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    SubjectWhy does ionice(1) ban the user to set back to 'none' class?
    Hi Jens,

    I meet a problem when I use ionice(1) to adjust a process's io priority.
    I do the following operations:

    $ ionice -p${pid}
    none: prio 0
    $ ionice -p${pid} -c2 -n4
    $ ionice -p${pid}
    best-effort: prio 4
    $ ionice -p${pid} -c0 -n0
    $ ionice -p${pid}
    best-effort: prio 0

    So I cannot set scheduling class back to 'none'. If I call ioprio_set(2)
    directly, it will be fine. But if I use ionice(1), I cannot change it. I
    read the docs about ionice in [1]. I notice this code:

    switch (ioprio_class) {
    case IOPRIO_CLASS_NONE:
    ioprio_class = IOPRIO_CLASS_BE;
    ^^^^^^^^^^^^^^^^
    *It means that we cannot set back to none.*
    break;
    case IOPRIO_CLASS_RT:
    case IOPRIO_CLASS_BE:
    break;
    case IOPRIO_CLASS_IDLE:
    ioprio = 7;
    break;
    default:
    printf("bad prio class %d\n", ioprio_class);
    return 1;
    }

    My question is why we need to ban the user to set back to 'none'. Is there
    some reasons? Thank you.

    [Sorry, I don't subscribe linux-doc and linux-kernel mailing list.
    Please CC to me.]

    1. ${linux_src}/Documentation/block/ioprio.txt.

    Regards,
    Zheng


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