Re: [RFC PATCH v2 15/19] mm/gup: Introduce vaddr_pin_pages()

[Ira Weiny]

On Mon, Aug 12, 2019 at 09:28:14AM -0300, Jason Gunthorpe wrote:
> On Fri, Aug 09, 2019 at 03:58:29PM -0700, ira.weiny@xxxxxxxxx wrote:
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> > 
> > The addition of FOLL_LONGTERM has taken on additional meaning for CMA
> > pages.
> > 
> > In addition subsystems such as RDMA require new information to be passed
> > to the GUP interface to track file owning information.  As such a simple
> > FOLL_LONGTERM flag is no longer sufficient for these users to pin pages.
> > 
> > Introduce a new GUP like call which takes the newly introduced vaddr_pin
> > information.  Failure to pass the vaddr_pin object back to a vaddr_put*
> > call will result in a failure if pins were created on files during the
> > pin operation.
> 
> Is this a 'vaddr' in the traditional sense, ie does it work with
> something returned by valloc?

...or malloc in user space, yes.  I think the idea is that it is a user virtual
address.

> 
> Maybe another name would be better?

Maybe, the name I had was way worse...  So I'm not even going to admit to it...

;-)

So I'm open to suggestions.  Jan gave me this one, so I figured it was safer to
suggest it...

:-D

> 
> I also wish GUP like functions took in a 'void __user *' instead of
> the unsigned long to make this clear :\

Not a bad idea.  But I only see a couple of call sites who actually use a 'void
__user *' to pass into GUP...  :-/

For RDMA the address is _never_ a 'void __user *' AFAICS.

For the new API, it may be tractable to force users to cast to 'void __user *'
but it is not going to provide any type safety.

But it is easy to change in this series.

What do others think?

Ira

> 
> Jason
>