helper.c

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/*
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <linux/limits.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <kern_util.h>
#include <os.h>
#include <um_malloc.h>

struct helper_data {
    void (*pre_exec)(void*);
    void *pre_data;
    char **argv;
    int fd;
    char *buf;
};

static int helper_child(void *arg)
{
    struct helper_data *data = arg;
    char **argv = data->argv;
    int err, ret;

    if (data->pre_exec != NULL)
        (*data->pre_exec)(data->pre_data);
    err = execvp_noalloc(data->buf, argv[0], argv);

    /* If the exec succeeds, we don't get here */
    CATCH_EINTR(ret = write(data->fd, &err, sizeof(err)));

    return 0;
}

/* Returns either the pid of the child process we run or -E* on failure. */
int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
{
    struct helper_data data;
    unsigned long stack, sp;
    int pid, fds[2], ret, n;

    stack = alloc_stack(0, __cant_sleep());
    if (stack == 0)
        return -ENOMEM;

    ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
    if (ret < 0) {
        ret = -errno;
        printk(UM_KERN_ERR "run_helper : pipe failed, errno = %d\n",
               errno);
        goto out_free;
    }

    ret = os_set_exec_close(fds[1]);
    if (ret < 0) {
        printk(UM_KERN_ERR "run_helper : setting FD_CLOEXEC failed, "
               "ret = %d\n", -ret);
        goto out_close;
    }

    sp = stack + UM_KERN_PAGE_SIZE - sizeof(void *);
    data.pre_exec = pre_exec;
    data.pre_data = pre_data;
    data.argv = argv;
    data.fd = fds[1];
    data.buf = __cant_sleep() ? uml_kmalloc(PATH_MAX, UM_GFP_ATOMIC) :
                    uml_kmalloc(PATH_MAX, UM_GFP_KERNEL);
    pid = clone(helper_child, (void *) sp, CLONE_VM, &data);
    if (pid < 0) {
        ret = -errno;
        printk(UM_KERN_ERR "run_helper : clone failed, errno = %d\n",
               errno);
        goto out_free2;
    }

    close(fds[1]);
    fds[1] = -1;

    /*
     * Read the errno value from the child, if the exec failed, or get 0 if
     * the exec succeeded because the pipe fd was set as close-on-exec.
     */
    n = read(fds[0], &ret, sizeof(ret));
    if (n == 0) {
        ret = pid;
    } else {
        if (n < 0) {
            n = -errno;
            printk(UM_KERN_ERR "run_helper : read on pipe failed, "
                   "ret = %d\n", -n);
            ret = n;
        }
        CATCH_EINTR(waitpid(pid, NULL, __WCLONE));
    }

out_free2:
    kfree(data.buf);
out_close:
    if (fds[1] != -1)
        close(fds[1]);
    close(fds[0]);
out_free:
    free_stack(stack, 0);
    return ret;
}

int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
              unsigned long *stack_out)
{
    unsigned long stack, sp;
    int pid, status, err;

    stack = alloc_stack(0, __cant_sleep());
    if (stack == 0)
        return -ENOMEM;

    sp = stack + UM_KERN_PAGE_SIZE - sizeof(void *);
    pid = clone(proc, (void *) sp, flags, arg);
    if (pid < 0) {
        err = -errno;
        printk(UM_KERN_ERR "run_helper_thread : clone failed, "
               "errno = %d\n", errno);
        return err;
    }
    if (stack_out == NULL) {
        CATCH_EINTR(pid = waitpid(pid, &status, __WCLONE));
        if (pid < 0) {
            err = -errno;
            printk(UM_KERN_ERR "run_helper_thread - wait failed, "
                   "errno = %d\n", errno);
            pid = err;
        }
        if (!WIFEXITED(status) || (WEXITSTATUS(status) != 0))
            printk(UM_KERN_ERR "run_helper_thread - thread "
                   "returned status 0x%x\n", status);
        free_stack(stack, 0);
    } else
        *stack_out = stack;
    return pid;
}

int helper_wait(int pid)
{
    int ret, status;
    int wflags = __WCLONE;

    CATCH_EINTR(ret = waitpid(pid, &status, wflags));
    if (ret < 0) {
        printk(UM_KERN_ERR "helper_wait : waitpid process %d failed, "
               "errno = %d\n", pid, errno);
        return -errno;
    } else if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        printk(UM_KERN_ERR "helper_wait : process %d exited with "
               "status 0x%x\n", pid, status);
        return -ECHILD;
    } else
        return 0;
}