[Qemu-devel] Adding -dtb option to qemu

[Grant Likely]

Hey Peter,

I need some advice.  I'm adding a -dtb option to qemu for specifying a
dtb filename to be passed on to the kernel, similar to how the -initrd
flag works.  The dtb filename needs to then be passed on to the
selected machine, and it looks like the machine->init() callback is
the best way to do that.

However, the current init callback prototype looks like this:

typedef void QEMUMachineInitFunc(ram_addr_t ram_size,
                                 const char *boot_device,
                                 const char *kernel_filename,
                                 const char *kernel_cmdline,
                                 const char *initrd_filename,
                                 const char *cpu_model);

Now, I could simply add an new "dtb_filename" to the argument list and
fix up all of the users (looks to be about 90 machines), but that
seems like a lot of churn that will need to be repeated the next time
a new argument needs to be passed to the init func.

Alternately, I could do something like this:

struct machine_args {
        ram_addr_t ram_size;
        const char *boot_device;
        const char *kernel_filename,
        const char *kernel_cmdline,
        const char *initrd_filename,
        const char *dtb_filename,
        const char *cpu_model,
};

typedef void QEMUMachineInitFunc(const struct machine_args *args);

And then I'd fix up all the users, which would be about the same
amount of churn, but subsequent additions would be a lot easier.

A third option would be to add a new ".dt_init()" that is executed
instead of .init() if populated, but that seems like an ugly band-aid
to me.

How should I approach this?  Or is there a better way to pass data to
so that it is available at machine->init() time?

g.