xref: /libcore/luni/src/main/native/libcore_io_Linux.cpp

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "Posix"

#include "AsynchronousSocketCloseMonitor.h"
#include "JNIHelp.h"
#include "JniConstants.h"
#include "JniException.h"
#include "NetworkUtilities.h"
#include "ScopedBytes.h"
#include "ScopedLocalRef.h"
#include "ScopedPrimitiveArray.h"
#include "ScopedUtfChars.h"
#include "StaticAssert.h"
#include "UniquePtr.h"
#include "toStringArray.h"

#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in.h>
#include <poll.h>
#include <pwd.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/sendfile.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/utsname.h>
#include <sys/vfs.h> // Bionic doesn't have <sys/statvfs.h>
#include <unistd.h>

#define TO_JAVA_STRING(NAME, EXP) \
        jstring NAME = env->NewStringUTF(EXP); \
        if (NAME == NULL) return NULL;

struct addrinfo_deleter {
    void operator()(addrinfo* p) const {
        if (p != NULL) { // bionic's freeaddrinfo(3) crashes when passed NULL.
            freeaddrinfo(p);
        }
    }
};

/**
 * Used to retry syscalls that can return EINTR. This differs from TEMP_FAILURE_RETRY in that
 * it also considers the case where the reason for failure is that another thread called
 * Socket.close.
 *
 * Assumes 'JNIEnv* env' and 'jobject javaFd' (which is a java.io.FileDescriptor) are in scope.
 *
 * Returns the result of 'exp', though a Java exception will be pending if the result is -1.
 *
 * Correct usage looks like this:
 *
 * void Posix_syscall(JNIEnv* env, jobject javaFd, ...) {
 *     ...
 *     int fd;
 *     NET_FAILURE_RETRY("syscall", syscall(fd, ...)); // Throws on error.
 * }
 */
#define NET_FAILURE_RETRY(syscall_name, exp) ({ \
    typeof (exp) _rc = -1; \
    do { \
        { \
            fd = jniGetFDFromFileDescriptor(env, javaFd); \
            AsynchronousSocketCloseMonitor monitor(fd); \
            _rc = (exp); \
        } \
        if (_rc == -1) { \
            if (jniGetFDFromFileDescriptor(env, javaFd) == -1) { \
                jniThrowException(env, "java/net/SocketException", "Socket closed"); \
                break; \
            } else if (errno != EINTR) { \
                throwErrnoException(env, syscall_name); \
                break; \
            } \
        } \
    } while (_rc == -1); \
    _rc; })

static void throwException(JNIEnv* env, jclass exceptionClass, jmethodID ctor3, jmethodID ctor2,
        const char* functionName, int error) {
    jthrowable cause = NULL;
    if (env->ExceptionCheck()) {
        cause = env->ExceptionOccurred();
        env->ExceptionClear();
    }

    ScopedLocalRef<jstring> detailMessage(env, env->NewStringUTF(functionName));
    if (detailMessage.get() == NULL) {
        // Not really much we can do here. We're probably dead in the water,
        // but let's try to stumble on...
        env->ExceptionClear();
    }

    jobject exception;
    if (cause != NULL) {
        exception = env->NewObject(exceptionClass, ctor3, detailMessage.get(), error, cause);
    } else {
        exception = env->NewObject(exceptionClass, ctor2, detailMessage.get(), error);
    }
    env->Throw(reinterpret_cast<jthrowable>(exception));
}

static void throwErrnoException(JNIEnv* env, const char* functionName) {
    int error = errno;
    static jmethodID ctor3 = env->GetMethodID(JniConstants::errnoExceptionClass,
            "<init>", "(Ljava/lang/String;ILjava/lang/Throwable;)V");
    static jmethodID ctor2 = env->GetMethodID(JniConstants::errnoExceptionClass,
            "<init>", "(Ljava/lang/String;I)V");
    throwException(env, JniConstants::errnoExceptionClass, ctor3, ctor2, functionName, error);
}

static void throwGaiException(JNIEnv* env, const char* functionName, int error) {
    if (error == EAI_SYSTEM) {
        // EAI_SYSTEM means "look at errno instead", so we want our GaiException to have the
        // relevant ErrnoException as its cause.
        throwErrnoException(env, functionName);
        // Deliberately fall through to throw another exception...
    }
    static jmethodID ctor3 = env->GetMethodID(JniConstants::gaiExceptionClass,
            "<init>", "(Ljava/lang/String;ILjava/lang/Throwable;)V");
    static jmethodID ctor2 = env->GetMethodID(JniConstants::gaiExceptionClass,
            "<init>", "(Ljava/lang/String;I)V");
    throwException(env, JniConstants::gaiExceptionClass, ctor3, ctor2, functionName, error);
}

template <typename rc_t>
static rc_t throwIfMinusOne(JNIEnv* env, const char* name, rc_t rc) {
    if (rc == rc_t(-1)) {
        throwErrnoException(env, name);
    }
    return rc;
}

template <typename ScopedT>
class IoVec {
public:
    IoVec(JNIEnv* env, size_t bufferCount) : mEnv(env), mBufferCount(bufferCount) {
    }

    bool init(jobjectArray javaBuffers, jintArray javaOffsets, jintArray javaByteCounts) {
        // We can't delete our local references until after the I/O, so make sure we have room.
        if (mEnv->PushLocalFrame(mBufferCount + 16) < 0) {
            return false;
        }
        ScopedIntArrayRO offsets(mEnv, javaOffsets);
        if (offsets.get() == NULL) {
            return false;
        }
        ScopedIntArrayRO byteCounts(mEnv, javaByteCounts);
        if (byteCounts.get() == NULL) {
            return false;
        }
        // TODO: Linux actually has a 1024 buffer limit. glibc works around this, and we should too.
        // TODO: you can query the limit at runtime with sysconf(_SC_IOV_MAX).
        for (size_t i = 0; i < mBufferCount; ++i) {
            jobject buffer = mEnv->GetObjectArrayElement(javaBuffers, i); // We keep this local ref.
            mScopedBuffers.push_back(new ScopedT(mEnv, buffer));
            jbyte* ptr = const_cast<jbyte*>(mScopedBuffers.back()->get());
            if (ptr == NULL) {
                return false;
            }
            struct iovec iov;
            iov.iov_base = reinterpret_cast<void*>(ptr + offsets[i]);
            iov.iov_len = byteCounts[i];
            mIoVec.push_back(iov);
        }
        return true;
    }

