[FFmpeg-devel] [RFC] avdevice: lock to minor version of avformat

[Diederick Niehorster]

As per discussion on the list (
https://ffmpeg.org/pipermail/ffmpeg-devel/2021-June/281513.html, see
especially https://ffmpeg.org/pipermail/ffmpeg-devel/2021-June/281586.html),
to resolve the the unholy ABI-relationship between libavdevice and
libavformat and allow easier working on the part of the avdevice API
that lives in avformat, lock avdevice to a specific major and minor
version of avformat.

Signed-off-by: Diederick Niehorster <dcnieho at gmail.com>
---
 libavdevice/avdevice.c | 10 ++++++++++
 libavdevice/version.h  | 10 ++++++++++
 libavformat/utils.c    |  5 +++++
 libavformat/version.h  | 11 +++++++++++
 libavutil/macros.h     |  2 ++
 5 files changed, 38 insertions(+)

diff --git a/libavdevice/avdevice.c b/libavdevice/avdevice.c
index 8f460c7564..b608ec532f 100644
--- a/libavdevice/avdevice.c
+++ b/libavdevice/avdevice.c
@@ -38,6 +38,16 @@ unsigned avdevice_version(void)
     return LIBAVDEVICE_VERSION_INT;
 }
 
+unsigned avdevice_version_same_minor()
+{
+    // check version of loaded lavf has same major and minor version as
+    // this library was compiled against
+    if ((avformat_version_same_minor()) & ~0xFF != (LIBAVFORMAT_VERSION_INT & ~0xFF))
+        abort();
+
+    return avformat_version();
+}
+
 const char * avdevice_configuration(void)
 {
     return FFMPEG_CONFIGURATION;
diff --git a/libavdevice/version.h b/libavdevice/version.h
index 41f568d6b0..4c511a7f53 100644
--- a/libavdevice/version.h
+++ b/libavdevice/version.h
@@ -26,6 +26,7 @@
  */
 
 #include "libavutil/version.h"
+#include "libavutil/macros.h"
 
 #define LIBAVDEVICE_VERSION_MAJOR  59
 #define LIBAVDEVICE_VERSION_MINOR   1
@@ -48,4 +49,13 @@
  */
 #define FF_API_DEVICE_CAPABILITIES (LIBAVDEVICE_VERSION_MAJOR < 60)
 
+/**
+ * avdevice_version_same_minor() expands to a function with
+ * the same minor and major version it was compiled against
+ * encoded in it. Enables linking locking to the minor version
+ * of other libraries they were compiled against.
+ */
+#define avdevice_version_same_minor AV_MAKE_MAJOR_MINOR_FUNC_NAME(device,LIBAVFORMAT_VERSION_MAJOR,LIBAVFORMAT_VERSION_MINOR)
+unsigned avdevice_version_same_minor();
+
 #endif /* AVDEVICE_VERSION_H */
diff --git a/libavformat/utils.c b/libavformat/utils.c
index 332ba534d2..607a777c3f 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -63,6 +63,11 @@ unsigned avformat_version(void)
     return LIBAVFORMAT_VERSION_INT;
 }
 
+unsigned avformat_version_same_minor()
+{
+    return avformat_version();
+}
+
 const char *avformat_configuration(void)
 {
     return FFMPEG_CONFIGURATION;
diff --git a/libavformat/version.h b/libavformat/version.h
index 379a68cc7c..2423800687 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -28,6 +28,7 @@
  */
 
 #include "libavutil/version.h"
+#include "libavutil/macros.h"
 
 // Major bumping may affect Ticket5467, 5421, 5451(compatibility with Chromium)
 // Also please add any ticket numbers that you believe might be affected here
@@ -63,4 +64,14 @@
 
 
 #define FF_API_R_FRAME_RATE            1
+
+/**
+ * avformat_version_same_minor() expands to a function with
+ * the same minor and major version it was compiled against
+ * encoded in it. Enables linking locking to the minor version
+ * of other libraries they were compiled against. 
+ */
+#define avformat_version_same_minor AV_MAKE_MAJOR_MINOR_FUNC_NAME(format,LIBAVFORMAT_VERSION_MAJOR,LIBAVFORMAT_VERSION_MINOR)
+unsigned avformat_version_same_minor();
+
 #endif /* AVFORMAT_VERSION_H */
diff --git a/libavutil/macros.h b/libavutil/macros.h
index 2a7567c3ea..dda1bf6452 100644
--- a/libavutil/macros.h
+++ b/libavutil/macros.h
@@ -73,6 +73,8 @@
  * @}
  */
 
+#define AV_MAKE_MAJOR_MINOR_FUNC_NAME(name,major,minor) AV_GLUE(av,name)AV_GLUE(_version_,major)AV_GLUE(_,minor)
+
 #define AV_PRAGMA(s) _Pragma(#s)
 
 #define FFALIGN(x, a) (((x)+(a)-1)&~((a)-1))
-- 
2.28.0.windows.1