feat(backups-cli): create-symlink-index command

```
> xo-backups create-symlink-indexes ./xo-vm-backups vm.name_label
> ls ./xo-vm-backups/indexes/vm.name_label
Debian\ 9.5\ 64bit\ web9 -> ../../c60dc26a-49e8-be58-6ae4-175cf03b19d5/
Prod\ VM -> ../../1498796a-3d23-d0cc-74be-b25d6e598c03/
```

@xen-orchestra/backups-cli/_fs.js

@@ -1,6 +1,25 @@
+const { dirname } = require('path')
+
 const fs = require('promise-toolbox/promisifyAll')(require('fs'))
 module.exports = fs
 
+fs.mktree = async function mkdirp(path) {
+  try {
+    await fs.mkdir(path)
+  } catch (error) {
+    const { code } = error
+    if (code === 'EEXIST') {
+      await fs.readdir(path)
+      return
+    }
+    if (code === 'ENOENT') {
+      await mkdirp(dirname(path))
+      return mkdirp(path)
+    }
+    throw error
+  }
+}
+
 // - easier:
 //   - single param for direct use in `Array#map`
 //   - files are prefixed with directory path
@@ -25,3 +44,14 @@ fs.readdir2 = path =>
       throw error
     }
   )
+
+fs.symlink2 = async (target, path) => {
+  try {
+    await fs.symlink(target, path)
+  } catch (error) {
+    if (error.code === 'EEXIST' && (await fs.readlink(path)) === target) {
+      return
+    }
+    throw error
+  }
+}

@xen-orchestra/backups-cli/commands/create-symlink-index.js

@@ -0,0 +1,28 @@
+const filenamify = require('filenamify')
+const get = require('lodash/get')
+const { dirname, join, relative } = require('path')
+
+const asyncMap = require('../_asyncMap')
+const { mktree, readdir2, readFile, symlink2 } = require('../_fs')
+
+module.exports = async function createSymlinkIndex([backupDir, fieldPath]) {
+  const indexDir = join(backupDir, 'indexes', filenamify(fieldPath))
+  await mktree(indexDir)
+
+  await asyncMap(await readdir2(backupDir), async vmDir =>
+    asyncMap(
+      (await readdir2(vmDir)).filter(_ => _.endsWith('.json')),
+      async json => {
+        const metadata = JSON.parse(await readFile(json))
+        const value = get(metadata, fieldPath)
+        if (value !== undefined) {
+          const target = relative(indexDir, dirname(json))
+          const path = join(indexDir, filenamify(String(value)))
+          await symlink2(target, path).catch(error => {
+            console.warn('symlink(%s, %s)', target, path, error)
+          })
+        }
+      }
+    )
+  )
+}

@xen-orchestra/backups-cli/index.js

@@ -7,6 +7,12 @@ require('./_composeCommands')({
     },
     usage: '[--force] xo-vm-backups/*',
   },
+  'create-symlink-index': {
+    get main() {
+      return require('./commands/create-symlink-index')
+    },
+    usage: 'xo-vm-backups <field path>',
+  },
 })(process.argv.slice(2), 'xo-backups').catch(error => {
   console.error('main', error)
   process.exitCode = 1

@xen-orchestra/backups-cli/package.json

@@ -5,6 +5,7 @@
   "bugs": "https://github.com/vatesfr/xen-orchestra/issues",
   "dependencies": {
     "@xen-orchestra/fs": "^0.10.2",
+    "filenamify": "^4.1.0",
     "getopts": "^2.2.5",
     "lodash": "^4.17.15",
     "promise-toolbox": "^0.14.0",

yarn.lock

@@ -6112,6 +6112,20 @@ filename-regex@^2.0.0:
   resolved "https://registry.yarnpkg.com/filename-regex/-/filename-regex-2.0.1.tgz#c1c4b9bee3e09725ddb106b75c1e301fe2f18b26"
   integrity sha1-wcS5vuPglyXdsQa3XB4wH+LxiyY=
 
+filename-reserved-regex@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/filename-reserved-regex/-/filename-reserved-regex-2.0.0.tgz#abf73dfab735d045440abfea2d91f389ebbfa229"
+  integrity sha1-q/c9+rc10EVECr/qLZHzieu/oik=
+
+filenamify@^4.1.0:
+  version "4.1.0"
+  resolved "https://registry.yarnpkg.com/filenamify/-/filenamify-4.1.0.tgz#54d110810ae74eebfe115c1b995bd07e03cf2184"
+  integrity sha512-KQV/uJDI9VQgN7sHH1Zbk6+42cD6mnQ2HONzkXUfPJ+K2FC8GZ1dpewbbHw0Sz8Tf5k3EVdHVayM4DoAwWlmtg==
+  dependencies:
+    filename-reserved-regex "^2.0.0"
+    strip-outer "^1.0.1"
+    trim-repeated "^1.0.0"
+
 fill-range@^2.1.0:
   version "2.2.4"
   resolved "https://registry.yarnpkg.com/fill-range/-/fill-range-2.2.4.tgz#eb1e773abb056dcd8df2bfdf6af59b8b3a936565"
@@ -13605,6 +13619,13 @@ strip-json-comments@~2.0.1:
   resolved "https://registry.yarnpkg.com/strip-json-comments/-/strip-json-comments-2.0.1.tgz#3c531942e908c2697c0ec344858c286c7ca0a60a"
   integrity sha1-PFMZQukIwml8DsNEhYwobHygpgo=
 
+strip-outer@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/strip-outer/-/strip-outer-1.0.1.tgz#b2fd2abf6604b9d1e6013057195df836b8a9d631"
+  integrity sha512-k55yxKHwaXnpYGsOzg4Vl8+tDrWylxDEpknGjhTiZB8dFRU5rTo9CAzeycivxV3s+zlTKwrs6WxMxR95n26kwg==
+  dependencies:
+    escape-string-regexp "^1.0.2"
+
 struct-fu@^1.2.0, struct-fu@^1.2.1:
   version "1.2.1"
   resolved "https://registry.yarnpkg.com/struct-fu/-/struct-fu-1.2.1.tgz#1b8920bf44b669914e969393de51bb2e920be551"
@@ -14013,6 +14034,13 @@ trim-newlines@^1.0.0:
   resolved "https://registry.yarnpkg.com/trim-newlines/-/trim-newlines-1.0.0.tgz#5887966bb582a4503a41eb524f7d35011815a613"
   integrity sha1-WIeWa7WCpFA6QetST301ARgVphM=
 
+trim-repeated@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/trim-repeated/-/trim-repeated-1.0.0.tgz#e3646a2ea4e891312bf7eace6cfb05380bc01c21"
+  integrity sha1-42RqLqTokTEr9+rObPsFOAvAHCE=
+  dependencies:
+    escape-string-regexp "^1.0.2"
+
 trim-right@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/trim-right/-/trim-right-1.0.1.tgz#cb2e1203067e0c8de1f614094b9fe45704ea6003"