port/threads/spawn.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2011 by Delphix. All rights reserved.
 */

#include "lint.h"
#include "thr_uberdata.h"
#include <sys/libc_kernel.h>
#include <sys/procset.h>
#include <sys/fork.h>
#include <dirent.h>
#include <alloca.h>
#include <spawn.h>
#include <paths.h>

#define ALL_POSIX_SPAWN_FLAGS           \
        (POSIX_SPAWN_RESETIDS |     \
        POSIX_SPAWN_SETPGROUP |     \
        POSIX_SPAWN_SETSIGDEF |     \
        POSIX_SPAWN_SETSIGMASK |    \
        POSIX_SPAWN_SETSCHEDPARAM | \
        POSIX_SPAWN_SETSCHEDULER |  \
        POSIX_SPAWN_SETSIGIGN_NP |  \
        POSIX_SPAWN_NOSIGCHLD_NP |  \
        POSIX_SPAWN_WAITPID_NP |    \
        POSIX_SPAWN_NOEXECERR_NP)

typedef struct {
    int     sa_psflags; /* POSIX_SPAWN_* flags */
    int     sa_priority;
    int     sa_schedpolicy;
    pid_t       sa_pgroup;
    sigset_t    sa_sigdefault;
    sigset_t    sa_sigignore;
    sigset_t    sa_sigmask;
} spawn_attr_t;

typedef struct file_attr {
    struct file_attr *fa_next;  /* circular list of file actions */
    struct file_attr *fa_prev;
    enum {FA_OPEN, FA_CLOSE, FA_DUP2, FA_CLOSEFROM} fa_type;
    int     fa_need_dirbuf; /* only consulted in the head action */
    char        *fa_path;   /* copied pathname for open() */
    uint_t      fa_pathsize;    /* size of fa_path[] array */
    int     fa_oflag;   /* oflag for open() */
    mode_t      fa_mode;    /* mode for open() */
    int     fa_filedes; /* file descriptor for open()/close() */
    int     fa_newfiledes;  /* new file descriptor for dup2() */
} file_attr_t;

#if defined(_LP64)
#define __open64    __open
#define getdents64  getdents
#define dirent64_t  dirent_t
#else
extern int getdents64(int, dirent64_t *, size_t);
#endif

extern const char **_environ;

/*
 * Support function:
 * Close all open file descriptors greater than or equal to lowfd.
 * This is executed in the child of vfork(), so we must not call
 * opendir() / readdir() because that would alter the parent's
 * address space.  We use the low-level getdents64() system call.
 * Return non-zero on error.
 */
static int
spawn_closefrom(int lowfd, void *buf)
{
    int procfd;
    int fd;
    int buflen;
    dirent64_t *dp;
    dirent64_t *dpend;

    if (lowfd <  0)
        lowfd = 0;

    /*
     * Close lowfd right away as a hedge against failing
     * to open the /proc file descriptor directory due
     * all file descriptors being currently used up.
     */
    (void) __close(lowfd++);

    if ((procfd = __open64("/proc/self/fd", O_RDONLY, 0)) < 0) {
        /*
         * We could not open the /proc file descriptor directory.
         * Just fail and be done with it.
         */
        return (-1);
    }

    for (;;) {
        /*
         * Collect a bunch of open file descriptors and close them.
         * Repeat until the directory is exhausted.
         */
        dp = (dirent64_t *)buf;
        if ((buflen = getdents64(procfd, dp, DIRBUF)) <= 0) {
            (void) __close(procfd);
            break;
        }
        dpend = (dirent64_t *)((uintptr_t)buf + buflen);
        do {
            /* skip '.', '..' and procfd */
            if (dp->d_name[0] != '.' &&
                (fd = atoi(dp->d_name)) != procfd &&
                fd >= lowfd)
                (void) __close(fd);
            dp = (dirent64_t *)((uintptr_t)dp + dp->d_reclen);
        } while (dp < dpend);
    }

    return (0);
}

static int
perform_flag_actions(spawn_attr_t *sap)
{
    int sig;
    struct sigaction action;

    if (sap->sa_psflags & POSIX_SPAWN_SETSIGMASK) {
        (void) __lwp_sigmask(SIG_SETMASK, &sap->sa_sigmask);
    }