    ~IoVec() {
        for (size_t i = 0; i < mScopedBuffers.size(); ++i) {
            delete mScopedBuffers[i];
        }
        mEnv->PopLocalFrame(NULL);
    }

    iovec* get() {
        return &mIoVec[0];
    }

    size_t size() {
        return mBufferCount;
    }

private:
    JNIEnv* mEnv;
    size_t mBufferCount;
    std::vector<iovec> mIoVec;
    std::vector<ScopedT*> mScopedBuffers;
};

static jobject makeInetSocketAddress(JNIEnv* env, const sockaddr_storage* ss, int port) {
    jobject inetAddress = socketAddressToInetAddress(env, ss);
    if (inetAddress == NULL) {
        return NULL;
    }
    static jmethodID ctor = env->GetMethodID(JniConstants::inetSocketAddressClass, "<init>",
            "(Ljava/net/InetAddress;I)V");
    return env->NewObject(JniConstants::inetSocketAddressClass, ctor, inetAddress, port);
}

static jobject makeSocketAddress(JNIEnv* env, const sockaddr_storage* ss) {
    if (ss->ss_family == AF_INET) {
        int port = ntohs(reinterpret_cast<const sockaddr_in*>(ss)->sin_port);
        return makeInetSocketAddress(env, ss, port);
    } else if (ss->ss_family == AF_INET6) {
        int port = ntohs(reinterpret_cast<const sockaddr_in6*>(ss)->sin6_port);
        return makeInetSocketAddress(env, ss, port);
    }
    // TODO: support AF_UNIX and AF_UNSPEC, and have some other behavior for other families
    return NULL;
}

static jobject makeStructPasswd(JNIEnv* env, const struct passwd& pw) {
    TO_JAVA_STRING(pw_name, pw.pw_name);
    TO_JAVA_STRING(pw_dir, pw.pw_dir);
    TO_JAVA_STRING(pw_shell, pw.pw_shell);
    static jmethodID ctor = env->GetMethodID(JniConstants::structPasswdClass, "<init>",
            "(Ljava/lang/String;IILjava/lang/String;Ljava/lang/String;)V");
    return env->NewObject(JniConstants::structPasswdClass, ctor,
            pw_name, static_cast<jint>(pw.pw_uid), static_cast<jint>(pw.pw_gid), pw_dir, pw_shell);
}

static jobject makeStructStat(JNIEnv* env, const struct stat& sb) {
    static jmethodID ctor = env->GetMethodID(JniConstants::structStatClass, "<init>",
            "(JJIJIIJJJJJJJ)V");
    return env->NewObject(JniConstants::structStatClass, ctor,
            static_cast<jlong>(sb.st_dev), static_cast<jlong>(sb.st_ino),
            static_cast<jint>(sb.st_mode), static_cast<jlong>(sb.st_nlink),
            static_cast<jint>(sb.st_uid), static_cast<jint>(sb.st_gid),
            static_cast<jlong>(sb.st_rdev), static_cast<jlong>(sb.st_size),
            static_cast<jlong>(sb.st_atime), static_cast<jlong>(sb.st_mtime),
            static_cast<jlong>(sb.st_ctime), static_cast<jlong>(sb.st_blksize),
            static_cast<jlong>(sb.st_blocks));
}

static jobject makeStructStatFs(JNIEnv* env, const struct statfs& sb) {
    STATIC_ASSERT(sizeof(sb.f_bavail) == sizeof(jlong), statfs_not_64_bit);
    STATIC_ASSERT(sizeof(sb.f_bfree) == sizeof(jlong), statfs_not_64_bit);
    STATIC_ASSERT(sizeof(sb.f_blocks) == sizeof(jlong), statfs_not_64_bit);

    static jmethodID ctor = env->GetMethodID(JniConstants::structStatFsClass, "<init>",
            "(JJJJJJJJ)V");
    return env->NewObject(JniConstants::structStatFsClass, ctor, static_cast<jlong>(sb.f_bsize),
            static_cast<jlong>(sb.f_blocks), static_cast<jlong>(sb.f_bfree),
            static_cast<jlong>(sb.f_bavail), static_cast<jlong>(sb.f_files),
            static_cast<jlong>(sb.f_ffree), static_cast<jlong>(sb.f_namelen),
            static_cast<jlong>(sb.f_frsize));
}

static jobject makeStructLinger(JNIEnv* env, const struct linger& l) {
    static jmethodID ctor = env->GetMethodID(JniConstants::structLingerClass, "<init>", "(II)V");
    return env->NewObject(JniConstants::structLingerClass, ctor, l.l_onoff, l.l_linger);
}

static jobject makeStructTimeval(JNIEnv* env, const struct timeval& tv) {
    static jmethodID ctor = env->GetMethodID(JniConstants::structTimevalClass, "<init>", "(JJ)V");
    return env->NewObject(JniConstants::structTimevalClass, ctor,
            static_cast<jlong>(tv.tv_sec), static_cast<jlong>(tv.tv_usec));
}

static jobject makeStructUtsname(JNIEnv* env, const struct utsname& buf) {
    TO_JAVA_STRING(sysname, buf.sysname);
    TO_JAVA_STRING(nodename, buf.nodename);
    TO_JAVA_STRING(release, buf.release);
    TO_JAVA_STRING(version, buf.version);
    TO_JAVA_STRING(machine, buf.machine);
    static jmethodID ctor = env->GetMethodID(JniConstants::structUtsnameClass, "<init>",
            "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V");
    return env->NewObject(JniConstants::structUtsnameClass, ctor,
            sysname, nodename, release, version, machine);
};

static bool fillIfreq(JNIEnv* env, jstring javaInterfaceName, struct ifreq& req) {
    ScopedUtfChars interfaceName(env, javaInterfaceName);
    if (interfaceName.c_str() == NULL) {
        return false;
    }
    memset(&req, 0, sizeof(req));
    strncpy(req.ifr_name, interfaceName.c_str(), sizeof(req.ifr_name));
    req.ifr_name[sizeof(req.ifr_name) - 1] = '\0';
    return true;
}

static jobject doStat(JNIEnv* env, jstring javaPath, bool isLstat) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return NULL;
    }
    struct stat sb;
    int rc = isLstat ? TEMP_FAILURE_RETRY(lstat(path.c_str(), &sb))
                     : TEMP_FAILURE_RETRY(stat(path.c_str(), &sb));
    if (rc == -1) {
        throwErrnoException(env, isLstat ? "lstat" : "stat");
        return NULL;
    }
    return makeStructStat(env, sb);
}

class Passwd {
public:
    Passwd(JNIEnv* env) : mEnv(env), mResult(NULL) {
        mBufferSize = sysconf(_SC_GETPW_R_SIZE_MAX);
        if (mBufferSize == -1UL) {
            // We're probably on bionic, where 1KiB should be enough for anyone.
            // TODO: fix bionic to return 1024 like glibc.
            mBufferSize = 1024;
        }
        mBuffer.reset(new char[mBufferSize]);
    }

    jobject getpwnam(const char* name) {
        return process("getpwnam_r", getpwnam_r(name, &mPwd, mBuffer.get(), mBufferSize, &mResult));
    }

    jobject getpwuid(uid_t uid) {
        return process("getpwuid_r", getpwuid_r(uid, &mPwd, mBuffer.get(), mBufferSize, &mResult));
    }

    struct passwd* get() {
        return mResult;
    }

private:
    jobject process(const char* syscall, int error) {
        if (mResult == NULL) {
            errno = error;
            throwErrnoException(mEnv, syscall);
            return NULL;
        }
        return makeStructPasswd(mEnv, *mResult);
    }

