Backport ParcelFileDescriptor.createPipe() from master.

This allows content providers to expose arbitraty data
through the ContentResolver open* APIs.

Change-Id: I408a0b7cee9cdba5654a962098386c012d6b3549

api/current.xml

@@ -126818,6 +126818,19 @@
 <exception name="IOException" type="java.io.IOException">
 </exception>
 </method>
+<method name="createPipe"
+ return="android.os.ParcelFileDescriptor[]"
+ abstract="false"
+ native="false"
+ synchronized="false"
+ static="true"
+ final="false"
+ deprecated="not deprecated"
+ visibility="public"
+>
+<exception name="IOException" type="java.io.IOException">
+</exception>
+</method>
 <method name="describeContents"
  return="int"
  abstract="false"

core/java/android/os/ParcelFileDescriptor.java

@@ -133,6 +133,25 @@ public class ParcelFileDescriptor implements Parcelable {
     // Extracts the file descriptor from the specified socket and returns it untouched
     private static native FileDescriptor getFileDescriptorFromSocket(Socket socket);
 
+    /**
+     * Create two ParcelFileDescriptors structured as a data pipe.  The first
+     * ParcelFileDescriptor in the returned array is the read side; the second
+     * is the write side.
+     */
+    public static ParcelFileDescriptor[] createPipe() throws IOException {
+        FileDescriptor[] fds = new FileDescriptor[2];
+        int res = createPipeNative(fds);
+        if (res == 0) {
+            ParcelFileDescriptor[] pfds = new ParcelFileDescriptor[2];
+            pfds[0] = new ParcelFileDescriptor(fds[0]);
+            pfds[1] = new ParcelFileDescriptor(fds[1]);
+            return pfds;
+        }
+        throw new IOException("Unable to create pipe: errno=" + -res);
+    }
+
+    private static native int createPipeNative(FileDescriptor[] outFds);
+
     /**
      * Retrieve the actual FileDescriptor associated with this object.
      * 

core/jni/android_os_ParcelFileDescriptor.cpp

@@ -66,6 +66,26 @@ static jobject android_os_ParcelFileDescriptor_getFileDescriptorFromSocket(JNIEn
     return fileDescriptorClone;
 }
 
+static int android_os_ParcelFileDescriptor_createPipeNative(JNIEnv* env,
+    jobject clazz, jobjectArray outFds)
+{
+    int fds[2];
+    if (pipe(fds) < 0) {
+        return -errno;
+    }
+
+    for (int i=0; i<2; i++) {
+        jobject fdObj = env->NewObject(gFileDescriptorOffsets.mClass,
+                gFileDescriptorOffsets.mConstructor);
+        if (fdObj != NULL) {
+            env->SetIntField(fdObj, gFileDescriptorOffsets.mDescriptor, fds[i]);
+        }
+        env->SetObjectArrayElement(outFds, i, fdObj);
+    }
+
+    return 0;
+}
+
 static jint getFd(JNIEnv* env, jobject clazz)
 {
     jobject descriptor = env->GetObjectField(clazz, gParcelFileDescriptorOffsets.mFileDescriptor);
@@ -109,6 +129,8 @@ static jlong android_os_ParcelFileDescriptor_seekTo(JNIEnv* env,
 static const JNINativeMethod gParcelFileDescriptorMethods[] = {
     {"getFileDescriptorFromSocket", "(Ljava/net/Socket;)Ljava/io/FileDescriptor;",
         (void*)android_os_ParcelFileDescriptor_getFileDescriptorFromSocket},
+    {"createPipeNative", "([Ljava/io/FileDescriptor;)I",
+        (void*)android_os_ParcelFileDescriptor_createPipeNative},
     {"getStatSize", "()J",
         (void*)android_os_ParcelFileDescriptor_getStatSize},
     {"seekTo", "(J)J",