    if (sap->sa_psflags & POSIX_SPAWN_SETSIGIGN_NP) {
        (void) memset(&action, 0, sizeof (action));
        action.sa_handler = SIG_IGN;
        for (sig = 1; sig < NSIG; sig++) {
            if (sigismember(&sap->sa_sigignore, sig))
                (void) __sigaction(sig, &action, NULL);
        }
    }

    if (sap->sa_psflags & POSIX_SPAWN_SETSIGDEF) {
        (void) memset(&action, 0, sizeof (action));
        action.sa_handler = SIG_DFL;
        for (sig = 1; sig < NSIG; sig++) {
            if (sigismember(&sap->sa_sigdefault, sig))
                (void) __sigaction(sig, &action, NULL);
        }
    }

    if (sap->sa_psflags & POSIX_SPAWN_RESETIDS) {
        if (setgid(getgid()) != 0 || setuid(getuid()) != 0)
            return (errno);
    }

    if (sap->sa_psflags & POSIX_SPAWN_SETPGROUP) {
        if (setpgid(0, sap->sa_pgroup) != 0)
            return (errno);
    }

    if (sap->sa_psflags & POSIX_SPAWN_SETSCHEDULER) {
        if (setparam(P_LWPID, P_MYID,
            sap->sa_schedpolicy, sap->sa_priority) == -1)
            return (errno);
    } else if (sap->sa_psflags & POSIX_SPAWN_SETSCHEDPARAM) {
        if (setprio(P_LWPID, P_MYID, sap->sa_priority, NULL) == -1)
            return (errno);
    }

    return (0);
}

static int
perform_file_actions(file_attr_t *fap, void *dirbuf)
{
    file_attr_t *froot = fap;
    int fd;

    do {
        switch (fap->fa_type) {
        case FA_OPEN:
            fd = __open(fap->fa_path, fap->fa_oflag, fap->fa_mode);
            if (fd < 0)
                return (errno);
            if (fd != fap->fa_filedes) {
                if (__fcntl(fd, F_DUP2FD, fap->fa_filedes) < 0)
                    return (errno);
                (void) __close(fd);
            }
            break;
        case FA_CLOSE:
            if (__close(fap->fa_filedes) == -1 &&
                errno != EBADF) /* already closed, no error */
                return (errno);
            break;
        case FA_DUP2:
            fd = __fcntl(fap->fa_filedes, F_DUP2FD,
                fap->fa_newfiledes);
            if (fd < 0)
                return (errno);
            break;
        case FA_CLOSEFROM:
            if (spawn_closefrom(fap->fa_filedes, dirbuf))
                return (errno);
            break;
        }
    } while ((fap = fap->fa_next) != froot);

    return (0);
}

static int
forkflags(spawn_attr_t *sap)
{
    int flags = 0;

    if (sap != NULL) {
        if (sap->sa_psflags & POSIX_SPAWN_NOSIGCHLD_NP)
            flags |= FORK_NOSIGCHLD;
        if (sap->sa_psflags & POSIX_SPAWN_WAITPID_NP)
            flags |= FORK_WAITPID;
    }

    return (flags);
}

/*
 * set_error() / get_error() are used to guarantee that the local variable
 * 'error' is set correctly in memory on return from vfork() in the parent.
 */

static int
set_error(int *errp, int err)
{
    return (*errp = err);
}

static int
get_error(int *errp)
{
    return (*errp);
}

/*
 * For MT safety, do not invoke the dynamic linker after calling vfork().
 * If some other thread was in the dynamic linker when this thread's parent
 * called vfork() then the dynamic linker's lock would still be held here
 * (with a defunct owner) and we would deadlock ourself if we invoked it.
 *
 * Therefore, all of the functions we call here after returning from
 * vforkx() in the child are not and must never be exported from libc
 * as global symbols.  To do so would risk invoking the dynamic linker.
 */

