52954ff505
This change adds support for 32 bit kernels by capping mProducerPos to 4 bytes. mConsumerPos (which is written to by userspace) continues to use 8 bytes. (This can be done because an entire page is allocated for mConsumerPos to control access permissions). In a 32 bit kernel, that means that the top order bits are just ignored. In addition, comparisons in userspace only use the bottom 4 bytes to be bitness agnostic. Test: atest BpfRingbufTest Change-Id: I7fe6d9000a151512785f1aa2a53fa97d31967d19
JNI
As a general rule, jarjar every static library dependency used in a mainline module into the modules's namespace (especially if it is also used by other modules)
Fully-qualified name of java class needs to be hard-coded into the JNI .so, because JNI_OnLoad does not take any parameters. This means that there needs to be a different .so target for each post-jarjared package, so for each module.
This is the guideline to provide JNI library shared with modules:
-
provide a common java library in frameworks/libs/net with the Java class (e.g. BpfMap.java).
-
provide a common native library in frameworks/libs/net with the JNI and provide the native register function with class_name parameter. See register_com_android_net_module_util_BpfMap function in frameworks/libs/net/common/native/bpfmapjni/com_android_net_module_util_BpfMap.cpp as an example.
When you want to use JNI library from frameworks/lib/net:
-
Each module includes the java library (e.g. net-utils-device-common-bpf) and applies its jarjar rules after build.
-
Each module creates a native library in their directory, which statically links against the common native library (e.g. libnet_utils_device_common_bpf), and calls the native registered function by hardcoding the post-jarjar class_name. Linkage MUST be static because common functions in the file (e.g.,
register_com_android_net_module_util_BpfMap) will appear in the library (.so) file, and different versions of the library loaded in the same process by different modules will in general have different versions. It's important that each of these libraries loads the common function from its own library. Static linkage should guarantee this because static linkage resolves symbols at build time, not runtime.