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

Gustavo Padovan
2016-02-01T18:00:20Z

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