int
posix_spawn(
    pid_t *pidp,
    const char *path,
    const posix_spawn_file_actions_t *file_actions,
    const posix_spawnattr_t *attrp,
    char *const *argv,
    char *const *envp)
{
    spawn_attr_t *sap = attrp? attrp->__spawn_attrp : NULL;
    file_attr_t *fap = file_actions? file_actions->__file_attrp : NULL;
    void *dirbuf = NULL;
    int error;      /* this will be set by the child */
    pid_t pid;

    if (attrp != NULL && sap == NULL)
        return (EINVAL);

    if (fap != NULL && fap->fa_need_dirbuf) {
        /*
         * Preallocate the buffer for the call to getdents64() in
         * spawn_closefrom() since we can't do it in the vfork() child.
         */
        if ((dirbuf = lmalloc(DIRBUF)) == NULL)
            return (ENOMEM);
    }

    switch (pid = vforkx(forkflags(sap))) {
    case 0:         /* child */
        break;
    case -1:        /* parent, failure */
        if (dirbuf)
            lfree(dirbuf, DIRBUF);
        return (errno);
    default:        /* parent, success */
        /*
         * We don't get here until the child exec()s or exit()s
         */
        if (pidp != NULL && get_error(&error) == 0)
            *pidp = pid;
        if (dirbuf)
            lfree(dirbuf, DIRBUF);
        return (get_error(&error));
    }

    if (sap != NULL)
        if (set_error(&error, perform_flag_actions(sap)) != 0)
            _exit(_EVAPORATE);

    if (fap != NULL)
        if (set_error(&error, perform_file_actions(fap, dirbuf)) != 0)
            _exit(_EVAPORATE);

    (void) set_error(&error, 0);
    (void) execve(path, argv, envp);
    if (sap != NULL && (sap->sa_psflags & POSIX_SPAWN_NOEXECERR_NP))
        _exit(127);
    (void) set_error(&error, errno);
    _exit(_EVAPORATE);
    return (0); /* not reached */
}

/*
 * Much of posix_spawnp() blatently stolen from execvp() (port/gen/execvp.c).
 */

extern int libc__xpg4;

static const char *
execat(const char *s1, const char *s2, char *si)
{
    int cnt = PATH_MAX + 1;
    char *s;
    char c;

    for (s = si; (c = *s1) != '\0' && c != ':'; s1++) {
        if (cnt > 0) {
            *s++ = c;
            cnt--;
        }
    }
    if (si != s && cnt > 0) {
        *s++ = '/';
        cnt--;
    }
    for (; (c = *s2) != '\0' && cnt > 0; s2++) {
        *s++ = c;
        cnt--;
    }
    *s = '\0';
    return (*s1? ++s1: NULL);
}

/* ARGSUSED */
int
posix_spawnp(
    pid_t *pidp,
    const char *file,
    const posix_spawn_file_actions_t *file_actions,
    const posix_spawnattr_t *attrp,
    char *const *argv,
    char *const *envp)
{
    spawn_attr_t *sap = attrp? attrp->__spawn_attrp : NULL;
    file_attr_t *fap = file_actions? file_actions->__file_attrp : NULL;
    void *dirbuf = NULL;
    const char *pathstr = (strchr(file, '/') == NULL)? getenv("PATH") : "";
    int xpg4 = libc__xpg4;
    int error = 0;      /* this will be set by the child */
    char path[PATH_MAX+4];
    const char *cp;
    pid_t pid;
    char **newargs;
    int argc;
    int i;

    if (attrp != NULL && sap == NULL)
        return (EINVAL);

    if (*file == '\0')
        return (EACCES);

    if (fap != NULL && fap->fa_need_dirbuf) {
        /*
         * Preallocate the buffer for the call to getdents64() in
         * spawn_closefrom() since we can't do it in the vfork() child.
         */
        if ((dirbuf = lmalloc(DIRBUF)) == NULL)
            return (ENOMEM);
    }

