On Wed, Feb 03, 2016 at 03:39:22PM +0100, Maarten Lankhorst wrote:
> Op 03-02-16 om 14:25 schreef Gustavo Padovan:
> > From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx>
> > ---
> > 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);
s/kcalloc/calloc/ since this is userspace, i.e. yes I agree. In general if
you have a variable sized array for your ioctl what you need to do in the
kernel:
- compute how many you need.
- if userspace array was too small, fail with -EINVAL
- but _always_ update the array size to what would be needed.
Then the loop above which Maarten laid out will work nicely. Of course
since it's a separate array then you also need separate copy_to_user calls
(I didn't check whether that would work as-is).
-Daniel
> }
>
> 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;
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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