    JNIEnv* mEnv;
    UniquePtr<char[]> mBuffer;
    size_t mBufferSize;
    struct passwd mPwd;
    struct passwd* mResult;
};

static jboolean Posix_access(JNIEnv* env, jobject, jstring javaPath, jint mode) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return JNI_FALSE;
    }
    int rc = TEMP_FAILURE_RETRY(access(path.c_str(), mode));
    if (rc == -1) {
        throwErrnoException(env, "access");
    }
    return (rc == 0);
}

static void Posix_bind(JNIEnv* env, jobject, jobject javaFd, jobject javaAddress, jint port) {
    sockaddr_storage ss;
    if (!inetAddressToSockaddr(env, javaAddress, port, &ss)) {
        return;
    }
    int fd;
    const sockaddr* sa = reinterpret_cast<const sockaddr*>(&ss);
    NET_FAILURE_RETRY("bind", bind(fd, sa, sizeof(sockaddr_storage)));
}

static void Posix_chmod(JNIEnv* env, jobject, jstring javaPath, jint mode) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return;
    }
    throwIfMinusOne(env, "chmod", TEMP_FAILURE_RETRY(chmod(path.c_str(), mode)));
}

static void Posix_close(JNIEnv* env, jobject, jobject javaFd) {
    // Get the FileDescriptor's 'fd' field and clear it.
    // We need to do this before we can throw an IOException (http://b/3222087).
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    jniSetFileDescriptorOfFD(env, javaFd, -1);

    // Even if close(2) fails with EINTR, the fd will have been closed.
    // Using TEMP_FAILURE_RETRY will either lead to EBADF or closing someone else's fd.
    // http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
    throwIfMinusOne(env, "close", close(fd));
}

static void Posix_connect(JNIEnv* env, jobject, jobject javaFd, jobject javaAddress, jint port) {
    sockaddr_storage ss;
    if (!inetAddressToSockaddr(env, javaAddress, port, &ss)) {
        return;
    }
    int fd;
    const sockaddr* sa = reinterpret_cast<const sockaddr*>(&ss);
    NET_FAILURE_RETRY("connect", connect(fd, sa, sizeof(sockaddr_storage)));
}

static jobject Posix_dup(JNIEnv* env, jobject, jobject javaOldFd) {
    int oldFd = jniGetFDFromFileDescriptor(env, javaOldFd);
    int newFd = throwIfMinusOne(env, "dup", TEMP_FAILURE_RETRY(dup(oldFd)));
    return (newFd != -1) ? jniCreateFileDescriptor(env, newFd) : NULL;
}

static jobject Posix_dup2(JNIEnv* env, jobject, jobject javaOldFd, jint newFd) {
    int oldFd = jniGetFDFromFileDescriptor(env, javaOldFd);
    int fd = throwIfMinusOne(env, "dup2", TEMP_FAILURE_RETRY(dup2(oldFd, newFd)));
    return (fd != -1) ? jniCreateFileDescriptor(env, fd) : NULL;
}

static jobjectArray Posix_environ(JNIEnv* env, jobject) {
    extern char** environ; // Standard, but not in any header file.
    return toStringArray(env, environ);
}

static jint Posix_fcntlVoid(JNIEnv* env, jobject, jobject javaFd, jint cmd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "fcntl", TEMP_FAILURE_RETRY(fcntl(fd, cmd)));
}

static jint Posix_fcntlLong(JNIEnv* env, jobject, jobject javaFd, jint cmd, jlong arg) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "fcntl", TEMP_FAILURE_RETRY(fcntl(fd, cmd, arg)));
}

static jint Posix_fcntlFlock(JNIEnv* env, jobject, jobject javaFd, jint cmd, jobject javaFlock) {
    static jfieldID typeFid = env->GetFieldID(JniConstants::structFlockClass, "l_type", "S");
    static jfieldID whenceFid = env->GetFieldID(JniConstants::structFlockClass, "l_whence", "S");
    static jfieldID startFid = env->GetFieldID(JniConstants::structFlockClass, "l_start", "J");
    static jfieldID lenFid = env->GetFieldID(JniConstants::structFlockClass, "l_len", "J");
    static jfieldID pidFid = env->GetFieldID(JniConstants::structFlockClass, "l_pid", "I");

    struct flock64 lock;
    memset(&lock, 0, sizeof(lock));
    lock.l_type = env->GetShortField(javaFlock, typeFid);
    lock.l_whence = env->GetShortField(javaFlock, whenceFid);
    lock.l_start = env->GetLongField(javaFlock, startFid);
    lock.l_len = env->GetLongField(javaFlock, lenFid);
    lock.l_pid = env->GetIntField(javaFlock, pidFid);

    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    int rc = throwIfMinusOne(env, "fcntl", TEMP_FAILURE_RETRY(fcntl(fd, cmd, &lock)));
    if (rc != -1) {
        env->SetShortField(javaFlock, typeFid, lock.l_type);
        env->SetShortField(javaFlock, whenceFid, lock.l_whence);
        env->SetLongField(javaFlock, startFid, lock.l_start);
        env->SetLongField(javaFlock, lenFid, lock.l_len);
        env->SetIntField(javaFlock, pidFid, lock.l_pid);
    }
    return rc;
}

static void Posix_fdatasync(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "fdatasync", TEMP_FAILURE_RETRY(fdatasync(fd)));
}

static jobject Posix_fstat(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct stat sb;
    int rc = TEMP_FAILURE_RETRY(fstat(fd, &sb));
    if (rc == -1) {
        throwErrnoException(env, "fstat");
        return NULL;
    }
    return makeStructStat(env, sb);
}

static jobject Posix_fstatfs(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct statfs sb;
    int rc = TEMP_FAILURE_RETRY(fstatfs(fd, &sb));
    if (rc == -1) {
        throwErrnoException(env, "fstatfs");
        return NULL;
    }
    return makeStructStatFs(env, sb);
}

static void Posix_fsync(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "fsync", TEMP_FAILURE_RETRY(fsync(fd)));
}

static void Posix_ftruncate(JNIEnv* env, jobject, jobject javaFd, jlong length) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "ftruncate", TEMP_FAILURE_RETRY(ftruncate64(fd, length)));
}

static jstring Posix_gai_strerror(JNIEnv* env, jobject, jint error) {
    return env->NewStringUTF(gai_strerror(error));
}

static jobjectArray Posix_getaddrinfo(JNIEnv* env, jobject, jstring javaNode, jobject javaHints) {
    ScopedUtfChars node(env, javaNode);
    if (node.c_str() == NULL) {
        return NULL;
    }

    static jfieldID flagsFid = env->GetFieldID(JniConstants::structAddrinfoClass, "ai_flags", "I");
    static jfieldID familyFid = env->GetFieldID(JniConstants::structAddrinfoClass, "ai_family", "I");
    static jfieldID socktypeFid = env->GetFieldID(JniConstants::structAddrinfoClass, "ai_socktype", "I");
    static jfieldID protocolFid = env->GetFieldID(JniConstants::structAddrinfoClass, "ai_protocol", "I");

    addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_flags = env->GetIntField(javaHints, flagsFid);
    hints.ai_family = env->GetIntField(javaHints, familyFid);
    hints.ai_socktype = env->GetIntField(javaHints, socktypeFid);
    hints.ai_protocol = env->GetIntField(javaHints, protocolFid);

    addrinfo* addressList = NULL;
    int rc = getaddrinfo(node.c_str(), NULL, &hints, &addressList);
    UniquePtr<addrinfo, addrinfo_deleter> addressListDeleter(addressList);
    if (rc != 0) {
        throwGaiException(env, "getaddrinfo", rc);
        return NULL;
    }

