UNIXProcess_md.c 28.2 KB
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/*
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 * Copyright 1995-2008 Sun Microsystems, Inc.  All Rights Reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

#undef  _LARGEFILE64_SOURCE
#define _LARGEFILE64_SOURCE 1

#include "jni.h"
#include "jvm.h"
#include "jvm_md.h"
#include "jni_util.h"
#include "io_util.h"

/*
 * Platform-specific support for java.lang.Process
 */
#include <assert.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/types.h>
#include <ctype.h>
#include <wait.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <dirent.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>

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/*
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 * There are 3 possible strategies we might use to "fork":
 *
 * - fork(2).  Very portable and reliable but subject to
 *   failure due to overcommit (see the documentation on
 *   /proc/sys/vm/overcommit_memory in Linux proc(5)).
 *   This is the ancient problem of spurious failure whenever a large
 *   process starts a small subprocess.
 *
 * - vfork().  Using this is scary because all relevant man pages
 *   contain dire warnings, e.g. Linux vfork(2).  But at least it's
 *   documented in the glibc docs and is standardized by XPG4.
 *   http://www.opengroup.org/onlinepubs/000095399/functions/vfork.html
 *   On Linux, one might think that vfork() would be implemented using
 *   the clone system call with flag CLONE_VFORK, but in fact vfork is
 *   a separate system call (which is a good sign, suggesting that
 *   vfork will continue to be supported at least on Linux).
 *   Another good sign is that glibc implements posix_spawn using
 *   vfork whenever possible.  Note that we cannot use posix_spawn
 *   ourselves because there's no reliable way to close all inherited
 *   file descriptors.
 *
 * - clone() with flags CLONE_VM but not CLONE_THREAD.  clone() is
 *   Linux-specific, but this ought to work - at least the glibc
 *   sources contain code to handle different combinations of CLONE_VM
 *   and CLONE_THREAD.  However, when this was implemented, it
 *   appeared to fail on 32-bit i386 (but not 64-bit x86_64) Linux with
 *   the simple program
 *     Runtime.getRuntime().exec("/bin/true").waitFor();
 *   with:
 *     #  Internal Error (os_linux_x86.cpp:683), pid=19940, tid=2934639536
 *     #  Error: pthread_getattr_np failed with errno = 3 (ESRCH)
 *   We believe this is a glibc bug, reported here:
 *     http://sources.redhat.com/bugzilla/show_bug.cgi?id=10311
 *   but the glibc maintainers closed it as WONTFIX.
 *
 * Based on the above analysis, we are currently using vfork() on
 * Linux and fork() on other Unix systems, but the code to use clone()
 * remains.
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 */

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#define START_CHILD_USE_CLONE 0  /* clone() currently disabled; see above. */

#ifndef START_CHILD_USE_CLONE
  #ifdef __linux__
    #define START_CHILD_USE_CLONE 1
  #else
    #define START_CHILD_USE_CLONE 0
  #endif
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#endif
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/* By default, use vfork() on Linux. */
#ifndef START_CHILD_USE_VFORK
  #ifdef __linux__
    #define START_CHILD_USE_VFORK 1
  #else
    #define START_CHILD_USE_VFORK 0
  #endif
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#endif

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#if START_CHILD_USE_CLONE
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#include <sched.h>
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#define START_CHILD_SYSTEM_CALL "clone"
#elif START_CHILD_USE_VFORK
#define START_CHILD_SYSTEM_CALL "vfork"
#else
#define START_CHILD_SYSTEM_CALL "fork"
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#endif

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#ifndef STDIN_FILENO
#define STDIN_FILENO 0
#endif

#ifndef STDOUT_FILENO
#define STDOUT_FILENO 1
#endif

#ifndef STDERR_FILENO
#define STDERR_FILENO 2
#endif

#ifndef SA_NOCLDSTOP
#define SA_NOCLDSTOP 0
#endif

#ifndef SA_RESTART
#define SA_RESTART 0
#endif

#define FAIL_FILENO (STDERR_FILENO + 1)

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/* TODO: Refactor. */
#define RESTARTABLE(_cmd, _result) do { \
  do { \
    _result = _cmd; \
  } while((_result == -1) && (errno == EINTR)); \
} while(0)

