Support for running MariaDB with a read-only data directory

Description
I would like to run MariaDB against a read-only data directory for archival purposes. The use case is accessing an old database (multiple TBs) on an archive drive that is mounted read-only by default. Copying this data is impractical, but occasional queries are still needed.

Currently this is not possible, because MariaDB expects to create/write certain files inside the datadir during startup.

Example failure:

[ERROR] mariadbd: Can't create/write to file './ddl_recovery.log' (Errcode: 30 "Read-only file system")

[ERROR] DDL_LOG: Failed to create ddl log file: ./ddl_recovery.log

[ERROR] Aborting

Feature Request
Add configuration options to relocate or disable files that must otherwise be created in the datadir (e.g. `ddl_recovery.log`, `*.lower-test`, etc.). This would allow MariaDB to start successfully with a read-only datadir, provided all logging and temporary files are redirected elsewhere.

Minimal Repro (Docker Compose)

services:

  mariadb:

    image: mariadb:latest

    container_name: old_mariadb

    volumes:

      - ./data:/mnt/data:ro   # read-only dataset

    ports:

      - "3306:3306"

    entrypoint: ["mariadbd"]   # bypass entrypoint to skip chown

    command: >

      --datadir=/mnt/data

      --basedir=/usr

      --read-only=ON

      --skip-log-bin

      --tmpdir=/var/tmp

Why this matters
Enabling MariaDB to run on a read-only datadir would support:

• Querying archive databases without risk of modification.
• Running MariaDB directly on cold-storage volumes.
• Safer "forensic" or "historic" analysis use cases.

Even with `--read-only=ON` and external `tmpdir/log` paths, the server still expects to write into the datadir, which prevents this use case today.

see also github

If this is already possible and I have missed something, help getting around this issues would be highly appreciated!