Re: [PATCH v3] staging: vt6656: returns error code on vnt_int_start_interrupt fail

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, May 17, 2019 at 01:15:43PM +0000, Quentin Deslandes wrote:
> On Fri, May 17, 2019 at 11:17:23AM +0200, Greg Kroah-Hartman wrote:
> > On Fri, May 17, 2019 at 07:53:49AM +0000, Quentin Deslandes wrote:
> > > Returns error code from 'vnt_int_start_interrupt()' so the device's private
> > > buffers will be correctly freed and 'struct ieee80211_hw' start function
> > > will return an error code.
> > > 
> > > Signed-off-by: Quentin Deslandes <quentin.deslandes@itdev.co.uk>
> > > ---
> > > v2: returns 'status' value to caller instead of removing it.
> > > v3: add patch version details. Thanks to Greg K-H for his help.
> > 
> > Looking better!
> > 
> > But a few minor things below:
> > 
> > > 
> > >  drivers/staging/vt6656/int.c      |  4 +++-
> > >  drivers/staging/vt6656/int.h      |  2 +-
> > >  drivers/staging/vt6656/main_usb.c | 12 +++++++++---
> > >  3 files changed, 13 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/staging/vt6656/int.c b/drivers/staging/vt6656/int.c
> > > index 504424b19fcf..f3ee2198e1b3 100644
> > > --- a/drivers/staging/vt6656/int.c
> > > +++ b/drivers/staging/vt6656/int.c
> > > @@ -39,7 +39,7 @@ static const u8 fallback_rate1[5][5] = {
> > >  	{RATE_54M, RATE_54M, RATE_36M, RATE_18M, RATE_18M}
> > >  };
> > >  
> > > -void vnt_int_start_interrupt(struct vnt_private *priv)
> > > +int vnt_int_start_interrupt(struct vnt_private *priv)
> > >  {
> > >  	unsigned long flags;
> > >  	int status;
> > > @@ -51,6 +51,8 @@ void vnt_int_start_interrupt(struct vnt_private *priv)
> > >  	status = vnt_start_interrupt_urb(priv);
> > >  
> > >  	spin_unlock_irqrestore(&priv->lock, flags);
> > > +
> > > +	return status;
> > >  }
> > >  
> > >  static int vnt_int_report_rate(struct vnt_private *priv, u8 pkt_no, u8 tsr)
> > > diff --git a/drivers/staging/vt6656/int.h b/drivers/staging/vt6656/int.h
> > > index 987c454e99e9..8a6d60569ceb 100644
> > > --- a/drivers/staging/vt6656/int.h
> > > +++ b/drivers/staging/vt6656/int.h
> > > @@ -41,7 +41,7 @@ struct vnt_interrupt_data {
> > >  	u8 sw[2];
> > >  } __packed;
> > >  
> > > -void vnt_int_start_interrupt(struct vnt_private *priv);
> > > +int vnt_int_start_interrupt(struct vnt_private *priv);
> > >  void vnt_int_process_data(struct vnt_private *priv);
> > >  
> > >  #endif /* __INT_H__ */
> > > diff --git a/drivers/staging/vt6656/main_usb.c b/drivers/staging/vt6656/main_usb.c
> > > index ccafcc2c87ac..71e10b9ae253 100644
> > > --- a/drivers/staging/vt6656/main_usb.c
> > > +++ b/drivers/staging/vt6656/main_usb.c
> > > @@ -483,6 +483,7 @@ static void vnt_tx_80211(struct ieee80211_hw *hw,
> > >  
> > >  static int vnt_start(struct ieee80211_hw *hw)
> > >  {
> > > +	int err = 0;
> > >  	struct vnt_private *priv = hw->priv;
> > >  
> > >  	priv->rx_buf_sz = MAX_TOTAL_SIZE_WITH_ALL_HEADERS;
> > > @@ -496,15 +497,20 @@ static int vnt_start(struct ieee80211_hw *hw)
> > >  
> > >  	if (vnt_init_registers(priv) == false) {
> > >  		dev_dbg(&priv->usb->dev, " init register fail\n");
> > > +		err = -ENOMEM;
> > 
> > Why ENOMEM?  vnt_init_registers() should return a proper error code,
> > based on what went wrong, not true/false.  So fix that up first, and
> > then you can do this patch.
> > 
> > See, your one tiny coding style fix is turning into real cleanups, nice!
> > 
> > >  		goto free_all;
> > >  	}
> > >  
> > > -	if (vnt_key_init_table(priv))
> > > +	if (vnt_key_init_table(priv)) {
> > > +		err = -ENOMEM;
> > 
> > Same here, vnt_key_init_table() should return a real error value, and
> > then just return that here.
> > 
> > >  		goto free_all;
> > > +	}
> > >  
> > >  	priv->int_interval = 1;  /* bInterval is set to 1 */
> > >  
> > > -	vnt_int_start_interrupt(priv);
> > > +	err = vnt_int_start_interrupt(priv);
> > > +	if (err)
> > > +		goto free_all;
> > 
> > Like this, that is the correct thing.
> > 
> > So, this is now going to be a patch series, fixing up those two
> > functions (and any functions they call possibly), and then this can be
> > the last patch of the series.
> > 
> > thanks,
> > 
> > greg k-h
> 
> Thank you for your help, this is getting really exciting! However, I had
> a look at these function (vnt_init_registers() and vnt_key_init_table())
> and some questions popped in my mind.
> 
> If I understand correctly, your request is to fix these function so they
> can return an error code instead of just failing, as I did with
> vnt_int_start_interrupt() in the third patch, which is also the most
> logical behaviour.

Yes, that is correct.

> So, vnt_init_registers() is a big function (~240 lines), which should
> return a proper error code. For this, all the function called in
> vnt_init_registers() should also return a proper error code, right?

Correct.

> What about functions called that does not return any value, but their only
> action is to call a function that return a status code? As I learn with this
> patch, discarding error values is not a acceptable behaviour. Why would we write
> functions returning an error code solely to discard it? So such function should
> be changed too?

Yes, those functions need to be changed too.

> I listed up to 22 function that need to be updated in order to correctly
> propagate errors up to vnt_start() so it could "nicely" fail and here is
> the last problem: regarding this fair amount of changes, how to ensure
> the device will work as well as before? I don't have this device at home
> or at work and it doesn't seems easy to find.

Start small, at the "root" of the call chain, and work backwards.  You
aren't changing any logic, only passing the errors, if there are any,
back on up.

Now if the driver was relying on those functions to fail, that's a bug
in the driver, and someone who has the hardware will notice and send us
an email saying that the patches broke something.  But that's a few
months out, don't worry about that now :)

thanks,

greg k-h