Re: [PATCH 06/10] staging/android: turn fence_info into a __64 pointer

[Gustavo Padovan <gustavo@padovan.org>]

Hi Maarten,

2016-02-01 Maarten Lankhorst <maarten.lankhorst@linux.intel.com>:

> Op 29-01-16 om 22:20 schreef Gustavo Padovan:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> >
> > Making fence_info a pointer enables us to extend the struct in the future
> > without breaking the ABI.
> >
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > ---
> >  drivers/staging/android/sync.c      | 2 +-
> >  drivers/staging/android/uapi/sync.h | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> > index f7530f0..51d4f47 100644
> > --- a/drivers/staging/android/sync.c
> > +++ b/drivers/staging/android/sync.c
> > @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> >  	if (info->status >= 0)
> >  		info->status = !info->status;
> >  
> > -	len = sizeof(struct sync_file_info);
> > +	len = sizeof(struct sync_file_info) - sizeof(__u64 *);
> >  
> >  	for (i = 0; i < sync_file->num_fences; ++i) {
> >  		struct fence *fence = sync_file->cbs[i].fence;
> > diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> > index ed281fc..9f07aa7 100644
> > --- a/drivers/staging/android/uapi/sync.h
> > +++ b/drivers/staging/android/uapi/sync.h
> > @@ -54,7 +54,7 @@ struct sync_file_info {
> >  	char	name[32];
> >  	__s32	status;
> >  
> > -	__u8	fence_info[0];
> > +	__u64	*fence_info;
> >  };
> >
> Pointers are awful, it should be a __u64 since it's a pointer type. Userspace should cast it to a uintptr_t in userspace.

Oh, I made a mistake. I'll fix this.


> This structure also won't work on 64-bits systems, there may be a hole between fence_info and status (or num_fences in next patch).
> 
> It's probably best to move it to the top and ensure the struct is 64-bits aligned.

That is not possible because we are not allocating only 64bits there but
a array of struct fence_info, so it needs to be the last one. Maybe we
can add some sort of padding?


	Gustavo