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

Maarten Lankhorst
2016-02-01T08:41:44Z

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.
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.