    /*
     * We may need to invoke the shell with a slightly modified
     * argv[] array.  To do this we need to preallocate the array.
     * We must call alloca() before calling vfork() because doing
     * it after vfork() (in the child) would corrupt the parent.
     */
    for (argc = 0; argv[argc] != NULL; argc++)
        continue;
    newargs = alloca((argc + 2) * sizeof (char *));

    switch (pid = vforkx(forkflags(sap))) {
    case 0:         /* child */
        break;
    case -1:        /* parent, failure */
        if (dirbuf)
            lfree(dirbuf, DIRBUF);
        return (errno);
    default:        /* parent, success */
        /*
         * We don't get here until the child exec()s or exit()s
         */
        if (pidp != NULL && get_error(&error) == 0)
            *pidp = pid;
        if (dirbuf)
            lfree(dirbuf, DIRBUF);
        return (get_error(&error));
    }

    if (sap != NULL)
        if (set_error(&error, perform_flag_actions(sap)) != 0)
            _exit(_EVAPORATE);

    if (fap != NULL)
        if (set_error(&error, perform_file_actions(fap, dirbuf)) != 0)
            _exit(_EVAPORATE);

    if (pathstr == NULL) {
        /*
         * XPG4:  pathstr is equivalent to _CS_PATH, except that
         * :/usr/sbin is appended when root, and pathstr must end
         * with a colon when not root.  Keep these paths in sync
         * with _CS_PATH in confstr.c.  Note that pathstr must end
         * with a colon when not root so that when file doesn't
         * contain '/', the last call to execat() will result in an
         * attempt to execv file from the current directory.
         */
        if (geteuid() == 0 || getuid() == 0) {
            if (!xpg4)
                pathstr = "/usr/sbin:/usr/ccs/bin:/usr/bin";
            else
                pathstr = "/usr/xpg4/bin:/usr/ccs/bin:"
                    "/usr/bin:/opt/SUNWspro/bin:/usr/sbin";
        } else {
            if (!xpg4)
                pathstr = "/usr/ccs/bin:/usr/bin:";
            else
                pathstr = "/usr/xpg4/bin:/usr/ccs/bin:"
                    "/usr/bin:/opt/SUNWspro/bin:";
        }
    }

    cp = pathstr;
    do {
        cp = execat(cp, file, path);
        /*
         * 4025035 and 4038378
         * if a filename begins with a "-" prepend "./" so that
         * the shell can't interpret it as an option
         */
        if (*path == '-') {
            char *s;

            for (s = path; *s != '\0'; s++)
                continue;
            for (; s >= path; s--)
                *(s + 2) = *s;
            path[0] = '.';
            path[1] = '/';
        }
        (void) set_error(&error, 0);
        (void) execve(path, argv, envp);
        if (set_error(&error, errno) == ENOEXEC) {
            newargs[0] = "sh";
            newargs[1] = path;
            for (i = 1; i <= argc; i++)
                newargs[i + 1] = argv[i];
            (void) set_error(&error, 0);
            (void) execve(_PATH_BSHELL, newargs, envp);
            if (sap != NULL &&
                (sap->sa_psflags & POSIX_SPAWN_NOEXECERR_NP))
                _exit(127);
            (void) set_error(&error, errno);
            _exit(_EVAPORATE);
        }
    } while (cp);

    if (sap != NULL &&
        (sap->sa_psflags & POSIX_SPAWN_NOEXECERR_NP)) {
        (void) set_error(&error, 0);
        _exit(127);
    }
    _exit(_EVAPORATE);
    return (0); /* not reached */
}

int
posix_spawn_file_actions_init(
    posix_spawn_file_actions_t *file_actions)
{
    file_actions->__file_attrp = NULL;
    return (0);
}

int
posix_spawn_file_actions_destroy(
    posix_spawn_file_actions_t *file_actions)
{
    file_attr_t *froot = file_actions->__file_attrp;
    file_attr_t *fap;
    file_attr_t *next;

    if ((fap = froot) != NULL) {
        do {
            next = fap->fa_next;
            if (fap->fa_type == FA_OPEN)
                lfree(fap->fa_path, fap->fa_pathsize);
            lfree(fap, sizeof (*fap));
        } while ((fap = next) != froot);
    }
    file_actions->__file_attrp = NULL;
    return (0);
}

static void
add_file_attr(posix_spawn_file_actions_t *file_actions, file_attr_t *fap)
{
    file_attr_t *froot = file_actions->__file_attrp;

    if (froot == NULL) {
        fap->fa_next = fap->fa_prev = fap;
        file_actions->__file_attrp = froot = fap;
    } else {
        fap->fa_next = froot;
        fap->fa_prev = froot->fa_prev;
        froot->fa_prev->fa_next = fap;
        froot->fa_prev = fap;
    }

