linux-kernel - Re: [PATCH v3 06/11] staging/android: turn fence_info into a _

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Message-ID: <56B2111A.8080103@linux.intel.com>
Date:	Wed, 3 Feb 2016 15:39:22 +0100
From:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:	Gustavo Padovan <gustavo@...ovan.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	dri-devel@...ts.freedesktop.org,
	Daniel Stone <daniels@...labora.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
Subject: Re: [PATCH v3 06/11] staging/android: turn fence_info into a __u64
 pointer

Op 03-02-16 om 14:25 schreef Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
>
> Turn sync_fence_info into __u64 type enable us to extend the struct in the
> future without breaking the ABI.
>
> v2: use type __u64 for fence_info
>
> v3: fix commit message to reflect the v2 change
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.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 2ab0c20..8425457 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 a0cf357..e649953 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	sync_fence_info[0];
> +	__u64	sync_fence_info;
>  };
>  
>  #define SYNC_IOC_MAGIC		'>'
This still doesn't do what you expect it to.

I think this is what you want is for userspace to do:

struct sync_file_info info;

info.flags = info.num_fences = 0;
ioctl(fd, SYNC_IOC_FENCE_INFO, &info);
if (info.num_fences) {
info.sync_fence_info = (uintptr)kcalloc(info.num_fences, sizeof(struct sync_fence_info));
ioctl(fd, SYNC_IOC_FENCE_INFO, &info);
}

Maybe userspace could preallocate the max in advance and set num_fences higher,

kernel would do something like:

num_fences = min(info.num_fences, sync->num_fences);
struct sync_fence_info array[num_fences];

info.num_fences = sync->num_fences;
if (num_fences &&
    copy_to_user((void * __user)(unsigned long)info.sync_fence_info, array, num_fences  * sizeof(array)))
 return -EFAULT;