dmabuf in pipeline

[prg.amc]

Hi, currently I have a problem in passing dmabuf fd to other elements.

so, I have plugin which acts as src and it will receive dma fd from another
process using DBUS, so there a way to pass the same fd to next elements, the
next element knows how to access the memory location using the fd.

     GstBuffer *buffer = gst_buffer_new();

    GstAllocator *allocator = gst_dmabuf_allocator_new();

    if (buffer != nullptr && allocator != nullptr) {
      GstMemory *mem = gst_dmabuf_allocator_alloc(allocator, fd, nBufSize);

       gst_buffer_append_memory(buffer, mem);

      *buf = buffer;

This is what i`m using now, but with the above code gstreamer is trying to
copy the data using fdmemory. where the fd is not accessable directly.

*0x5575c30f70 ERROR               fdmemory gstfdmemory.c:126:gst_fd_mem_map:
0x5575e47520: fd 14: mmap failed: No such device
ERROR               fdmemory gstfdmemory.c:126:gst_fd_mem_map: 0x5575e47520:
fd 14: mmap failed: No such device
*

I`m i doing it correct? and i dont have any custom bufferpool manager.






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[Nicolas Dufresne-5]

Le jeudi 08 avril 2021 à 08:53 -0500, prg.amc a écrit :

> Hi, currently I have a problem in passing dmabuf fd to other elements.
>
> so, I have plugin which acts as src and it will receive dma fd from another
> process using DBUS, so there a way to pass the same fd to next elements, the
> next element knows how to access the memory location using the fd.
>
>      GstBuffer *buffer = gst_buffer_new();
>
>     GstAllocator *allocator = gst_dmabuf_allocator_new();
>
>     if (buffer != nullptr && allocator != nullptr) {

These two _new() function will never fail.

>       GstMemory *mem = gst_dmabuf_allocator_alloc(allocator, fd, nBufSize);
>
>        gst_buffer_append_memory(buffer, mem);
>
>       *buf = buffer;
>
> This is what i`m using now, but with the above code gstreamer is trying to
> copy the data using fdmemory. where the fd is not accessable directly.
>
> *0x5575c30f70 ERROR               fdmemory gstfdmemory.c:126:gst_fd_mem_map:
> 0x5575e47520: fd 14: mmap failed: No such device
> ERROR               fdmemory gstfdmemory.c:126:gst_fd_mem_map: 0x5575e47520:
> fd 14: mmap failed: No such device
> *
>
> I`m i doing it correct? and i dont have any custom bufferpool manager.

Along the way, something in your pipeline (undocumented here) is doing a memory
map to access the data. But this mapping failed because the DMABuf FD is
invalid. I would recommend reviewing how you "pass" the FD through DBus, as it
seems this isn't appropriate method. Perhaps you are using an FD value from
another process ?

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[prg.amc]

Hi Thanks for the reply, actually the fd is exported from gbm buffers. using
this fd the downstream element will open the device and it will do memap.
I`m trying to understand can we wrap just DMA fd into gstbuffer ?



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[Nicolas Dufresne-5]

Le jeu. 8 avr. 2021 17 h 30, prg.amc <[hidden email]> a écrit :

Hi Thanks for the reply, actually the fd is exported from gbm buffers. using
this fd the downstream element will open the device and it will do memap.
I`m trying to understand can we wrap just DMA fd into gstbuffer ?

No, since GST buffers are GstMemory container. As I said, the error you reported indicates an invalid FD, I would worry about that fiest and then try and figure out why the memory is being mapped to CPU. GEM prime FD are not always mappable or a supported the video format.

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[prg.amc]

The FD error is due to mmap. I've to pass only fd to wayland sink. In the
code when I wrap it with dmabuff allocator gstreamer is trying to copy data
with memap from fdmemory. Is there a way to stop copy and pass buffer to
wayland sink.



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[Nicolas Dufresne-5]

Le jeudi 08 avril 2021 à 21:26 -0500, prg.amc a écrit :
> The FD error is due to mmap. I've to pass only fd to wayland sink. In the
> code when I wrap it with dmabuff allocator gstreamer is trying to copy data
> with memap from fdmemory. Is there a way to stop copy and pass buffer to
> wayland sink.

As I tried to explain, you need to read the related code that attempt to copy
and understand why a copy is being made. And then fix that to avoid the copy.

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