    /*
     * Once set, __file_attrp no longer changes, so this assignment
     * always goes into the first element in the list, as required.
     */
    if (fap->fa_type == FA_CLOSEFROM)
        froot->fa_need_dirbuf = 1;
}

int
posix_spawn_file_actions_addopen(
    posix_spawn_file_actions_t *file_actions,
    int filedes,
    const char *path,
    int oflag,
    mode_t mode)
{
    file_attr_t *fap;

    if (filedes < 0)
        return (EBADF);
    if ((fap = lmalloc(sizeof (*fap))) == NULL)
        return (ENOMEM);

    fap->fa_pathsize = strlen(path) + 1;
    if ((fap->fa_path = lmalloc(fap->fa_pathsize)) == NULL) {
        lfree(fap, sizeof (*fap));
        return (ENOMEM);
    }
    (void) strcpy(fap->fa_path, path);

    fap->fa_type = FA_OPEN;
    fap->fa_oflag = oflag;
    fap->fa_mode = mode;
    fap->fa_filedes = filedes;
    add_file_attr(file_actions, fap);

    return (0);
}

int
posix_spawn_file_actions_addclose(
    posix_spawn_file_actions_t *file_actions,
    int filedes)
{
    file_attr_t *fap;

    if (filedes < 0)
        return (EBADF);
    if ((fap = lmalloc(sizeof (*fap))) == NULL)
        return (ENOMEM);

    fap->fa_type = FA_CLOSE;
    fap->fa_filedes = filedes;
    add_file_attr(file_actions, fap);

    return (0);
}

int
posix_spawn_file_actions_adddup2(
    posix_spawn_file_actions_t *file_actions,
    int filedes,
    int newfiledes)
{
    file_attr_t *fap;

    if (filedes < 0 || newfiledes < 0)
        return (EBADF);
    if ((fap = lmalloc(sizeof (*fap))) == NULL)
        return (ENOMEM);

    fap->fa_type = FA_DUP2;
    fap->fa_filedes = filedes;
    fap->fa_newfiledes = newfiledes;
    add_file_attr(file_actions, fap);

    return (0);
}

int
posix_spawn_file_actions_addclosefrom_np(
    posix_spawn_file_actions_t *file_actions,
    int lowfiledes)
{
    file_attr_t *fap;

    if (lowfiledes < 0)
        return (EBADF);
    if ((fap = lmalloc(sizeof (*fap))) == NULL)
        return (ENOMEM);
    fap->fa_type = FA_CLOSEFROM;
    fap->fa_filedes = lowfiledes;
    add_file_attr(file_actions, fap);

    return (0);
}

int
posix_spawnattr_init(
    posix_spawnattr_t *attr)
{
    if ((attr->__spawn_attrp = lmalloc(sizeof (posix_spawnattr_t))) == NULL)
        return (ENOMEM);
    /*
     * Add default stuff here?
     */
    return (0);
}

int
posix_spawnattr_destroy(
    posix_spawnattr_t *attr)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    /*
     * deallocate stuff here?
     */
    lfree(sap, sizeof (*sap));
    attr->__spawn_attrp = NULL;
    return (0);
}

int
posix_spawnattr_setflags(
    posix_spawnattr_t *attr,
    short flags)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL ||
        (flags & ~ALL_POSIX_SPAWN_FLAGS))
        return (EINVAL);

    sap->sa_psflags = flags;
    return (0);
}

int
posix_spawnattr_getflags(
    const posix_spawnattr_t *attr,
    short *flags)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *flags = sap->sa_psflags;
    return (0);
}

int
posix_spawnattr_setpgroup(
    posix_spawnattr_t *attr,
    pid_t pgroup)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    sap->sa_pgroup = pgroup;
    return (0);
}

int
posix_spawnattr_getpgroup(
    const posix_spawnattr_t *attr,
    pid_t *pgroup)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *pgroup = sap->sa_pgroup;
    return (0);
}

int
posix_spawnattr_setschedparam(
    posix_spawnattr_t *attr,
    const struct sched_param *schedparam)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    /*
     * Check validity?
     */
    sap->sa_priority = schedparam->sched_priority;
    return (0);
}

int
posix_spawnattr_getschedparam(
    const posix_spawnattr_t *attr,
    struct sched_param *schedparam)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    schedparam->sched_priority = sap->sa_priority;
    return (0);
}

int
posix_spawnattr_setschedpolicy(
    posix_spawnattr_t *attr,
    int schedpolicy)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL || schedpolicy == SCHED_SYS)
        return (EINVAL);