    // Count results so we know how to size the output array.
    int addressCount = 0;
    for (addrinfo* ai = addressList; ai != NULL; ai = ai->ai_next) {
        if (ai->ai_family == AF_INET || ai->ai_family == AF_INET6) {
            ++addressCount;
        } else {
            LOGE("getaddrinfo unexpected ai_family %i", ai->ai_family);
        }
    }
    if (addressCount == 0) {
        return NULL;
    }

    // Prepare output array.
    jobjectArray result = env->NewObjectArray(addressCount, JniConstants::inetAddressClass, NULL);
    if (result == NULL) {
        return NULL;
    }

    // Examine returned addresses one by one, save them in the output array.
    int index = 0;
    for (addrinfo* ai = addressList; ai != NULL; ai = ai->ai_next) {
        if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6) {
            // Unknown address family. Skip this address.
            LOGE("getaddrinfo unexpected ai_family %i", ai->ai_family);
            continue;
        }

        // Convert each IP address into a Java byte array.
        sockaddr_storage* address = reinterpret_cast<sockaddr_storage*>(ai->ai_addr);
        ScopedLocalRef<jobject> inetAddress(env, socketAddressToInetAddress(env, address));
        if (inetAddress.get() == NULL) {
            return NULL;
        }
        env->SetObjectArrayElement(result, index, inetAddress.get());
        ++index;
    }
    return result;
}

static jint Posix_getegid(JNIEnv*, jobject) {
    return getegid();
}

static jint Posix_geteuid(JNIEnv*, jobject) {
    return geteuid();
}

static jint Posix_getgid(JNIEnv*, jobject) {
    return getgid();
}

static jstring Posix_getenv(JNIEnv* env, jobject, jstring javaName) {
    ScopedUtfChars name(env, javaName);
    if (name.c_str() == NULL) {
        return NULL;
    }
    return env->NewStringUTF(getenv(name.c_str()));
}

static jstring Posix_getnameinfo(JNIEnv* env, jobject, jobject javaAddress, jint flags) {
    sockaddr_storage ss;
    if (!inetAddressToSockaddr_getnameinfo(env, javaAddress, 0, &ss)) {
        return NULL;
    }
    // TODO: bionic's getnameinfo(3) seems to want its length parameter to be exactly
    // sizeof(sockaddr_in) for an IPv4 address and sizeof (sockaddr_in6) for an
    // IPv6 address. Fix getnameinfo so it accepts sizeof(sockaddr_storage), and
    // then remove this hack.
    socklen_t size = (ss.ss_family == AF_INET) ? sizeof(sockaddr_in) : sizeof(sockaddr_in6);
    char buf[NI_MAXHOST]; // NI_MAXHOST is longer than INET6_ADDRSTRLEN.
    int rc = getnameinfo(reinterpret_cast<sockaddr*>(&ss), size, buf, sizeof(buf), NULL, 0, flags);
    if (rc != 0) {
        throwGaiException(env, "getnameinfo", rc);
        return NULL;
    }
    return env->NewStringUTF(buf);
}

static jint Posix_getpid(JNIEnv*, jobject) {
    return getpid();
}

static jint Posix_getppid(JNIEnv*, jobject) {
    return getppid();
}

static jobject Posix_getpwnam(JNIEnv* env, jobject, jstring javaName) {
    ScopedUtfChars name(env, javaName);
    if (name.c_str() == NULL) {
        return NULL;
    }
    return Passwd(env).getpwnam(name.c_str());
}

static jobject Posix_getpwuid(JNIEnv* env, jobject, jint uid) {
    return Passwd(env).getpwuid(uid);
}

static jobject Posix_getsockname(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    sockaddr_storage ss;
    sockaddr* sa = reinterpret_cast<sockaddr*>(&ss);
    socklen_t byteCount = sizeof(ss);
    memset(&ss, 0, byteCount);
    int rc = TEMP_FAILURE_RETRY(getsockname(fd, sa, &byteCount));
    if (rc == -1) {
        throwErrnoException(env, "getsockname");
        return NULL;
    }
    return makeSocketAddress(env, &ss);
}

static jint Posix_getsockoptByte(JNIEnv* env, jobject, jobject javaFd, jint level, jint option) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    u_char result = 0;
    socklen_t size = sizeof(result);
    throwIfMinusOne(env, "getsockopt", TEMP_FAILURE_RETRY(getsockopt(fd, level, option, &result, &size)));
    return result;
}

static jobject Posix_getsockoptInAddr(JNIEnv* env, jobject, jobject javaFd, jint level, jint option) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    sockaddr_storage ss;
    memset(&ss, 0, sizeof(ss));
    ss.ss_family = AF_INET; // This is only for the IPv4-only IP_MULTICAST_IF.
    sockaddr_in* sa = reinterpret_cast<sockaddr_in*>(&ss);
    socklen_t size = sizeof(sa->sin_addr);
    int rc = TEMP_FAILURE_RETRY(getsockopt(fd, level, option, &sa->sin_addr, &size));
    if (rc == -1) {
        throwErrnoException(env, "getsockopt");
        return NULL;
    }
    return socketAddressToInetAddress(env, &ss);
}

static jint Posix_getsockoptInt(JNIEnv* env, jobject, jobject javaFd, jint level, jint option) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    jint result = 0;
    socklen_t size = sizeof(result);
    throwIfMinusOne(env, "getsockopt", TEMP_FAILURE_RETRY(getsockopt(fd, level, option, &result, &size)));
    return result;
}

static jobject Posix_getsockoptLinger(JNIEnv* env, jobject, jobject javaFd, jint level, jint option) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct linger l;
    socklen_t size = sizeof(l);
    memset(&l, 0, size);
    int rc = TEMP_FAILURE_RETRY(getsockopt(fd, level, option, &l, &size));
    if (rc == -1) {
        throwErrnoException(env, "getsockopt");
        return NULL;
    }
    return makeStructLinger(env, l);
}

static jobject Posix_getsockoptTimeval(JNIEnv* env, jobject, jobject javaFd, jint level, jint option) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct timeval tv;
    socklen_t size = sizeof(tv);
    memset(&tv, 0, size);
    int rc = TEMP_FAILURE_RETRY(getsockopt(fd, level, option, &tv, &size));
    if (rc == -1) {
        throwErrnoException(env, "getsockopt");
        return NULL;
    }
    return makeStructTimeval(env, tv);
}

