Check available space in /var/lib/postgresql before running postgresql migration

locales/en.json

@@ -242,6 +242,7 @@
     "migration_0003_modified_files": "Please note that the following files were found to be manually modified and might be overwritten at the end of the upgrade : {manually_modified_files}",
     "migration_0005_postgresql_94_not_installed": "Postgresql was not installed on your system. Nothing to do!",
     "migration_0005_postgresql_96_not_installed": "Postgresql 9.4 has been found to be installed, but not postgresql 9.6 !? Something weird might have happened on your system :( ...",
+    "migration_0005_not_enough_space": "Not enough space is available in {path} to run the migration right now :(.",
     "migrations_backward": "Migrating backward.",
     "migrations_bad_value_for_target": "Invalid number for target argument, available migrations numbers are 0 or {}",
     "migrations_cant_reach_migration_file": "Can't access migrations files at path %s",

src/yunohost/data_migrations/0005_postgresql_9p4_to_9p6.py

@@ -5,6 +5,7 @@ from moulinette.core import MoulinetteError
 from moulinette.utils.log import getActionLogger
 
 from yunohost.tools import Migration
+from yunohost.utils.filesystem import free_space_in_directory, space_used_by_directory
 
 logger = getActionLogger('yunohost.migration')
 
@@ -12,7 +13,6 @@ logger = getActionLogger('yunohost.migration')
 class MyMigration(Migration):
     "Migrate DBs from Postgresql 9.4 to 9.6 after migrating to Stretch"
 
-
     def migrate(self):
 
         if not self.package_is_installed("postgresql-9.4"):
@@ -22,8 +22,8 @@ class MyMigration(Migration):
         if not self.package_is_installed("postgresql-9.6"):
             raise MoulinetteError(m18n.n("migration_0005_postgresql_96_not_installed"))
 
-        # FIXME / TODO : maybe add checks about the size of
-        #  /var/lib/postgresql/9.4/main/base/ compared to available space ?
+        if not space_used_by_directory("/var/lib/postgresql/9.4") < free_space_in_directory("/var/lib/postgresql"):
+            raise MoulinetteError(m18n.n("migration_0005_not_enough_space", path="/var/lib/postgresql/"))
 
         subprocess.check_call("service postgresql stop", shell=True)
         subprocess.check_call("pg_dropcluster --stop 9.6 main", shell=True)
@@ -35,7 +35,6 @@ class MyMigration(Migration):
 
         pass
 
-
     def package_is_installed(self, package_name):
 
         p = subprocess.Popen("dpkg --list | grep -q -w {}".format(package_name), shell=True)

src/yunohost/utils/filesystem.py

@@ -23,3 +23,7 @@ import os
 def free_space_in_directory(dirpath):
     stat = os.statvfs(dirpath)
     return stat.f_frsize * stat.f_bavail
+
+def space_used_by_directory(dirpath):
+    stat = os.statvfs(dirpath)
+    return stat.f_frsize * stat.f_blocks