MDEV-26231:mysql_upgrade attempts to remove plugins which it failed to install

[an3l]

When allocating array for installed MYSQL_JSON plugin, size is set.
When uninstalling the plugin, check string instead of size.

Basing the PR against the correct MariaDB version

• This is a new feature and the PR is based against the latest MariaDB development branch.
• [ x] This is a bug fix and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• [ x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [x ] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.

[cvicentiu]

Hi @an3l!

I don't understand what this patch changes.

ds_plugin_data_types only has its length member != 0 if installing a plugin succeded.

First initialization of the dynamic string is here:

int main(int argc, char **argv)
{
[...]

  if (init_dynamic_string(&ds_args, "", 512, 256) ||
      init_dynamic_string(&conn_args, "", 512, 256) ||
      init_dynamic_string(&ds_plugin_data_types, "", 512, 256))
    die("Out of memory");

This sets the length of the string to 0, but it pre-allocates. Fine.

Then the only place that changes the ds_plugin_data_types string is:

        if(!run_query("INSTALL SONAME 'type_mysql_json'", NULL, TRUE))
        {
          dynstr_append(&ds_plugin_data_types, "'type_mysql_json'");
          dynstr_append(&ds_plugin_data_types, "\n");
          break;
        }

So my question then is:

Does run_query return success even if the executed query threw an error? In that case, the bug should be fixed there, because the length checking of ds_plugin_data_types seems fine to me.

[an3l]

HI @cvicentiu , yes I have updated now to catch error for query plugin and properly skip uninstall phase if there is no plugin installed at all.
Results:

• Simulate wrong query:

if(!run_query("INSTALL SONAME 'type_mysql_json1'", &ds_result, TRUE))

Check clients

# No plugin installed
MariaDB [test]> show create table t;
ERROR 4161 (HY000): Unknown data type: 'MYSQL_JSON'

# mariadb_upgrade
$ sudo ./client/mysql_upgrade -uroot -S /tmp/mysql.sock --force
Phase 2/7: Installing used storage engines... Skipped
installing plugin for MYSQL_JSON data type
Failed to install the plugin 'type_mysql_json' for MYSQL_JSON data type
FATAL ERROR: Upgrade failed