Re: [PATCH v2 2/9] dmapool: cleanup error messages

[Douglas Gilbert <dgilbert-qazKcTl6WRFWk0Htik3J/w@public.gmane.org>]

On 2018-08-03 02:38 PM, Andy Shevchenko wrote:
> On Fri, Aug 3, 2018 at 8:03 PM, Tony Battersby <tonyb-vFAe+i1/wJI5UWNf+nJyDw@public.gmane.org> wrote:
>> On 08/03/2018 12:22 PM, Matthew Wilcox wrote:
>>> On Fri, Aug 03, 2018 at 06:59:20PM +0300, Andy Shevchenko wrote:
>>>>>>> I'm pretty sure this was created in an order to avoid bad looking (and
>>>>>>> in some cases frightening) "NULL device *" part.
>>>> JFYI: git log --no-merges --grep 'NULL device \*'
>>> I think those commits actually argue in favour of Tony's patch to remove
>>> the special casing.  Is it really useful to create dma pools with a NULL
>>> device?
> 
>> dma_alloc_coherent() does appear to support a NULL dev, so it might make
>> sense in theory.  But I can't find any in-tree callers that actually
>> pass a NULL dev to dma_pool_create().  So for one of the dreaded (NULL
>> device *) messages to show up, it would take both a new caller that
>> passes a NULL dev to dma_pool_create() and a bug to cause the message to
>> be printed.  Is that worth the special casing?
> 
> So, then you need to rephrase the commit message explaining this
> ("NULL device is wrong to pass in the first place... bla bla bla").
> 

"Pre-condition(s)", you might use that term for non-obvious requirements
for a function. The assumption then is if it/they are violated that
your function won't work. It also implies your function does not check them.
One implicit pre-condition on almost all C functions that take a pointer:
that the pointer points to accessible memory.

Doug Gilbert