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/* This is one of the rare times it's more portable to declare an
 * external symbol explicitly, rather than via a system header.
 * The declaration is standardized as part of UNIX98, but there is
 * no standard (not even de-facto) header file where the
 * declaration is to be found.  See:
 * http://www.opengroup.org/onlinepubs/009695399/functions/environ.html
 * http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_02.html
 *
 * "All identifiers in this volume of IEEE Std 1003.1-2001, except
 * environ, are defined in at least one of the headers" (!)
 */
extern char **environ;


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static void
setSIGCHLDHandler(JNIEnv *env)
{
    /* There is a subtle difference between having the signal handler
     * for SIGCHLD be SIG_DFL and SIG_IGN.  We cannot obtain process
     * termination information for child processes if the signal
     * handler is SIG_IGN.  It must be SIG_DFL.
     *
     * We used to set the SIGCHLD handler only on Linux, but it's
     * safest to set it unconditionally.
     *
     * Consider what happens if java's parent process sets the SIGCHLD
     * handler to SIG_IGN.  Normally signal handlers are inherited by
     * children, but SIGCHLD is a controversial case.  Solaris appears
     * to always reset it to SIG_DFL, but this behavior may be
     * non-standard-compliant, and we shouldn't rely on it.
     *
     * References:
     * http://www.opengroup.org/onlinepubs/7908799/xsh/exec.html
     * http://www.pasc.org/interps/unofficial/db/p1003.1/pasc-1003.1-132.html
     */
    struct sigaction sa;
    sa.sa_handler = SIG_DFL;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
    if (sigaction(SIGCHLD, &sa, NULL) < 0)
        JNU_ThrowInternalError(env, "Can't set SIGCHLD handler");
}

static void*
xmalloc(JNIEnv *env, size_t size)
{
    void *p = malloc(size);
    if (p == NULL)
        JNU_ThrowOutOfMemoryError(env, NULL);
    return p;
}

#define NEW(type, n) ((type *) xmalloc(env, (n) * sizeof(type)))

/**
 * If PATH is not defined, the OS provides some default value.
 * Unfortunately, there's no portable way to get this value.
 * Fortunately, it's only needed if the child has PATH while we do not.
 */
static const char*
defaultPath(void)
{
#ifdef __solaris__
    /* These really are the Solaris defaults! */
    return (geteuid() == 0 || getuid() == 0) ?
        "/usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin:/usr/sbin" :
        "/usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin:";
#else
    return ":/bin:/usr/bin";    /* glibc */
#endif
}

static const char*
effectivePath(void)
{
    const char *s = getenv("PATH");
    return (s != NULL) ? s : defaultPath();
}

static int
countOccurrences(const char *s, char c)
{
    int count;
    for (count = 0; *s != '\0'; s++)
        count += (*s == c);
    return count;
}

static const char * const *
splitPath(JNIEnv *env, const char *path)
{
    const char *p, *q;
    char **pathv;
    int i;
    int count = countOccurrences(path, ':') + 1;

    pathv = NEW(char*, count+1);
    pathv[count] = NULL;
    for (p = path, i = 0; i < count; i++, p = q + 1) {
        for (q = p; (*q != ':') && (*q != '\0'); q++)
            ;
        if (q == p)             /* empty PATH component => "." */
            pathv[i] = "./";
        else {
            int addSlash = ((*(q - 1)) != '/');
            pathv[i] = NEW(char, q - p + addSlash + 1);
            memcpy(pathv[i], p, q - p);
            if (addSlash)
                pathv[i][q - p] = '/';
            pathv[i][q - p + addSlash] = '\0';
        }
    }
    return (const char * const *) pathv;
}

/**
 * Cached value of JVM's effective PATH.
 * (We don't support putenv("PATH=...") in native code)
 */
static const char *parentPath;

/**
 * Split, canonicalized version of parentPath
 */
static const char * const *parentPathv;

static jfieldID field_exitcode;

JNIEXPORT void JNICALL
Java_java_lang_UNIXProcess_initIDs(JNIEnv *env, jclass clazz)
{
    field_exitcode = (*env)->GetFieldID(env, clazz, "exitcode", "I");

    parentPath  = effectivePath();
    parentPathv = splitPath(env, parentPath);

    setSIGCHLDHandler(env);
}


#ifndef WIFEXITED
#define WIFEXITED(status) (((status)&0xFF) == 0)
#endif

#ifndef WEXITSTATUS
#define WEXITSTATUS(status) (((status)>>8)&0xFF)
#endif

#ifndef WIFSIGNALED
#define WIFSIGNALED(status) (((status)&0xFF) > 0 && ((status)&0xFF00) == 0)
#endif

