Revert "Epoll compiled on GLIBC only supports GLIBC at runtime (#11722)…

…" (#11738)

Motivation:

It appears we can't do this while also ensuring that working glibc use cases are not impacted.
In particular, there's a musl/glibc compatibility layer which solves the binary compatibility even though musl can still be in the library mappings.

Modifications:

Reverts #11722

Result:

native libs can be used again on alpine with glibc-compat

transport-native-epoll/src/main/c/netty_epoll_native.c

@@ -326,7 +326,6 @@ static jint netty_epoll_native_epollCtlAdd0(JNIEnv* env, jclass clazz, jint efd,
     }
     return res;
 }
-
 static jint netty_epoll_native_epollCtlMod0(JNIEnv* env, jclass clazz, jint efd, jint fd, jint flags) {
     int res = epollCtl(env, efd, EPOLL_CTL_MOD, fd, flags);
     if (res < 0) {
@@ -541,15 +540,6 @@ static jstring netty_epoll_native_kernelVersion(JNIEnv* env, jclass clazz) {
     return NULL;
 }
 
-static jint netty_epoll_native_gnulibc(JNIEnv* env, jclass clazz) {
-#ifdef __GLIBC__
-    return 1;
-#else
-    // We are using an alternative libc, possibly musl but could be anything.
-    return 0;
-#endif // __GLIBC__
-}
-
 static jboolean netty_epoll_native_isSupportingSendmmsg(JNIEnv* env, jclass clazz) {
     if (SYS_sendmmsg == -1) {
         return JNI_FALSE;
@@ -668,8 +658,7 @@ static const JNINativeMethod statically_referenced_fixed_method_table[] = {
   { "isSupportingSendmmsg", "()Z", (void *) netty_epoll_native_isSupportingSendmmsg },
   { "isSupportingRecvmmsg", "()Z", (void *) netty_epoll_native_isSupportingRecvmmsg },
   { "tcpFastopenMode", "()I", (void *) netty_epoll_native_tcpFastopenMode },
-  { "kernelVersion", "()Ljava/lang/String;", (void *) netty_epoll_native_kernelVersion },
-  { "gnulibc", "()I", (void *) netty_epoll_native_gnulibc }
+  { "kernelVersion", "()Ljava/lang/String;", (void *) netty_epoll_native_kernelVersion }
 };
 static const jint statically_referenced_fixed_method_table_size = sizeof(statically_referenced_fixed_method_table) / sizeof(statically_referenced_fixed_method_table[0]);
 static const JNINativeMethod fixed_method_table[] = {

transport-native-epoll/src/main/java/io/netty/channel/epoll/Native.java

@@ -23,15 +23,11 @@
 import io.netty.util.internal.ClassInitializerUtil;
 import io.netty.util.internal.NativeLibraryLoader;
 import io.netty.util.internal.PlatformDependent;
-import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.ThrowableUtil;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
-import java.io.BufferedReader;
-import java.io.FileInputStream;
 import java.io.IOException;
-import java.io.InputStreamReader;
 import java.nio.channels.FileChannel;
 import java.nio.channels.Selector;
 
@@ -40,7 +36,6 @@
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.epollin;
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.epollout;
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.epollrdhup;
-import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.gnulibc;
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.isSupportingRecvmmsg;
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.isSupportingSendmmsg;
 import static io.netty.channel.epoll.NativeStaticallyReferencedJniMethods.kernelVersion;
@@ -55,7 +50,6 @@
  * <p>Static members which call JNI methods must be defined in {@link NativeStaticallyReferencedJniMethods}.
  */
 public final class Native {
-    private static final boolean checkMusl = SystemPropertyUtil.getBoolean("io.netty.native.musl.check", true);
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(Native.class);
 
     static {
@@ -83,9 +77,9 @@ public final class Native {
         );
 
         try {
-            // First, try calling a side effect free JNI method to see if the library was already
+            // First, try calling a side-effect free JNI method to see if the library was already
             // loaded by the application.
-            gnulibc();
+            offsetofEpollData();
         } catch (UnsatisfiedLinkError ignore) {
             // The library was not previously loaded, load it now.
             loadNativeLibrary();
@@ -98,33 +92,6 @@ public final class Native {
                 // Just ignore
             }
         }
-        if (checkMusl && gnulibc() == 1) {
-            // Our binary is compiled for linking with GLIBC.
-            // Let's check that we don't have anything that looks like Musl libc in our runtime.
-            try {
-                FileInputStream fis = new FileInputStream("/proc/self/maps");
-                try {
-                    BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
-                    String line;
-                    while ((line = reader.readLine()) != null) {
-                        if (line.contains("-musl-")) {
-                            throw new LinkageError("Native library was compiled for linking with GLIBC, but GLIBC " +
-                                    "was not found among library mappings. This likely means the OS/JVM uses an " +
-                                    "alternative libc, such as musl. To fix, either use NIO transport, or build a " +
-                                    "native transport for your platform.");
-                        }
-                    }
-                } finally {
-                    try {
-                        fis.close();
-                    } catch (IOException e) {
-                        logger.debug("Failed to close /proc/self/maps file.", e);
-                    }
-                }
-            } catch (IOException e) {
-                logger.debug("Unable to check libc compatibility.", e);
-            }
-        }
         Unix.registerInternal(new Runnable() {
             @Override
             public void run() {

transport-native-epoll/src/main/java/io/netty/channel/epoll/NativeStaticallyReferencedJniMethods.java

@@ -43,5 +43,4 @@ private NativeStaticallyReferencedJniMethods() { }
     static native boolean isSupportingRecvmmsg();
     static native int tcpFastopenMode();
     static native String kernelVersion();
-    static native int gnulibc();
 }