    /*
     * Cache the policy information for later use
     * by the vfork() child of posix_spawn().
     */
    if (get_info_by_policy(schedpolicy) == NULL)
        return (errno);

    sap->sa_schedpolicy = schedpolicy;
    return (0);
}

int
posix_spawnattr_getschedpolicy(
    const posix_spawnattr_t *attr,
    int *schedpolicy)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *schedpolicy = sap->sa_schedpolicy;
    return (0);
}

int
posix_spawnattr_setsigdefault(
    posix_spawnattr_t *attr,
    const sigset_t *sigdefault)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    sap->sa_sigdefault = *sigdefault;
    return (0);
}

int
posix_spawnattr_getsigdefault(
    const posix_spawnattr_t *attr,
    sigset_t *sigdefault)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *sigdefault = sap->sa_sigdefault;
    return (0);
}

int
posix_spawnattr_setsigignore_np(
    posix_spawnattr_t *attr,
    const sigset_t *sigignore)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    sap->sa_sigignore = *sigignore;
    return (0);
}

int
posix_spawnattr_getsigignore_np(
    const posix_spawnattr_t *attr,
    sigset_t *sigignore)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *sigignore = sap->sa_sigignore;
    return (0);
}

int
posix_spawnattr_setsigmask(
    posix_spawnattr_t *attr,
    const sigset_t *sigmask)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    sap->sa_sigmask = *sigmask;
    return (0);
}

int
posix_spawnattr_getsigmask(
    const posix_spawnattr_t *attr,
    sigset_t *sigmask)
{
    spawn_attr_t *sap = attr->__spawn_attrp;

    if (sap == NULL)
        return (EINVAL);

    *sigmask = sap->sa_sigmask;
    return (0);
}

/*
 * Spawn a process to run "sh -c <cmd>".  Return the child's pid (in
 * *pidp), and a file descriptor (in *fdp) for reading or writing to the
 * child process, depending on the 'write' argument.
 * Return 0 on success; otherwise return an error code.
 */
int
posix_spawn_pipe_np(pid_t *pidp, int *fdp,
    const char *cmd, boolean_t write,
    posix_spawn_file_actions_t *fact, posix_spawnattr_t *attr)
{
    int p[2];
    int myside, yourside, stdio;
    const char *shpath = _PATH_BSHELL;
    const char *argvec[4] = { "sh", "-c", cmd, NULL };
    int error;

    if (pipe(p) < 0)
        return (errno);

    if (access(shpath, X_OK))   /* XPG4 Requirement: */
        shpath = "";        /* force child to fail immediately */

    if (write) {
        /*
         * Data is read from p[0] and written to p[1].
         * 'stdio' is the fd in the child process that should be
         * connected to the pipe.
         */
        myside = p[1];
        yourside = p[0];
        stdio = STDIN_FILENO;
    } else {
        myside = p[0];
        yourside = p[1];
        stdio = STDOUT_FILENO;
    }

    error = posix_spawn_file_actions_addclose(fact, myside);
    if (yourside != stdio) {
        if (error == 0) {
            error = posix_spawn_file_actions_adddup2(fact,
                yourside, stdio);
        }
        if (error == 0) {
            error = posix_spawn_file_actions_addclose(fact,
                yourside);
        }
    }

    if (error)
        return (error);
    error = posix_spawn(pidp, shpath, fact, attr,
        (char *const *)argvec, (char *const *)_environ);
    (void) close(yourside);
    if (error) {
        (void) close(myside);
        return (error);
    }

    *fdp = myside;
    return (0);
}