static jint Posix_getuid(JNIEnv*, jobject) {
    return getuid();
}

static jstring Posix_if_indextoname(JNIEnv* env, jobject, jint index) {
    char buf[IF_NAMESIZE];
    char* name = if_indextoname(index, buf);
    // if_indextoname(3) returns NULL on failure, which will come out of NewStringUTF unscathed.
    // There's no useful information in errno, so we don't bother throwing. Callers can null-check.
    return env->NewStringUTF(name);
}

static jobject Posix_inet_aton(JNIEnv* env, jobject, jstring javaName) {
    ScopedUtfChars name(env, javaName);
    if (name.c_str() == NULL) {
        return NULL;
    }
    sockaddr_storage ss;
    memset(&ss, 0, sizeof(ss));
    sockaddr_in* sin = reinterpret_cast<sockaddr_in*>(&ss);
    if (inet_aton(name.c_str(), &sin->sin_addr) == 0) {
        return NULL;
    }
    sin->sin_family = AF_INET; // inet_aton only supports IPv4.
    return socketAddressToInetAddress(env, &ss);
}

static jobject Posix_ioctlInetAddress(JNIEnv* env, jobject, jobject javaFd, jint cmd, jstring javaInterfaceName) {
    struct ifreq req;
    if (!fillIfreq(env, javaInterfaceName, req)) {
        return NULL;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    int rc = throwIfMinusOne(env, "ioctl", TEMP_FAILURE_RETRY(ioctl(fd, cmd, &req)));
    if (rc == -1) {
        return NULL;
    }
    return socketAddressToInetAddress(env, reinterpret_cast<sockaddr_storage*>(&req.ifr_addr));
}

static jint Posix_ioctlInt(JNIEnv* env, jobject, jobject javaFd, jint cmd, jobject javaArg) {
    // This is complicated because ioctls may return their result by updating their argument
    // or via their return value, so we need to support both.
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    static jfieldID valueFid = env->GetFieldID(JniConstants::mutableIntClass, "value", "I");
    jint arg = env->GetIntField(javaArg, valueFid);
    int rc = throwIfMinusOne(env, "ioctl", TEMP_FAILURE_RETRY(ioctl(fd, cmd, &arg)));
    if (!env->ExceptionCheck()) {
        env->SetIntField(javaArg, valueFid, arg);
    }
    return rc;
}

static jboolean Posix_isatty(JNIEnv* env, jobject, jobject javaFd) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return TEMP_FAILURE_RETRY(isatty(fd)) == 0;
}

static void Posix_kill(JNIEnv* env, jobject, jint pid, jint sig) {
    throwIfMinusOne(env, "kill", TEMP_FAILURE_RETRY(kill(pid, sig)));
}

static void Posix_listen(JNIEnv* env, jobject, jobject javaFd, jint backlog) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "listen", TEMP_FAILURE_RETRY(listen(fd, backlog)));
}

static jlong Posix_lseek(JNIEnv* env, jobject, jobject javaFd, jlong offset, jint whence) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "lseek", TEMP_FAILURE_RETRY(lseek64(fd, offset, whence)));
}

static jobject Posix_lstat(JNIEnv* env, jobject, jstring javaPath) {
    return doStat(env, javaPath, true);
}

static void Posix_mincore(JNIEnv* env, jobject, jlong address, jlong byteCount, jbyteArray javaVector) {
    ScopedByteArrayRW vector(env, javaVector);
    if (vector.get() == NULL) {
        return;
    }
    void* ptr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    unsigned char* vec = reinterpret_cast<unsigned char*>(vector.get());
    throwIfMinusOne(env, "mincore", TEMP_FAILURE_RETRY(mincore(ptr, byteCount, vec)));
}

static void Posix_mkdir(JNIEnv* env, jobject, jstring javaPath, jint mode) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return;
    }
    throwIfMinusOne(env, "mkdir", TEMP_FAILURE_RETRY(mkdir(path.c_str(), mode)));
}

static void Posix_mlock(JNIEnv* env, jobject, jlong address, jlong byteCount) {
    void* ptr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    throwIfMinusOne(env, "mlock", TEMP_FAILURE_RETRY(mlock(ptr, byteCount)));
}

static jlong Posix_mmap(JNIEnv* env, jobject, jlong address, jlong byteCount, jint prot, jint flags, jobject javaFd, jlong offset) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    void* suggestedPtr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    void* ptr = mmap(suggestedPtr, byteCount, prot, flags, fd, offset);
    if (ptr == MAP_FAILED) {
        throwErrnoException(env, "mmap");
    }
    return static_cast<jlong>(reinterpret_cast<uintptr_t>(ptr));
}

static void Posix_msync(JNIEnv* env, jobject, jlong address, jlong byteCount, jint flags) {
    void* ptr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    throwIfMinusOne(env, "msync", TEMP_FAILURE_RETRY(msync(ptr, byteCount, flags)));
}

static void Posix_munlock(JNIEnv* env, jobject, jlong address, jlong byteCount) {
    void* ptr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    throwIfMinusOne(env, "munlock", TEMP_FAILURE_RETRY(munlock(ptr, byteCount)));
}

static void Posix_munmap(JNIEnv* env, jobject, jlong address, jlong byteCount) {
    void* ptr = reinterpret_cast<void*>(static_cast<uintptr_t>(address));
    throwIfMinusOne(env, "munmap", TEMP_FAILURE_RETRY(munmap(ptr, byteCount)));
}

static jobject Posix_open(JNIEnv* env, jobject, jstring javaPath, jint flags, jint mode) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return NULL;
    }
    int fd = throwIfMinusOne(env, "open", TEMP_FAILURE_RETRY(open(path.c_str(), flags, mode)));
    return fd != -1 ? jniCreateFileDescriptor(env, fd) : NULL;
}

static jobjectArray Posix_pipe(JNIEnv* env, jobject) {
    int fds[2];
    throwIfMinusOne(env, "pipe", TEMP_FAILURE_RETRY(pipe(&fds[0])));
    jobjectArray result = env->NewObjectArray(2, JniConstants::fileDescriptorClass, NULL);
    if (result == NULL) {
        return NULL;
    }
    for (int i = 0; i < 2; ++i) {
        ScopedLocalRef<jobject> fd(env, jniCreateFileDescriptor(env, fds[i]));
        if (fd.get() == NULL) {
            return NULL;
        }
        env->SetObjectArrayElement(result, i, fd.get());
        if (env->ExceptionCheck()) {
            return NULL;
        }
    }
    return result;
}

static jint Posix_poll(JNIEnv* env, jobject, jobjectArray javaStructs, jint timeoutMs) {
    static jfieldID fdFid = env->GetFieldID(JniConstants::structPollfdClass, "fd", "Ljava/io/FileDescriptor;");
    static jfieldID eventsFid = env->GetFieldID(JniConstants::structPollfdClass, "events", "S");
    static jfieldID reventsFid = env->GetFieldID(JniConstants::structPollfdClass, "revents", "S");

