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

[Felipe Ferreri Tonello <eu@felipetonello.com>]

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Hi Michael,

On 09/01/16 03:47, Michal Nazarewicz wrote:
> Reduce number of allocations, simplify memory management and reduce
> memory usage by stacking the gmidi_in_port elements at the end of the
> f_midi structure using a flexible array.
> 
> Also, observe that gmidi_in_port::midi pointer is *never* used for any
> purpose so it can be safely removed.
> 
> Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
> ---
>  drivers/usb/gadget/function/f_midi.c | 43 ++++++++++++------------------------
>  1 file changed, 14 insertions(+), 29 deletions(-)
> 
> On Tue, Jan 05 2016, Dan Carpenter wrote:
>> On Tue, Jan 05, 2016 at 02:55:31PM +0100, Michal Nazarewicz wrote:
>>> @@ -568,12 +568,12 @@ static int f_midi_in_open(struct snd_rawmidi_substream *substream)
>>>  {
>>>  	struct f_midi *midi = substream->rmidi->private_data;
>>>  
>>> -	if (!midi->in_port[substream->number])
>>> +	if (substream->number > midi->in_ports)
>>
>> This is off by one.  It should be >= midi->in_ports.
> 
> Fixed.
> 
> Since there were no objections to this small patch set (i.e. there was
> mostly silence about it), I’ll go ahead and interpret it as ‘go ahead
> and properly submit it’. :)
> 
> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
> index 898a570..fd67af2 100644
> --- a/drivers/usb/gadget/function/f_midi.c
> +++ b/drivers/usb/gadget/function/f_midi.c
> @@ -55,7 +55,6 @@ static const char f_midi_longname[] = "MIDI Gadget";
>   * USB <- IN endpoint  <- rawmidi
>   */
>  struct gmidi_in_port {
> -	struct f_midi *midi;

This change is unrelated. I sent a patch removing this pointer as well.

>  	int active;
>  	uint8_t cable;
>  	uint8_t state;
> @@ -78,7 +77,6 @@ struct f_midi {
>  
>  	struct snd_rawmidi_substream *in_substream[MAX_PORTS];
>  	struct snd_rawmidi_substream *out_substream[MAX_PORTS];
> -	struct gmidi_in_port	*in_port[MAX_PORTS];
>  
>  	unsigned long		out_triggered;
>  	struct tasklet_struct	tasklet;
> @@ -87,6 +85,8 @@ struct f_midi {
>  	int index;
>  	char *id;
>  	unsigned int buflen, qlen;
> +
> +	struct gmidi_in_port	in_ports_array[/* in_ports */];
>  };
>  
>  static inline struct f_midi *func_to_midi(struct usb_function *f)
> @@ -529,11 +529,11 @@ static void f_midi_transmit(struct f_midi *midi, struct usb_request *req)
>  	req->length = 0;
>  	req->complete = f_midi_complete;
>  
> -	for (i = 0; i < MAX_PORTS; i++) {
> -		struct gmidi_in_port *port = midi->in_port[i];
> +	for (i = 0; i < midi->in_ports; i++) {
> +		struct gmidi_in_port *port = midi->in_ports_array + i;
>  		struct snd_rawmidi_substream *substream = midi->in_substream[i];
>  
> -		if (!port || !port->active || !substream)
> +		if (!port->active || !substream)
>  			continue;
>  
>  		while (req->length + 3 < midi->buflen) {
> @@ -568,12 +568,12 @@ static int f_midi_in_open(struct snd_rawmidi_substream *substream)
>  {
>  	struct f_midi *midi = substream->rmidi->private_data;
>  
> -	if (!midi->in_port[substream->number])
> +	if (substream->number >= midi->in_ports)
>  		return -EINVAL;
>  
>  	VDBG(midi, "%s()\n", __func__);
>  	midi->in_substream[substream->number] = substream;
> -	midi->in_port[substream->number]->state = STATE_UNKNOWN;
> +	midi->in_ports_array[substream->number].state = STATE_UNKNOWN;
>  	return 0;
>  }
>  
> @@ -589,11 +589,11 @@ static void f_midi_in_trigger(struct snd_rawmidi_substream *substream, int up)
>  {
>  	struct f_midi *midi = substream->rmidi->private_data;
>  
> -	if (!midi->in_port[substream->number])
> +	if (substream->number >= midi->in_ports)
>  		return;
>  
>  	VDBG(midi, "%s() %d\n", __func__, up);
> -	midi->in_port[substream->number]->active = up;
> +	midi->in_ports_array[substream->number].active = up;
>  	if (up)
>  		tasklet_hi_schedule(&midi->tasklet);
>  }
> @@ -1067,14 +1067,11 @@ static void f_midi_free(struct usb_function *f)
>  {
>  	struct f_midi *midi;
>  	struct f_midi_opts *opts;
> -	int i;
>  
>  	midi = func_to_midi(f);
>  	opts = container_of(f->fi, struct f_midi_opts, func_inst);
>  	kfree(midi->id);
>  	mutex_lock(&opts->lock);
> -	for (i = opts->in_ports - 1; i >= 0; --i)
> -		kfree(midi->in_port[i]);
>  	kfree(midi);
>  	--opts->refcnt;
>  	mutex_unlock(&opts->lock);
> @@ -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?

>  	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);
> @@ -1161,8 +1148,6 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>  	return &midi->func;
>  
>  setup_fail:
> -	for (--i; i >= 0; i--)
> -		kfree(midi->in_port[i]);
>  	kfree(midi);
>  	return ERR_PTR(status);
>  }
> 

Felipe

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