Hi Laurent,
Please refer to the comments below.
On 03/22/2012 12:16 PM, Laurent Pinchart wrote:
> Hi Tomasz,
>
> Thanks for the patch.
>
> On Tuesday 13 March 2012 11:17:02 Tomasz Stanislawski wrote:
>> This patch adds extension to V4L2 api. It allow to export a mmap buffer as
>> file descriptor. New ioctl VIDIOC_EXPBUF is added. It takes a buffer offset
>> used by mmap and return a file descriptor on success.
>
> I know code is more fun to write than documentation, but
> Documentation/DocBook/media/v4l will be sad if this patch is merged as-is ;-)
>
Ok. I will prepare the documentation just after there will be consensus
about shape of buffer exporting API :).
>> Signed-off-by: Tomasz Stanislawski <t.stanislaws@xxxxxxxxxxx>
>> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
>> ---
>> drivers/media/video/v4l2-compat-ioctl32.c | 1 +
>> drivers/media/video/v4l2-ioctl.c | 11 +++++++++++
>> include/linux/videodev2.h | 20 ++++++++++++++++++++
>> include/media/v4l2-ioctl.h | 2 ++
>> 4 files changed, 34 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/media/video/v4l2-compat-ioctl32.c
>> b/drivers/media/video/v4l2-compat-ioctl32.c index e6f67aa..fd157cb 100644
>> --- a/drivers/media/video/v4l2-compat-ioctl32.c
>> +++ b/drivers/media/video/v4l2-compat-ioctl32.c
>> @@ -954,6 +954,7 @@ long v4l2_compat_ioctl32(struct file *file, unsigned int
>> cmd, unsigned long arg) case VIDIOC_S_FBUF32:
>> case VIDIOC_OVERLAY32:
>> case VIDIOC_QBUF32:
>> + case VIDIOC_EXPBUF:
>> case VIDIOC_DQBUF32:
>> case VIDIOC_STREAMON32:
>> case VIDIOC_STREAMOFF32:
>> diff --git a/drivers/media/video/v4l2-ioctl.c
>> b/drivers/media/video/v4l2-ioctl.c index 74cab51..a125016 100644
>> --- a/drivers/media/video/v4l2-ioctl.c
>> +++ b/drivers/media/video/v4l2-ioctl.c
>> @@ -207,6 +207,7 @@ static const char *v4l2_ioctls[] = {
>> [_IOC_NR(VIDIOC_S_FBUF)] = "VIDIOC_S_FBUF",
>> [_IOC_NR(VIDIOC_OVERLAY)] = "VIDIOC_OVERLAY",
>> [_IOC_NR(VIDIOC_QBUF)] = "VIDIOC_QBUF",
>> + [_IOC_NR(VIDIOC_EXPBUF)] = "VIDIOC_EXPBUF",
>> [_IOC_NR(VIDIOC_DQBUF)] = "VIDIOC_DQBUF",
>> [_IOC_NR(VIDIOC_STREAMON)] = "VIDIOC_STREAMON",
>> [_IOC_NR(VIDIOC_STREAMOFF)] = "VIDIOC_STREAMOFF",
>> @@ -938,6 +939,16 @@ static long __video_do_ioctl(struct file *file,
>> dbgbuf(cmd, vfd, p);
>> break;
>> }
>> + case VIDIOC_EXPBUF:
>> + {
>> + struct v4l2_exportbuffer *p = arg;
>> +
>> + if (!ops->vidioc_expbuf)
>> + break;
>> +
>> + ret = ops->vidioc_expbuf(file, fh, p);
>
> You can pass arg to ops->vidioc_expbuf() directly, there's no need to create a
> struct v4l2_exportbuffer *p variable.
>
No problem. I tried to follow style of other ioctls.
Notice that adding this temporary variable provides some
form of type checking. I mean using a proper structure for
a proper callback.
