Add `mutate_flag` parameter for `fcntl.fcntl`

Feature or enhancement

Proposal:

fcntl.ioctl has a mutate_flag parameter. When set to True, it will pass the arg buffer to the underlying ioctl syscall directly. This is useful for receiving the result which will be written to the arg buffer.

However, fcntl.fcntl doesn't have this parameter, and it only returns bytes as the modified arg buffer. Users need to parse the bytes using the struct module, even if they have a well-defined structure that already implements the write buffer protocol.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Commencez par les points d’entrée fcntl.fcntl et fcntl.ioctl, en comparant la manière dont ioctl gère mutate_flag avec le comportement actuel de fcntl. Vérifiez les tests fcntl existants et les attentes du buffer protocol ; le travail est terminé lorsque fcntl.fcntl prend en charge le paramètre proposé et que les tests couvrent la réception du buffer modifié sans nécessiter de struct parsing.