#ifndef WTERMSIG
#define WTERMSIG(status) ((status)&0x7F)
#endif

/* Block until a child process exits and return its exit code.
   Note, can only be called once for any given pid. */
JNIEXPORT jint JNICALL
Java_java_lang_UNIXProcess_waitForProcessExit(JNIEnv* env,
                                              jobject junk,
                                              jint pid)
{
    /* We used to use waitid() on Solaris, waitpid() on Linux, but
     * waitpid() is more standard, so use it on all POSIX platforms. */
    int status;
    /* Wait for the child process to exit.  This returns immediately if
       the child has already exited. */
    while (waitpid(pid, &status, 0) < 0) {
        switch (errno) {
        case ECHILD: return 0;
        case EINTR: break;
        default: return -1;
        }
    }

    if (WIFEXITED(status)) {
        /*
         * The child exited normally; get its exit code.
         */
        return WEXITSTATUS(status);
    } else if (WIFSIGNALED(status)) {
        /* The child exited because of a signal.
         * The best value to return is 0x80 + signal number,
         * because that is what all Unix shells do, and because
         * it allows callers to distinguish between process exit and
         * process death by signal.
         * Unfortunately, the historical behavior on Solaris is to return
         * the signal number, and we preserve this for compatibility. */
#ifdef __solaris__
        return WTERMSIG(status);
#else
        return 0x80 + WTERMSIG(status);
#endif
    } else {
        /*
         * Unknown exit code; pass it through.
         */
        return status;
    }
}

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static ssize_t
restartableWrite(int fd, const void *buf, size_t count)
{
    ssize_t result;
    RESTARTABLE(write(fd, buf, count), result);
    return result;
}

static int
restartableDup2(int fd_from, int fd_to)
{
    int err;
    RESTARTABLE(dup2(fd_from, fd_to), err);
    return err;
}

static int
restartableClose(int fd)
{
    int err;
    RESTARTABLE(close(fd), err);
    return err;
}

static int
closeSafely(int fd)
{
    return (fd == -1) ? 0 : restartableClose(fd);
}

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static int
isAsciiDigit(char c)
{
  return c >= '0' && c <= '9';
}

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static int
closeDescriptors(void)
{
    DIR *dp;
    struct dirent64 *dirp;
    int from_fd = FAIL_FILENO + 1;

    /* We're trying to close all file descriptors, but opendir() might
     * itself be implemented using a file descriptor, and we certainly
     * don't want to close that while it's in use.  We assume that if
     * opendir() is implemented using a file descriptor, then it uses
     * the lowest numbered file descriptor, just like open().  So we
     * close a couple explicitly.  */

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    restartableClose(from_fd);          /* for possible use by opendir() */
    restartableClose(from_fd + 1);      /* another one for good luck */
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    if ((dp = opendir("/proc/self/fd")) == NULL)
        return 0;

    /* We use readdir64 instead of readdir to work around Solaris bug
     * 6395699: /proc/self/fd fails to report file descriptors >= 1024 on Solaris 9
     */
    while ((dirp = readdir64(dp)) != NULL) {
        int fd;
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        if (isAsciiDigit(dirp->d_name[0]) &&
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            (fd = strtol(dirp->d_name, NULL, 10)) >= from_fd + 2)
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            restartableClose(fd);
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    }

    closedir(dp);

    return 1;
}

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static int
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moveDescriptor(int fd_from, int fd_to)
{
    if (fd_from != fd_to) {
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        if ((restartableDup2(fd_from, fd_to) == -1) ||
            (restartableClose(fd_from) == -1))
            return -1;
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    }
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    return 0;
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}

static const char *
getBytes(JNIEnv *env, jbyteArray arr)
{
    return arr == NULL ? NULL :
        (const char*) (*env)->GetByteArrayElements(env, arr, NULL);
}

static void
releaseBytes(JNIEnv *env, jbyteArray arr, const char* parr)
{
    if (parr != NULL)
        (*env)->ReleaseByteArrayElements(env, arr, (jbyte*) parr, JNI_ABORT);
}

static void
initVectorFromBlock(const char**vector, const char* block, int count)
{
    int i;
    const char *p;
    for (i = 0, p = block; i < count; i++) {
        /* Invariant: p always points to the start of a C string. */
        vector[i] = p;
        while (*(p++));
    }
    vector[count] = NULL;
}