>> + break;
>> + }
>> case VIDIOC_DQBUF:
>> {
>> struct v4l2_buffer *p = arg;
>> diff --git a/include/linux/videodev2.h b/include/linux/videodev2.h
>> index bb6844e..e71c787 100644
>> --- a/include/linux/videodev2.h
>> +++ b/include/linux/videodev2.h
>> @@ -680,6 +680,25 @@ struct v4l2_buffer {
>> #define V4L2_BUF_FLAG_NO_CACHE_INVALIDATE 0x0800
>> #define V4L2_BUF_FLAG_NO_CACHE_CLEAN 0x1000
>>
>> +/**
>> + * struct v4l2_exportbuffer - export of video buffer as DMABUF file
>> descriptor
>> + *
>> + * @fd: file descriptor associated with DMABUF (set by driver)
>> + * @mem_offset: for non-multiplanar buffers with memory ==
>> V4L2_MEMORY_MMAP;
>
> I don't think we will ever support exporting anything else than
> V4L2_MEMORY_MMAP buffers. What will happen for multiplanar buffers ?
>
Every plane is described by its separate mem-offset. So planes are
exported as separate DMABUF. I will update field description.
>> + * offset from the start of the device memory for this plane,
>> + * (or a "cookie" that should be passed to mmap() as offset)
>> + *
>
> Shouldn't the mem_offset field always be set to the mmap cookie value ? I'm a
> bit confused by the "or" part, it seems to have been copied from the
> v4l2_buffer documentation directly. We should clarify that.
>
Ok. I agree.
>> + * Contains data used for exporting a video buffer as DMABUF file
>> + * descriptor. Uses the same 'cookie' as mmap() syscall. All reserved
>> fields
>> + * must be set to zero.
>> + */
>> +struct v4l2_exportbuffer {
>> + __u32 fd;
>> + __u32 reserved0;
>
> Why is there a reserved field here ?
>
I expected that struct v4l2_requestbuffer might allow exporting buffers described
by something else than 'mmap cookie'. Union could be used for different schemes i.e.
struct v4l2_exportbuffer {
__u32 fd;
__u32 type;
union {
__u32 mem_offset;
__u32 reserved[14];
/* other descriptions */
} m;
};
Adding reserved0 field will allow to introduce field type, and keep the union at
64-bit aligned address to keep compatibility between 32/64bit libraries.
Field type == 0 would indicate description of a buffer using 'mmap offset'.
>> + __u32 mem_offset;
>> + __u32 reserved[13];
>> +};
>> +
>> /*
>> * O V E R L A Y P R E V I E W
>> */
>> @@ -2303,6 +2322,7 @@ struct v4l2_create_buffers {
>> #define VIDIOC_S_FBUF _IOW('V', 11, struct v4l2_framebuffer)
>> #define VIDIOC_OVERLAY _IOW('V', 14, int)
>> #define VIDIOC_QBUF _IOWR('V', 15, struct v4l2_buffer)
>> +#define VIDIOC_EXPBUF _IOWR('V', 16, struct v4l2_exportbuffer)
>> #define VIDIOC_DQBUF _IOWR('V', 17, struct v4l2_buffer)
>> #define VIDIOC_STREAMON _IOW('V', 18, int)
>> #define VIDIOC_STREAMOFF _IOW('V', 19, int)
>> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
>> index 4df031a..d8716c6f 100644
>> --- a/include/media/v4l2-ioctl.h
>> +++ b/include/media/v4l2-ioctl.h
>> @@ -120,6 +120,8 @@ struct v4l2_ioctl_ops {
>> int (*vidioc_reqbufs) (struct file *file, void *fh, struct
>> v4l2_requestbuffers *b); int (*vidioc_querybuf)(struct file *file, void
>> *fh, struct v4l2_buffer *b); int (*vidioc_qbuf) (struct file *file, void
>> *fh, struct v4l2_buffer *b);
>> + int (*vidioc_expbuf) (struct file *file, void *fh,
>> + struct v4l2_exportbuffer *e);
>> int (*vidioc_dqbuf) (struct file *file, void *fh, struct v4l2_buffer
>> *b);
>>
>> int (*vidioc_create_bufs)(struct file *file, void *fh, struct
>> v4l2_create_buffers *b);
>
Regards,
Tomasz Stanislawski
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