Add occ preview:migrate to migrate previews from the old flat structure to a subfolder structure

* `php occ preview:repair` - a preview migration tool that moves existing previews into the new location introduced with #19214
* moves `appdata_INSTANCEID/previews/FILEID` to `appdata_INSTANCEID/previews/0/5/8/4/c/e/5/FILEID`
* migration tool can be stopped during migration via `CTRL+C` - it then finishes the current folder (with the previews of one file) and stops gracefully
* if a PHP memory limit is set in the `php.ini` then it will stop automatically once it has less than 25 MiB memory left (this is to avoid hard crashes in the middle of a migration)
* the tool can be used during operation - possible drawbacks:
    * there is the chance of a race condition that a new preview is generated in the moment the folder is already migrated away - so the old folder with the newly cached preview is deleted and one cached preview needs to be re-generated
    * there is the chance of a race condition during access of a preview while it is migrated to the other folder - then no preview can be shown and results in a 404 (as of now this is an accepted risk)

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/core/register_command.php b/core/register_command.php
index d818423d1ab..03d458a9cbc 100644
--- a/core/register_command.php
+++ b/core/register_command.php
@@ -155,6 +155,8 @@ if (\OC::$server->getConfig()->getSystemValue('installed', false)) {
 		\OC::$server->getAppManager()
 	));
 
+	$application->add(\OC::$server->query(\OC\Core\Command\Preview\Repair::class));
+
 	$application->add(new OC\Core\Command\User\Add(\OC::$server->getUserManager(), \OC::$server->getGroupManager()));
 	$application->add(new OC\Core\Command\User\Delete(\OC::$server->getUserManager()));
 	$application->add(new OC\Core\Command\User\Disable(\OC::$server->getUserManager()));