static void
throwIOException(JNIEnv *env, int errnum, const char *defaultDetail)
{
    static const char * const format = "error=%d, %s";
    const char *detail = defaultDetail;
    char *errmsg;
    jstring s;

    if (errnum != 0) {
        const char *s = strerror(errnum);
        if (strcmp(s, "Unknown error") != 0)
            detail = s;
    }
    /* ASCII Decimal representation uses 2.4 times as many bits as binary. */
    errmsg = NEW(char, strlen(format) + strlen(detail) + 3 * sizeof(errnum));
    sprintf(errmsg, format, errnum, detail);
    s = JNU_NewStringPlatform(env, errmsg);
    if (s != NULL) {
        jobject x = JNU_NewObjectByName(env, "java/io/IOException",
                                        "(Ljava/lang/String;)V", s);
        if (x != NULL)
            (*env)->Throw(env, x);
    }
    free(errmsg);
}

#ifdef DEBUG_PROCESS
/* Debugging process code is difficult; where to write debug output? */
static void
debugPrint(char *format, ...)
{
    FILE *tty = fopen("/dev/tty", "w");
    va_list ap;
    va_start(ap, format);
    vfprintf(tty, format, ap);
    va_end(ap);
    fclose(tty);
}
#endif /* DEBUG_PROCESS */

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/**
 * Exec FILE as a traditional Bourne shell script (i.e. one without #!).
 * If we could do it over again, we would probably not support such an ancient
 * misfeature, but compatibility wins over sanity.  The original support for
 * this was imported accidentally from execvp().
 */
static void
execve_as_traditional_shell_script(const char *file,
                                   const char *argv[],
                                   const char *const envp[])
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{
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    /* Use the extra word of space provided for us in argv by caller. */
    const char *argv0 = argv[0];
    const char *const *end = argv;
    while (*end != NULL)
        ++end;
    memmove(argv+2, argv+1, (end-argv) * sizeof (*end));
    argv[0] = "/bin/sh";
    argv[1] = file;
    execve(argv[0], (char **) argv, (char **) envp);
    /* Can't even exec /bin/sh?  Big trouble, but let's soldier on... */
    memmove(argv+1, argv+2, (end-argv) * sizeof (*end));
    argv[0] = argv0;
}

/**
 * Like execve(2), except that in case of ENOEXEC, FILE is assumed to
 * be a shell script and the system default shell is invoked to run it.
 */
static void
execve_with_shell_fallback(const char *file,
                           const char *argv[],
                           const char *const envp[])
{
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#if START_CHILD_USE_CLONE || START_CHILD_USE_VFORK
    /* shared address space; be very careful. */
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    execve(file, (char **) argv, (char **) envp);
    if (errno == ENOEXEC)
        execve_as_traditional_shell_script(file, argv, envp);
#else
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    /* unshared address space; we can mutate environ. */
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    environ = (char **) envp;
    execvp(file, (char **) argv);
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#endif
}

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/**
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 * 'execvpe' should have been included in the Unix standards,
 * and is a GNU extension in glibc 2.10.
 *
 * JDK_execvpe is identical to execvp, except that the child environment is
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 * specified via the 3rd argument instead of being inherited from environ.
 */
static void
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JDK_execvpe(const char *file,
            const char *argv[],
            const char *const envp[])
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{
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    if (envp == NULL || (char **) envp == environ) {
        execvp(file, (char **) argv);
        return;
    }
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    if (*file == '\0') {
        errno = ENOENT;
        return;
    }
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    if (strchr(file, '/') != NULL) {
        execve_with_shell_fallback(file, argv, envp);
    } else {
        /* We must search PATH (parent's, not child's) */
        char expanded_file[PATH_MAX];
        int filelen = strlen(file);
        int sticky_errno = 0;
        const char * const * dirs;
        for (dirs = parentPathv; *dirs; dirs++) {
            const char * dir = *dirs;
            int dirlen = strlen(dir);
            if (filelen + dirlen + 1 >= PATH_MAX) {
                errno = ENAMETOOLONG;
                continue;
            }
            memcpy(expanded_file, dir, dirlen);
            memcpy(expanded_file + dirlen, file, filelen);
            expanded_file[dirlen + filelen] = '\0';
            execve_with_shell_fallback(expanded_file, argv, envp);
            /* There are 3 responses to various classes of errno:
             * return immediately, continue (especially for ENOENT),
             * or continue with "sticky" errno.
             *
             * From exec(3):
             *
             * If permission is denied for a file (the attempted
             * execve returned EACCES), these functions will continue
             * searching the rest of the search path.  If no other
             * file is found, however, they will return with the
             * global variable errno set to EACCES.
             */
            switch (errno) {
            case EACCES:
                sticky_errno = errno;
                /* FALLTHRU */
            case ENOENT:
            case ENOTDIR:
#ifdef ELOOP
            case ELOOP:
#endif
#ifdef ESTALE
            case ESTALE:
#endif
#ifdef ENODEV
            case ENODEV:
#endif
#ifdef ETIMEDOUT
            case ETIMEDOUT:
#endif
                break; /* Try other directories in PATH */
            default:
                return;
            }
        }
        if (sticky_errno != 0)
            errno = sticky_errno;
    }
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}

