linux-kernel - Re: [PATCH] usbnet: ax88179_178a: Add support for writing the EEPROM

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Date:   Thu, 25 Aug 2016 12:07:33 +0200
From:   Alban Bedel <alban.bedel@...onic-design.de>
To:     Oliver Neukum <oneukum@...e.com>
Cc:     Alban Bedel <alban.bedel@...onic-design.de>,
        Freddy Xin <freddy@...x.com.tw>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] usbnet: ax88179_178a: Add support for writing the
 EEPROM

On Thu, 25 Aug 2016 11:16:36 +0200
Oliver Neukum <oneukum@...e.com> wrote:

> On Wed, 2016-08-24 at 16:40 +0200, Alban Bedel wrote:
> > On Wed, 24 Aug 2016 16:30:39 +0200
> > Oliver Neukum <oneukum@...e.com> wrote:
> >   
> > > On Wed, 2016-08-24 at 15:52 +0200, Alban Bedel wrote:  
> 
> > > > +       if (block != data)
> > > > +               kfree(block);    
> > > 
> > > And if block == dta, what frees the memory?  
> > 
> > In this case this function didn't allocate any memory, so there is
> > nothing to free.  
> 
> Hi,
> 
> I see. kfree() has a check for NULL, so you could drop the
> test, but it doesn't matter much either way.

I think you misunderstand something here. data is the buffer passed
by the caller and block is a local variable. There is two cases:

1) The data to write is block aligned, then we use the caller buffer
   as is and set block = data.
2) The requested data is not block aligned, then we kalloc block.

In both case the writing loop then use the block pointer. Afterwards
we only need to kfree block in case 2, that is when block != data.

Alban

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