[FFmpeg-devel] [PATCH 1/4] libavutil/opencl: add opencl device list APIs 20130409

[Michael Niedermayer]

On Tue, Apr 09, 2013 at 09:23:51PM +0800, Wei Gao wrote:
> 2013/4/9 Michael Niedermayer <michaelni at gmx.at>
> 
> > On Tue, Apr 09, 2013 at 04:11:27PM +0800, Wei Gao wrote:
> > >
> >
> > >  opencl.c |  298
> > +++++++++++++++++++++++++++++++++------------------------------
> > >  opencl.h |   44 +++++++++
> > >  2 files changed, 201 insertions(+), 141 deletions(-)
> > > b4e23897af2cfec8516fd15e8c32c3d494a22e4c
> >  0001-add-opencl-device-list-APIs-20130409.patch
> > > From 91f88ac410031e01ad9e79c7430012ec78b286cc Mon Sep 17 00:00:00 2001
> > > From: highgod0401 <highgod0401 at gmail.com>
> > > Date: Tue, 9 Apr 2013 14:58:35 +0800
> > > Subject: [PATCH 1/4] add opencl device list APIs 20130409
> > [...]
> >
> > > diff --git a/libavutil/opencl.h b/libavutil/opencl.h
> > > index 6ebde10..1ae65bc 100644
> > > --- a/libavutil/opencl.h
> > > +++ b/libavutil/opencl.h
> > > @@ -39,6 +39,32 @@
> > >
> > >  #define AV_OPENCL_MAX_KERNEL_NAME_SIZE 150
> > >
> > > +#define AV_OPENCL_MAX_PLATFORM_NUM 200
> > > +
> > > +#define AV_OPENCL_MAX_DEVICE_NUM 200
> > > +
> > > +#define AV_OPENCL_MAX_DEVICE_NAME_SIZE 100
> > > +
> > > +#define AV_OPENCL_MAX_PLATFORM_NAME_SIZE 100
> > > +
> >
> > > +typedef struct {
> > > +    int device_type;
> > > +    char device_name[AV_OPENCL_MAX_DEVICE_NAME_SIZE];
> > > +    cl_device_id device_id;
> > > +} AVOpenCLDeviceNode;
> > > +
> > > +typedef struct {
> > > +    cl_platform_id platform_id;
> > > +    char platform_name[AV_OPENCL_MAX_PLATFORM_NAME_SIZE];
> > > +    int device_num;
> > > +    AVOpenCLDeviceNode device_node[AV_OPENCL_MAX_DEVICE_NUM];
> > > +} AVOpenCLPlatformNode;
> > > +
> > > +typedef struct {
> > > +    int platform_num;
> > > +    AVOpenCLPlatformNode platform_node[AV_OPENCL_MAX_PLATFORM_NUM];
> > > +} AVOpenCLDeviceList;
> >
> > If you use an array of structures like device_node and platform_node
> > as part of the public API then the AVOpenCLPlatformNode and
> > AVOpenCLDeviceNode structures cannot be extended later with more
> > fields as this would break old code that has not been recompiled.
> >
> > So depending on if you see the need to ever extend these structures
> > a different layout might make sense.
> > One possibility is an array of pointers to structs as there the array
> > elements dont change size when the struct is extended.
> >
> Thanks, michaelni, do you mean I should define as follows?
> 
> typedef struct {
>     cl_platform_id platform_id;
>     char platform_name[AV_OPENCL_MAX_PLATFORM_NAME_SIZE];
>     int device_num;
>     AVOpenCLDeviceNode *device_node;
> } AVOpenCLPlatformNode;
> 
> typedef struct {
>     int platform_num;
>    AVOpenCLPlatformNode *platform_node;
> } AVOpenCLDeviceList;

Thats not enough to avoid the problem on its own.
For a similar example see streams or programs in AVFormatContext


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is what and why we do it that matters, not just one of them.
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