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/*
 * Reads nbyte bytes from file descriptor fd into buf,
 * The read operation is retried in case of EINTR or partial reads.
 *
 * Returns number of bytes read (normally nbyte, but may be less in
 * case of EOF).  In case of read errors, returns -1 and sets errno.
 */
static ssize_t
readFully(int fd, void *buf, size_t nbyte)
{
    ssize_t remaining = nbyte;
    for (;;) {
        ssize_t n = read(fd, buf, remaining);
        if (n == 0) {
            return nbyte - remaining;
        } else if (n > 0) {
            remaining -= n;
            if (remaining <= 0)
                return nbyte;
            /* We were interrupted in the middle of reading the bytes.
             * Unlikely, but possible. */
            buf = (void *) (((char *)buf) + n);
        } else if (errno == EINTR) {
            /* Strange signals like SIGJVM1 are possible at any time.
             * See http://www.dreamsongs.com/WorseIsBetter.html */
        } else {
            return -1;
        }
    }
}

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typedef struct _ChildStuff
{
    int in[2];
    int out[2];
    int err[2];
    int fail[2];
    int fds[3];
    const char **argv;
    const char **envv;
    const char *pdir;
    jboolean redirectErrorStream;
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#if START_CHILD_USE_CLONE
    void *clone_stack;
#endif
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} ChildStuff;

static void
copyPipe(int from[2], int to[2])
{
    to[0] = from[0];
    to[1] = from[1];
}

/**
 * Child process after a successful fork() or clone().
 * This function must not return, and must be prepared for either all
 * of its address space to be shared with its parent, or to be a copy.
 * It must not modify global variables such as "environ".
 */
static int
childProcess(void *arg)
{
    const ChildStuff* p = (const ChildStuff*) arg;

    /* Close the parent sides of the pipes.
       Closing pipe fds here is redundant, since closeDescriptors()
       would do it anyways, but a little paranoia is a good thing. */
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    if ((closeSafely(p->in[1])   == -1) ||
        (closeSafely(p->out[0])  == -1) ||
        (closeSafely(p->err[0])  == -1) ||
        (closeSafely(p->fail[0]) == -1))
        goto WhyCantJohnnyExec;
701 702 703

    /* Give the child sides of the pipes the right fileno's. */
    /* Note: it is possible for in[0] == 0 */
704 705 706 707 708
    if ((moveDescriptor(p->in[0] != -1 ?  p->in[0] : p->fds[0],
                        STDIN_FILENO) == -1) ||
        (moveDescriptor(p->out[1]!= -1 ? p->out[1] : p->fds[1],
                        STDOUT_FILENO) == -1))
        goto WhyCantJohnnyExec;
709 710

    if (p->redirectErrorStream) {
711 712 713
        if ((closeSafely(p->err[1]) == -1) ||
            (restartableDup2(STDOUT_FILENO, STDERR_FILENO) == -1))
            goto WhyCantJohnnyExec;
714
    } else {
715 716 717
        if (moveDescriptor(p->err[1] != -1 ? p->err[1] : p->fds[2],
                           STDERR_FILENO) == -1)
            goto WhyCantJohnnyExec;
718 719
    }

720 721
    if (moveDescriptor(p->fail[1], FAIL_FILENO) == -1)
        goto WhyCantJohnnyExec;
722 723 724 725

