linux-kernel - Re: [PATCHv2 1/2] usb: gadget: f_midi: use flexible array member for gmidi_in

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Message-ID: <xa1tbn8iq3je.fsf@mina86.com>
Date:	Mon, 18 Jan 2016 17:02:29 +0100
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Felipe Ferreri Tonello <eu@...ipetonello.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Robert Baldyga <r.baldyga@...sung.com>,
	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	Pawel Szewczyk <p.szewczyk@...sung.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/2] usb: gadget: f_midi: use flexible array member for gmidi_in_port elements

> 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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.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  ミハウ “mina86” ナザレヴイツ  (o o)
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