Re: [PATCHv2 1/2] usb: gadget: f_midi: use flexible array member for gmidi_in_port elements

From: Michal Nazarewicz
Date: Mon Jan 18 2016 - 11:02:39 EST


> On 09/01/16 03:47, Michal Nazarewicz wrote:
>> @@ -55,7 +55,6 @@ static const char f_midi_longname[] = "MIDI Gadget";
>> * USB <- IN endpoint <- rawmidi
>> */
>> struct gmidi_in_port {
>> - struct f_midi *midi;

On Wed, Jan 13 2016, Felipe Ferreri Tonello wrote:
> This change is unrelated. I sent a patch removing this pointer as well.

Has it been merged yet? Which branch? Could you point me to the patch?

>> int active;
>> uint8_t cable;
>> uint8_t state;
>> @@ -1115,26 +1112,16 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>> }
>>
>> /* allocate and initialize one new instance */
>> - midi = kzalloc(sizeof(*midi), GFP_KERNEL);
>> + midi = kzalloc(
>> + sizeof(*midi) + opts->in_ports * sizeof(*midi->in_ports_array),
>> + GFP_KERNEL);
>
> Is there a garantee that the compiler will always use in_ports_array at
> the end of the allocated block?

Yep, see <https://en.wikipedia.org/wiki/Flexible_array_member>.

>
>> if (!midi) {
>> mutex_unlock(&opts->lock);
>> return ERR_PTR(-ENOMEM);
>> }
>>
>> - for (i = 0; i < opts->in_ports; i++) {
>> - struct gmidi_in_port *port = kzalloc(sizeof(*port), GFP_KERNEL);
>> -
>> - if (!port) {
>> - status = -ENOMEM;
>> - mutex_unlock(&opts->lock);
>> - goto setup_fail;
>> - }
>> -
>> - port->midi = midi;
>> - port->active = 0;
>> - port->cable = i;
>> - midi->in_port[i] = port;
>> - }
>> + for (i = 0; i < opts->in_ports; i++)
>> + midi->in_ports_array[i].cable = i;
>>
>> /* set up ALSA midi devices */
>> midi->id = kstrdup(opts->id, GFP_KERNEL);

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