    /* close everything */
    if (closeDescriptors() == 0) { /* failed,  close the old way */
        int max_fd = (int)sysconf(_SC_OPEN_MAX);
726 727 728 729
        int fd;
        for (fd = FAIL_FILENO + 1; fd < max_fd; fd++)
            if (restartableClose(fd) == -1 && errno != EBADF)
                goto WhyCantJohnnyExec;
730 731 732 733 734 735 736 737 738
    }

    /* change to the new working directory */
    if (p->pdir != NULL && chdir(p->pdir) < 0)
        goto WhyCantJohnnyExec;

    if (fcntl(FAIL_FILENO, F_SETFD, FD_CLOEXEC) == -1)
        goto WhyCantJohnnyExec;

739
    JDK_execvpe(p->argv[0], p->argv, p->envv);
740 741 742 743 744 745 746 747 748 749 750 751 752 753

 WhyCantJohnnyExec:
    /* We used to go to an awful lot of trouble to predict whether the
     * child would fail, but there is no reliable way to predict the
     * success of an operation without *trying* it, and there's no way
     * to try a chdir or exec in the parent.  Instead, all we need is a
     * way to communicate any failure back to the parent.  Easy; we just
     * send the errno back to the parent over a pipe in case of failure.
     * The tricky thing is, how do we communicate the *success* of exec?
     * We use FD_CLOEXEC together with the fact that a read() on a pipe
     * yields EOF when the write ends (we have two of them!) are closed.
     */
    {
        int errnum = errno;
754
        restartableWrite(FAIL_FILENO, &errnum, sizeof(errnum));
755
    }
756
    restartableClose(FAIL_FILENO);
757 758 759
    _exit(-1);
    return 0;  /* Suppress warning "no return value from function" */
}
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761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809
/**
 * Start a child process running function childProcess.
 * This function only returns in the parent.
 * We are unusually paranoid; use of clone/vfork is
 * especially likely to tickle gcc/glibc bugs.
 */
#ifdef __attribute_noinline__  /* See: sys/cdefs.h */
__attribute_noinline__
#endif
static pid_t
startChild(ChildStuff *c) {
#if START_CHILD_USE_CLONE
#define START_CHILD_CLONE_STACK_SIZE (64 * 1024)
    /*
     * See clone(2).
     * Instead of worrying about which direction the stack grows, just
     * allocate twice as much and start the stack in the middle.
     */
    if ((c->clone_stack = malloc(2 * START_CHILD_CLONE_STACK_SIZE)) == NULL)
        /* errno will be set to ENOMEM */
        return -1;
    return clone(childProcess,
                 c->clone_stack + START_CHILD_CLONE_STACK_SIZE,
                 CLONE_VFORK | CLONE_VM | SIGCHLD, c);
#else
  #if START_CHILD_USE_VFORK
    /*
     * We separate the call to vfork into a separate function to make
     * very sure to keep stack of child from corrupting stack of parent,
     * as suggested by the scary gcc warning:
     *  warning: variable 'foo' might be clobbered by 'longjmp' or 'vfork'
     */
    volatile pid_t resultPid = vfork();
  #else
    /*
     * From Solaris fork(2): In Solaris 10, a call to fork() is
     * identical to a call to fork1(); only the calling thread is
     * replicated in the child process. This is the POSIX-specified
     * behavior for fork().
     */
    pid_t resultPid = fork();
  #endif
    if (resultPid == 0)
        childProcess(c);
    assert(resultPid != 0);  /* childProcess never returns */
    return resultPid;
#endif /* ! START_CHILD_USE_CLONE */
}

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JNIEXPORT jint JNICALL
Java_java_lang_UNIXProcess_forkAndExec(JNIEnv *env,
                                       jobject process,
                                       jbyteArray prog,
                                       jbyteArray argBlock, jint argc,
                                       jbyteArray envBlock, jint envc,
                                       jbyteArray dir,
817 818
                                       jintArray std_fds,
                                       jboolean redirectErrorStream)
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{
    int errnum;
    int resultPid = -1;
    int in[2], out[2], err[2], fail[2];
823
    jint *fds = NULL;
824 825 826 827
    const char *pprog = NULL;
    const char *pargBlock = NULL;
    const char *penvBlock = NULL;
    ChildStuff *c;
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    in[0] = in[1] = out[0] = out[1] = err[0] = err[1] = fail[0] = fail[1] = -1;

