[Qemu-devel] Device initialisation problem:

[Qemu-devel] Device initialisation problem:

[Ian Molton]

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Hi,

I'm trying to use the qption parser to parse my device option string,
which is formatted like this:

- -vrng dev=/dev/foo,rate=10K

and I mostly got things to work by using this, in vl.c:

static int virtio_rng_parse(const char *arg)
{
        QemuOpts *opts;

    if (strcmp(arg, "none") == 0) {
        return 0;
    }
    if (!strncmp(arg, "dev", 3)) {
        /* have params -> parse them */
        opts = qemu_opts_parse(&qemu_device_opts, arg, NULL);
        if (!opts)
            return  -1;
    } else {
        /* create empty opts */
        opts = qemu_opts_create(&qemu_device_opts, NULL, 0);
    }

    qemu_opt_set(opts, "driver", "virtio-rng-pci");

    return 0;
}

However when I tried to create my own opts layout so that I could take
advantage of the OPT_SIZE  option type, I ran into problems.

I defined the following:

QemuOptsList qemu_rng_opts = {
    .name = "virtio-rng-pci",
    .head = QTAILQ_HEAD_INITIALIZER(qemu_rng_opts.head),
    .desc = {
        {
            .name = "dev",
            .type = QEMU_OPT_STRING,
        },
        {
            .name = "rate",
            .type = QEMU_OPT_SIZE,
        },
        { /* end if list */ }
    }
};

And modified the code in vl.c to read:

static int virtio_rng_parse(const char *arg)
{
        QemuOpts *opts;

    if (strcmp(arg, "none") == 0) {
        return 0;
    }
    if (!strncmp(arg, "dev", 3)) {
        /* have params -> parse them */
        opts = qemu_opts_parse(&qemu_rng_opts, arg, NULL);
        if (!opts)
            return  -1;
    } else {
        /* create empty opts */
        opts = qemu_opts_create(&qemu_rng_opts, NULL, 0);
    }

//    qemu_opt_set(opts, "driver", "virtio-rng-pci");

    return 0;
}

But now my driver does not get registered.

So it seems I can use &qemu_device_opts and forego the nice parsing, or
I can get nice parsing and not have a device.

What am I missing here ?

- -Ian
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Re: [Qemu-devel] Device initialisation problem: partially solved.

[Ian Molton]

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Hash: SHA1

Further investigation seems to have highlighted the problem:

My code is correctly decoding the OPT_SIZE parameter into the
'value.uint' field in a QemuOpt

I've also got the devices properties set up, so that the device may
receive its data.

Eg.

in vl.c

static int virtio_rng_parse(const char *arg)
{
        QemuOpts *opts;

    if (strcmp(arg, "none") == 0) {
        return 0;
    }
    if (!strncmp(arg, "dev", 3)) {
        /* have params -> parse them */
        opts = qemu_opts_parse(&qemu_rng_opts, arg, NULL);
        if (!opts)
            return  -1;
    } else {
        /* create empty opts */
        opts = qemu_opts_create(&qemu_rng_opts, NULL, 0);
    }

    qemu_opt_set(opts, "driver", "virtio-rng-pci");

    return 0;
}

and in hw/virtio.c I have:

,{
        .qdev.name = "virtio-rng-pci",
        .qdev.size = sizeof(VirtIOPCIProxy),
        .init      = virtio_rng_init_pci,
        .exit      = virtio_exit_pci,
        .qdev.props = (Property[]) {
            DEFINE_RNG_PROPERTIES(VirtIOPCIProxy, rng),
            DEFINE_PROP_END_OF_LIST(),
        },
        .qdev.reset = virtio_pci_reset,
    }

Where DEFINE_RNG_PROPERTIES is defined as:

#define DEFINE_RNG_PROPERTIES(_state, _conf)                            \
    DEFINE_PROP_STRING("dev",   _state, _conf.device), \
    DEFINE_PROP_UINT32("rate",   _state, _conf.rate, 0)

So as you can see, I was expecting the rate property to be decoded as an
OPT_SIZE type and that value to be fed into conf.rate

This doesn't happen because in hw/qemu.c we have:

qemu_opt_foreach(opts, set_property, qdev, 1)

Which is doing:

QTAILQ_FOREACH(opt, &opts->head, next) {
        rc = func(opt->name, ******opt->str******, opaque);

IOW, its not passing the nicely decoded OPT_SIZE, but the original
string value.

I cant see a 'nice' solution to this right now, the choices being to
either reimplement the OPT_SIZE parser as a property parser, which seems
horribly inefficient, or to create a new property parser that does a
nasty hack on the offset of opt->str in order to access opt->value.uint,
which seems horribly evil.

Am I missing something here? It seems there is some confusion as to
wether the property code should do the parsing or the options code. Or
both - but then we need some way to tell the properties code to use the
pre-parsed data in circumstances like mine.

Either that or I'm too tired and should go to bed...

- -Ian




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