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core(libva): use dynamic loader#19562

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opencv-pushbot merged 2 commits intoopencv:masterfrom
alalek:libva_dynamic
Feb 19, 2021
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core(libva): use dynamic loader#19562
opencv-pushbot merged 2 commits intoopencv:masterfrom
alalek:libva_dynamic

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@alalek alalek commented Feb 18, 2021 •
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force_builders=Custom
Xbuild_image:Custom=centos:7
build_image:Custom=ubuntu:20.04
buildworker:Custom=linux-1,linux-4,linux-6
allow_multiple_commits=1

@mshabunin
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mshabunin commented Feb 18, 2021

Checked with this MediaStack: https://github.com/Intel-Media-SDK/MediaSDK/releases/tag/intel-mediasdk-20.5.1

Env setup
export LD_LIBRARY_PATH=/opt/intel/mediasdk-20.5.1/lib64/
export LIBVA_DRIVER_NAME=iHD
export LIBVA_DRIVERS_PATH=/opt/intel/mediasdk-20.5.1/lib64/
export PATH=/opt/intel/mediasdk-20.5.1/bin/:$PATH
Running the sample
$ ./bin/example_va_intel_va_intel_interop ../opencv/samples/data/rubberwhale1.p
ng A B
libva info: VA-API version 1.10.0
libva info: User environment variable requested driver 'iHD'
libva info: Trying to open /opt/intel/mediasdk-20.5.1/lib64//iHD_drv_video.so
libva info: Found init function __vaDriverInit_1_10
libva info: va_openDriver() returns 0
VA display opened successfully
Interop ON : processing time, msec: 1.08985

$ ./bin/example_va_intel_va_intel_interop ../opencv/samples/data/rubberwhale1.png A B -f
libva info: VA-API version 1.10.0
libva info: User environment variable requested driver 'iHD'
libva info: Trying to open /opt/intel/mediasdk-20.5.1/lib64//iHD_drv_video.so
libva info: Found init function __vaDriverInit_1_10
libva info: va_openDriver() returns 0
VA display opened successfully
Interop OFF: processing time, msec: 39.3298
No dependency on libva
$ objdump -p lib/libopencv_core.so | grep NEEDED
  NEEDED               libdl.so.2
  NEEDED               libpthread.so.0
  NEEDED               librt.so.1
  NEEDED               libz.so.1
  NEEDED               libstdc++.so.6
  NEEDED               libm.so.6
  NEEDED               libgcc_s.so.1
  NEEDED               libc.so.6

@mikhail-nikolskiy
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mikhail-nikolskiy commented Feb 18, 2021 •
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VADisplay (VAAPI context) contains v-table of all VAAPI functions. VAAPI experts confirm that v-table guarantees backward compatibility.
So all functions, except vaInitilize which creates VADisplay, could be called via v-table if include public header <va/va_backend.h>.
Here is example.

Should be safe to use v-table starting VAAPI 1.0 which dated Oct 21, 2017. Not sure if ok to support only VAAPI>=1.0 in OpenCV, or use universal dlopen()..

VA_MAJOR_VERSION >= 1

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mshabunin commented Feb 19, 2021

@mikhail-nikolskiy , I think the method with vtable requires runtime libva version checks. Otherwise there can be situation when the library built with fresh libva would expect some new method exists and slightly older libva loaded in runtime would not have this field in vtable. This situation is partially handled by dlopen (older version won't load), but not with vtable. So this approach requires slightly more developer's conciousness and double version checks (in general case, not at current integration level):

#if VERSION > XX  // new_function added in XX
if (ctx->version > XX)
    ctx->new_function()
else
#endif
    cerr << "Not implemented" << endl;

We have somewhat similar code for example in OSX AVFoundation integration:

opencv/modules/videoio/src/cap_avfoundation_mac.mm

Lines 330 to 332 in 504ff97

#if defined(__MAC_OS_X_VERSION_MAX_ALLOWED) && __MAC_OS_X_VERSION_MAX_ALLOWED >= 101400
if (@available(macOS 10.14, *))
{

Currently dlopen seems more appropriate since it is compatible with both libva 1.x and 2.x with other things more or less equal.

@alalek
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alalek commented Feb 19, 2021

@mikhail-nikolskiy Thank you for the information!

Unfortunately we still need to support configurations/platforms with old libva versions:

  • CentOS 7: 0.40.0 (by va_version.h)
  • Ubuntu 16.04: 0.39.0

@opencv-pushbot opencv-pushbot merged commit db2cefd into opencv:master Feb 19, 2021
@mshabunin mshabunin mentioned this pull request Feb 24, 2021
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@alalek alalek mentioned this pull request Apr 9, 2021
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