831 832 833 834
    if ((c = NEW(ChildStuff, 1)) == NULL) return -1;
    c->argv = NULL;
    c->envv = NULL;
    c->pdir = NULL;
835 836 837
#if START_CHILD_USE_CLONE
    c->clone_stack = NULL;
#endif
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839 840 841 842 843 844 845 846 847 848
    /* Convert prog + argBlock into a char ** argv.
     * Add one word room for expansion of argv for use by
     * execve_as_traditional_shell_script.
     */
    assert(prog != NULL && argBlock != NULL);
    if ((pprog     = getBytes(env, prog))       == NULL) goto Catch;
    if ((pargBlock = getBytes(env, argBlock))   == NULL) goto Catch;
    if ((c->argv = NEW(const char *, argc + 3)) == NULL) goto Catch;
    c->argv[0] = pprog;
    initVectorFromBlock(c->argv+1, pargBlock, argc);
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    if (envBlock != NULL) {
851 852 853 854 855 856 857 858
        /* Convert envBlock into a char ** envv */
        if ((penvBlock = getBytes(env, envBlock))   == NULL) goto Catch;
        if ((c->envv = NEW(const char *, envc + 1)) == NULL) goto Catch;
        initVectorFromBlock(c->envv, penvBlock, envc);
    }

    if (dir != NULL) {
        if ((c->pdir = getBytes(env, dir)) == NULL) goto Catch;
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    }

861 862 863 864 865 866 867
    assert(std_fds != NULL);
    fds = (*env)->GetIntArrayElements(env, std_fds, NULL);
    if (fds == NULL) goto Catch;

    if ((fds[0] == -1 && pipe(in)  < 0) ||
        (fds[1] == -1 && pipe(out) < 0) ||
        (fds[2] == -1 && pipe(err) < 0) ||
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868 869 870 871
        (pipe(fail) < 0)) {
        throwIOException(env, errno, "Bad file descriptor");
        goto Catch;
    }
872 873 874 875 876 877 878 879 880 881 882
    c->fds[0] = fds[0];
    c->fds[1] = fds[1];
    c->fds[2] = fds[2];

    copyPipe(in,   c->in);
    copyPipe(out,  c->out);
    copyPipe(err,  c->err);
    copyPipe(fail, c->fail);

    c->redirectErrorStream = redirectErrorStream;

883 884
    resultPid = startChild(c);
    assert(resultPid != 0);
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    if (resultPid < 0) {
887
        throwIOException(env, errno, START_CHILD_SYSTEM_CALL " failed");
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        goto Catch;
    }

891
    restartableClose(fail[1]); fail[1] = -1; /* See: WhyCantJohnnyExec */
892 893 894 895

    switch (readFully(fail[0], &errnum, sizeof(errnum))) {
    case 0: break; /* Exec succeeded */
    case sizeof(errnum):
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        waitpid(resultPid, NULL, 0);
        throwIOException(env, errnum, "Exec failed");
        goto Catch;
899 900 901
    default:
        throwIOException(env, errno, "Read failed");
        goto Catch;
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902 903
    }

904 905 906
    fds[0] = (in [1] != -1) ? in [1] : -1;
    fds[1] = (out[0] != -1) ? out[0] : -1;
    fds[2] = (err[0] != -1) ? err[0] : -1;
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907 908

 Finally:
909 910
#if START_CHILD_USE_CLONE
    free(c->clone_stack);
911 912
#endif

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913 914 915 916 917 918 919 920 921 922 923 924
    /* Always clean up the child's side of the pipes */
    closeSafely(in [0]);
    closeSafely(out[1]);
    closeSafely(err[1]);

    /* Always clean up fail descriptors */
    closeSafely(fail[0]);
    closeSafely(fail[1]);

    releaseBytes(env, prog,     pprog);
    releaseBytes(env, argBlock, pargBlock);
    releaseBytes(env, envBlock, penvBlock);
925 926 927 928 929
    releaseBytes(env, dir,      c->pdir);

    free(c->argv);
    free(c->envv);
    free(c);
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931 932 933
    if (fds != NULL)
        (*env)->ReleaseIntArrayElements(env, std_fds, fds, 0);

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    return resultPid;

 Catch:
    /* Clean up the parent's side of the pipes in case of failure only */
    closeSafely(in [1]);
    closeSafely(out[0]);
    closeSafely(err[0]);
    goto Finally;
}

JNIEXPORT void JNICALL
Java_java_lang_UNIXProcess_destroyProcess(JNIEnv *env, jobject junk, jint pid)
{
    kill(pid, SIGTERM);
}