7 +3974,7 @@ bind-property-descriptor@^1.0.0:
   dependencies:
     lodash "^4.17.4"
 
-bindings@^1.5.0:
+bindings@^1.3.0, bindings@^1.5.0:
   version "1.5.0"
   resolved "https://registry.yarnpkg.com/bindings/-/bindings-1.5.0.tgz#10353c9e945334bc0511a6d90b38fbc7c9c504df"
   integrity sha512-p2q/t/mhvuOj/UeLlV6566GD/guowlr0hHxClI0W9m7MWYkL1F0hLo+0Aexs9HSPCtR1SXQ0TD3MMKrXZajbiQ==
@@ -12784,7 +12784,7 @@ node-gyp-build@~4.1.0:
   resolved "https://registry.yarnpkg.com/node-gyp-build/-/node-gyp-build-4.1.1.tgz#d7270b5d86717068d114cc57fff352f96d745feb"
   integrity sha512-dSq1xmcPDKPZ2EED2S6zw/b9NKsqzXRE6dVr8TVQnI3FJOTteUMuqF3Qqs6LZg+mLGYJWqQzMbIjMtJqTv87nQ==
 
-node-gyp@^3.8.0:
+node-gyp@^3.7.0, node-gyp@^3.8.0:
   version "3.8.0"
   resolved "https://registry.yarnpkg.com/node-gyp/-/node-gyp-3.8.0.tgz#540304261c330e80d0d5edce253a68cb3964218c"
   integrity sha512-3g8lYefrRRzvGeSowdJKAKyks8oUpLEd/DyPV4eMhVlhJ0aNaZqIrNUIPuEWWTAoPqyFkfGrM67MC69baqn6vA==
@@ -17313,6 +17313,14 @@ syntax-error@^1.1.1:
   dependencies:
     acorn-node "^1.2.0"
 
+syscall@^0.2.0:
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/syscall/-/syscall-0.2.0.tgz#9308898495dfb5c062ea7a60c46f81f29f532ac4"
+  integrity sha512-MLlgaLAMbOGKUVlqsLVYnJ4dBZmeE1nza4BVgVgGUr2dPV17tgR79JUPIUybX/EqGm1jywsXSXUPXpNbIXDVCw==
+  dependencies:
+    bindings "^1.3.0"
+    node-gyp "^3.7.0"
+
 table@^5.2.3:
   version "5.4.6"
   resolved "https://registry.yarnpkg.com/table/-/table-5.4.6.tgz#1292d19500ce3f86053b05f0e8e7e4a3bb21079e"