    // Turn the Java libcore.io.StructPollfd[] into a C++ struct pollfd[].
    size_t arrayLength = env->GetArrayLength(javaStructs);
    UniquePtr<struct pollfd[]> fds(new struct pollfd[arrayLength]);
    memset(fds.get(), 0, sizeof(struct pollfd) * arrayLength);
    size_t count = 0; // Some trailing array elements may be irrelevant. (See below.)
    for (size_t i = 0; i < arrayLength; ++i) {
        ScopedLocalRef<jobject> javaStruct(env, env->GetObjectArrayElement(javaStructs, i));
        if (javaStruct.get() == NULL) {
            break; // We allow trailing nulls in the array for caller convenience.
        }
        ScopedLocalRef<jobject> javaFd(env, env->GetObjectField(javaStruct.get(), fdFid));
        if (javaFd.get() == NULL) {
            break; // We also allow callers to just clear the fd field (this is what Selector does).
        }
        fds[count].fd = jniGetFDFromFileDescriptor(env, javaFd.get());
        fds[count].events = env->GetShortField(javaStruct.get(), eventsFid);
        ++count;
    }

    int rc = TEMP_FAILURE_RETRY(poll(fds.get(), count, timeoutMs));
    if (rc == -1) {
        throwErrnoException(env, "poll");
        return -1;
    }

    // Update the revents fields in the Java libcore.io.StructPollfd[].
    for (size_t i = 0; i < count; ++i) {
        ScopedLocalRef<jobject> javaStruct(env, env->GetObjectArrayElement(javaStructs, i));
        if (javaStruct.get() == NULL) {
            return -1;
        }
        env->SetShortField(javaStruct.get(), reventsFid, fds[i].revents);
    }
    return rc;
}

static jint Posix_readBytes(JNIEnv* env, jobject, jobject javaFd, jobject javaBytes, jint byteOffset, jint byteCount) {
    ScopedBytesRW bytes(env, javaBytes);
    if (bytes.get() == NULL) {
        return -1;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "read", TEMP_FAILURE_RETRY(read(fd, bytes.get() + byteOffset, byteCount)));
}

static jint Posix_readv(JNIEnv* env, jobject, jobject javaFd, jobjectArray buffers, jintArray offsets, jintArray byteCounts) {
    IoVec<ScopedBytesRW> ioVec(env, env->GetArrayLength(buffers));
    if (!ioVec.init(buffers, offsets, byteCounts)) {
        return -1;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "readv", TEMP_FAILURE_RETRY(readv(fd, ioVec.get(), ioVec.size())));
}

static void Posix_remove(JNIEnv* env, jobject, jstring javaPath) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return;
    }
    throwIfMinusOne(env, "remove", TEMP_FAILURE_RETRY(remove(path.c_str())));
}

static void Posix_rename(JNIEnv* env, jobject, jstring javaOldPath, jstring javaNewPath) {
    ScopedUtfChars oldPath(env, javaOldPath);
    if (oldPath.c_str() == NULL) {
        return;
    }
    ScopedUtfChars newPath(env, javaNewPath);
    if (newPath.c_str() == NULL) {
        return;
    }
    throwIfMinusOne(env, "rename", TEMP_FAILURE_RETRY(rename(oldPath.c_str(), newPath.c_str())));
}

static jlong Posix_sendfile(JNIEnv* env, jobject, jobject javaOutFd, jobject javaInFd, jobject javaOffset, jlong byteCount) {
    int outFd = jniGetFDFromFileDescriptor(env, javaOutFd);
    int inFd = jniGetFDFromFileDescriptor(env, javaInFd);
    static jfieldID valueFid = env->GetFieldID(JniConstants::mutableLongClass, "value", "J");
    off_t offset = 0;
    off_t* offsetPtr = NULL;
    if (javaOffset != NULL) {
        // TODO: fix bionic so we can have a 64-bit off_t!
        offset = env->GetLongField(javaOffset, valueFid);
        offsetPtr = &offset;
    }
    jlong result = throwIfMinusOne(env, "sendfile", TEMP_FAILURE_RETRY(sendfile(outFd, inFd, offsetPtr, byteCount)));
    if (javaOffset != NULL) {
        env->SetLongField(javaOffset, valueFid, offset);
    }
    return result;
}

static void Posix_setegid(JNIEnv* env, jobject, jint egid) {
    throwIfMinusOne(env, "setegid", TEMP_FAILURE_RETRY(setegid(egid)));
}

static void Posix_seteuid(JNIEnv* env, jobject, jint euid) {
    throwIfMinusOne(env, "seteuid", TEMP_FAILURE_RETRY(seteuid(euid)));
}

static void Posix_setgid(JNIEnv* env, jobject, jint gid) {
    throwIfMinusOne(env, "setgid", TEMP_FAILURE_RETRY(setgid(gid)));
}

static void Posix_setsockoptByte(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jint value) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    u_char byte = value;
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &byte, sizeof(byte))));
}

static void Posix_setsockoptIfreq(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jstring javaInterfaceName) {
    struct ifreq req;
    if (!fillIfreq(env, javaInterfaceName, req)) {
        return;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &req, sizeof(req))));
}

static void Posix_setsockoptInt(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jint value) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &value, sizeof(value))));
}

static void Posix_setsockoptIpMreqn(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jint value) {
    ip_mreqn req;
    memset(&req, 0, sizeof(req));
    req.imr_ifindex = value;
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &req, sizeof(req))));
}

static void Posix_setsockoptGroupReq(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jobject javaGroupReq) {
    struct group_req value;

    static jfieldID grInterfaceFid = env->GetFieldID(JniConstants::structGroupReqClass, "gr_interface", "I");
    value.gr_interface = env->GetIntField(javaGroupReq, grInterfaceFid);
    // Get the IPv4 or IPv6 multicast address to join or leave.
    static jfieldID grGroupFid = env->GetFieldID(JniConstants::structGroupReqClass, "gr_group", "Ljava/net/InetAddress;");
    ScopedLocalRef<jobject> javaGroup(env, env->GetObjectField(javaGroupReq, grGroupFid));
    if (!inetAddressToSockaddr(env, javaGroup.get(), 0, &value.gr_group)) {
        return;
    }

    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    int rc = TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &value, sizeof(value)));
    if (rc == -1 && errno == EINVAL) {
        // Maybe we're a 32-bit binary talking to a 64-bit kernel?
        // glibc doesn't automatically handle this.
        struct GCC_HIDDEN group_req64 {
            uint32_t gr_interface;
            uint32_t my_padding;
            sockaddr_storage gr_group;
        };
        group_req64 value64;
        value64.gr_interface = value.gr_interface;
        memcpy(&value64.gr_group, &value.gr_group, sizeof(value.gr_group));
        rc = TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &value64, sizeof(value64)));
    }
    throwIfMinusOne(env, "setsockopt", rc);
}

static void Posix_setsockoptLinger(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jobject javaLinger) {
    static jfieldID lOnoffFid = env->GetFieldID(JniConstants::structLingerClass, "l_onoff", "I");
    static jfieldID lLingerFid = env->GetFieldID(JniConstants::structLingerClass, "l_linger", "I");
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct linger value;
    value.l_onoff = env->GetIntField(javaLinger, lOnoffFid);
    value.l_linger = env->GetIntField(javaLinger, lLingerFid);
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &value, sizeof(value))));
}

static void Posix_setsockoptTimeval(JNIEnv* env, jobject, jobject javaFd, jint level, jint option, jobject javaTimeval) {
    static jfieldID tvSecFid = env->GetFieldID(JniConstants::structTimevalClass, "tv_sec", "J");
    static jfieldID tvUsecFid = env->GetFieldID(JniConstants::structTimevalClass, "tv_usec", "J");
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    struct timeval value;
    value.tv_sec = env->GetIntField(javaTimeval, tvSecFid);
    value.tv_usec = env->GetIntField(javaTimeval, tvUsecFid);
    throwIfMinusOne(env, "setsockopt", TEMP_FAILURE_RETRY(setsockopt(fd, level, option, &value, sizeof(value))));
}

static void Posix_setuid(JNIEnv* env, jobject, jint uid) {
    throwIfMinusOne(env, "setuid", TEMP_FAILURE_RETRY(setuid(uid)));
}

static void Posix_shutdown(JNIEnv* env, jobject, jobject javaFd, jint how) {
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    throwIfMinusOne(env, "shutdown", TEMP_FAILURE_RETRY(shutdown(fd, how)));
}

static jobject Posix_socket(JNIEnv* env, jobject, jint domain, jint type, jint protocol) {
    int fd = throwIfMinusOne(env, "socket", TEMP_FAILURE_RETRY(socket(domain, type, protocol)));
    return fd != -1 ? jniCreateFileDescriptor(env, fd) : NULL;
}

static jobject Posix_stat(JNIEnv* env, jobject, jstring javaPath) {
    return doStat(env, javaPath, false);
}

static jobject Posix_statfs(JNIEnv* env, jobject, jstring javaPath) {
    ScopedUtfChars path(env, javaPath);
    if (path.c_str() == NULL) {
        return NULL;
    }
    struct statfs sb;
    int rc = TEMP_FAILURE_RETRY(statfs(path.c_str(), &sb));
    if (rc == -1) {
        throwErrnoException(env, "statfs");
        return NULL;
    }
    return makeStructStatFs(env, sb);
}

static jstring Posix_strerror(JNIEnv* env, jobject, jint errnum) {
    char buffer[BUFSIZ];
    const char* message = jniStrError(errnum, buffer, sizeof(buffer));
    return env->NewStringUTF(message);
}

static void Posix_symlink(JNIEnv* env, jobject, jstring javaOldPath, jstring javaNewPath) {
    ScopedUtfChars oldPath(env, javaOldPath);
    if (oldPath.c_str() == NULL) {
        return;
    }
    ScopedUtfChars newPath(env, javaNewPath);
    if (newPath.c_str() == NULL) {
        return;
    }
    throwIfMinusOne(env, "symlink", TEMP_FAILURE_RETRY(symlink(oldPath.c_str(), newPath.c_str())));
}

static jlong Posix_sysconf(JNIEnv* env, jobject, jint name) {
    // Since -1 is a valid result from sysconf(3), detecting failure is a little more awkward.
    errno = 0;
    long result = sysconf(name);
    if (result == -1L && errno == EINVAL) {
        throwErrnoException(env, "sysconf");
    }
    return result;
}

static jobject Posix_uname(JNIEnv* env, jobject) {
    struct utsname buf;
    if (throwIfMinusOne(env, "uname", TEMP_FAILURE_RETRY(uname(&buf))) == -1) {
        return NULL;
    }
    return makeStructUtsname(env, buf);
}

static jint Posix_writeBytes(JNIEnv* env, jobject, jobject javaFd, jbyteArray javaBytes, jint byteOffset, jint byteCount) {
    ScopedBytesRO bytes(env, javaBytes);
    if (bytes.get() == NULL) {
        return -1;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "write", TEMP_FAILURE_RETRY(write(fd, bytes.get() + byteOffset, byteCount)));
}

static jint Posix_writev(JNIEnv* env, jobject, jobject javaFd, jobjectArray buffers, jintArray offsets, jintArray byteCounts) {
    IoVec<ScopedBytesRO> ioVec(env, env->GetArrayLength(buffers));
    if (!ioVec.init(buffers, offsets, byteCounts)) {
        return -1;
    }
    int fd = jniGetFDFromFileDescriptor(env, javaFd);
    return throwIfMinusOne(env, "writev", TEMP_FAILURE_RETRY(writev(fd, ioVec.get(), ioVec.size())));
}

static JNINativeMethod gMethods[] = {
    NATIVE_METHOD(Posix, access, "(Ljava/lang/String;I)Z"),
    NATIVE_METHOD(Posix, bind, "(Ljava/io/FileDescriptor;Ljava/net/InetAddress;I)V"),
    NATIVE_METHOD(Posix, chmod, "(Ljava/lang/String;I)V"),
    NATIVE_METHOD(Posix, close, "(Ljava/io/FileDescriptor;)V"),
    NATIVE_METHOD(Posix, connect, "(Ljava/io/FileDescriptor;Ljava/net/InetAddress;I)V"),
    NATIVE_METHOD(Posix, dup, "(Ljava/io/FileDescriptor;)Ljava/io/FileDescriptor;"),
    NATIVE_METHOD(Posix, dup2, "(Ljava/io/FileDescriptor;I)Ljava/io/FileDescriptor;"),
    NATIVE_METHOD(Posix, environ, "()[Ljava/lang/String;"),
    NATIVE_METHOD(Posix, fcntlVoid, "(Ljava/io/FileDescriptor;I)I"),
    NATIVE_METHOD(Posix, fcntlLong, "(Ljava/io/FileDescriptor;IJ)I"),
    NATIVE_METHOD(Posix, fcntlFlock, "(Ljava/io/FileDescriptor;ILlibcore/io/StructFlock;)I"),
    NATIVE_METHOD(Posix, fdatasync, "(Ljava/io/FileDescriptor;)V"),
    NATIVE_METHOD(Posix, fstat, "(Ljava/io/FileDescriptor;)Llibcore/io/StructStat;"),
    NATIVE_METHOD(Posix, fstatfs, "(Ljava/io/FileDescriptor;)Llibcore/io/StructStatFs;"),
    NATIVE_METHOD(Posix, fsync, "(Ljava/io/FileDescriptor;)V"),
    NATIVE_METHOD(Posix, ftruncate, "(Ljava/io/FileDescriptor;J)V"),
    NATIVE_METHOD(Posix, gai_strerror, "(I)Ljava/lang/String;"),
    NATIVE_METHOD(Posix, getaddrinfo, "(Ljava/lang/String;Llibcore/io/StructAddrinfo;)[Ljava/net/InetAddress;"),
    NATIVE_METHOD(Posix, getegid, "()I"),
    NATIVE_METHOD(Posix, geteuid, "()I"),
    NATIVE_METHOD(Posix, getgid, "()I"),
    NATIVE_METHOD(Posix, getenv, "(Ljava/lang/String;)Ljava/lang/String;"),
    NATIVE_METHOD(Posix, getnameinfo, "(Ljava/net/InetAddress;I)Ljava/lang/String;"),
    NATIVE_METHOD(Posix, getpid, "()I"),
    NATIVE_METHOD(Posix, getppid, "()I"),
    NATIVE_METHOD(Posix, getpwnam, "(Ljava/lang/String;)Llibcore/io/StructPasswd;"),
    NATIVE_METHOD(Posix, getpwuid, "(I)Llibcore/io/StructPasswd;"),
    NATIVE_METHOD(Posix, getsockname, "(Ljava/io/FileDescriptor;)Ljava/net/SocketAddress;"),
    NATIVE_METHOD(Posix, getsockoptByte, "(Ljava/io/FileDescriptor;II)I"),
    NATIVE_METHOD(Posix, getsockoptInAddr, "(Ljava/io/FileDescriptor;II)Ljava/net/InetAddress;"),
    NATIVE_METHOD(Posix, getsockoptInt, "(Ljava/io/FileDescriptor;II)I"),
    NATIVE_METHOD(Posix, getsockoptLinger, "(Ljava/io/FileDescriptor;II)Llibcore/io/StructLinger;"),
    NATIVE_METHOD(Posix, getsockoptTimeval, "(Ljava/io/FileDescriptor;II)Llibcore/io/StructTimeval;"),
    NATIVE_METHOD(Posix, getuid, "()I"),
    NATIVE_METHOD(Posix, if_indextoname, "(I)Ljava/lang/String;"),
    NATIVE_METHOD(Posix, inet_aton, "(Ljava/lang/String;)Ljava/net/InetAddress;"),
    NATIVE_METHOD(Posix, ioctlInetAddress, "(Ljava/io/FileDescriptor;ILjava/lang/String;)Ljava/net/InetAddress;"),
    NATIVE_METHOD(Posix, ioctlInt, "(Ljava/io/FileDescriptor;ILlibcore/util/MutableInt;)I"),
    NATIVE_METHOD(Posix, isatty, "(Ljava/io/FileDescriptor;)Z"),
    NATIVE_METHOD(Posix, kill, "(II)V"),
    NATIVE_METHOD(Posix, listen, "(Ljava/io/FileDescriptor;I)V"),
    NATIVE_METHOD(Posix, lseek, "(Ljava/io/FileDescriptor;JI)J"),
    NATIVE_METHOD(Posix, lstat, "(Ljava/lang/String;)Llibcore/io/StructStat;"),
    NATIVE_METHOD(Posix, mincore, "(JJ[B)V"),
    NATIVE_METHOD(Posix, mkdir, "(Ljava/lang/String;I)V"),
    NATIVE_METHOD(Posix, mlock, "(JJ)V"),
    NATIVE_METHOD(Posix, mmap, "(JJIILjava/io/FileDescriptor;J)J"),
    NATIVE_METHOD(Posix, msync, "(JJI)V"),
    NATIVE_METHOD(Posix, munlock, "(JJ)V"),
    NATIVE_METHOD(Posix, munmap, "(JJ)V"),
    NATIVE_METHOD(Posix, open, "(Ljava/lang/String;II)Ljava/io/FileDescriptor;"),
    NATIVE_METHOD(Posix, pipe, "()[Ljava/io/FileDescriptor;"),
    NATIVE_METHOD(Posix, poll, "([Llibcore/io/StructPollfd;I)I"),
    NATIVE_METHOD(Posix, readBytes, "(Ljava/io/FileDescriptor;Ljava/lang/Object;II)I"),
    NATIVE_METHOD(Posix, readv, "(Ljava/io/FileDescriptor;[Ljava/lang/Object;[I[I)I"),
    NATIVE_METHOD(Posix, remove, "(Ljava/lang/String;)V"),
    NATIVE_METHOD(Posix, rename, "(Ljava/lang/String;Ljava/lang/String;)V"),
    NATIVE_METHOD(Posix, sendfile, "(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;Llibcore/util/MutableLong;J)J"),
    NATIVE_METHOD(Posix, setegid, "(I)V"),
    NATIVE_METHOD(Posix, seteuid, "(I)V"),
    NATIVE_METHOD(Posix, setgid, "(I)V"),
    NATIVE_METHOD(Posix, setsockoptByte, "(Ljava/io/FileDescriptor;III)V"),
    NATIVE_METHOD(Posix, setsockoptIfreq, "(Ljava/io/FileDescriptor;IILjava/lang/String;)V"),
    NATIVE_METHOD(Posix, setsockoptInt, "(Ljava/io/FileDescriptor;III)V"),
    NATIVE_METHOD(Posix, setsockoptIpMreqn, "(Ljava/io/FileDescriptor;III)V"),
    NATIVE_METHOD(Posix, setsockoptGroupReq, "(Ljava/io/FileDescriptor;IILlibcore/io/StructGroupReq;)V"),
    NATIVE_METHOD(Posix, setsockoptLinger, "(Ljava/io/FileDescriptor;IILlibcore/io/StructLinger;)V"),
    NATIVE_METHOD(Posix, setsockoptTimeval, "(Ljava/io/FileDescriptor;IILlibcore/io/StructTimeval;)V"),
    NATIVE_METHOD(Posix, setuid, "(I)V"),
    NATIVE_METHOD(Posix, shutdown, "(Ljava/io/FileDescriptor;I)V"),
    NATIVE_METHOD(Posix, socket, "(III)Ljava/io/FileDescriptor;"),
    NATIVE_METHOD(Posix, stat, "(Ljava/lang/String;)Llibcore/io/StructStat;"),
    NATIVE_METHOD(Posix, statfs, "(Ljava/lang/String;)Llibcore/io/StructStatFs;"),
    NATIVE_METHOD(Posix, strerror, "(I)Ljava/lang/String;"),
    NATIVE_METHOD(Posix, symlink, "(Ljava/lang/String;Ljava/lang/String;)V"),
    NATIVE_METHOD(Posix, sysconf, "(I)J"),
    NATIVE_METHOD(Posix, uname, "()Llibcore/io/StructUtsname;"),
    NATIVE_METHOD(Posix, writeBytes, "(Ljava/io/FileDescriptor;Ljava/lang/Object;II)I"),
    NATIVE_METHOD(Posix, writev, "(Ljava/io/FileDescriptor;[Ljava/lang/Object;[I[I)I"),
};
int register_libcore_io_Posix(JNIEnv* env) {
    return jniRegisterNativeMethods(env, "libcore/io/Posix", gMethods, NELEM(gMethods));
}