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helper.c

/*
 * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
 * Licensed under the GPL
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <limits.h>
#include <sys/signal.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include "user.h"
#include "kern_util.h"
#include "os.h"
#include "um_malloc.h"
#include "kern_constants.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 errval;

      if (data->pre_exec != NULL)
            (*data->pre_exec)(data->pre_data);
      errval = execvp_noalloc(data->buf, argv[0], argv);
      printk("helper_child - execvp of '%s' failed - errno = %d\n", argv[0],
             -errval);
      write(data->fd, &errval, sizeof(errval));
      kill(os_getpid(), SIGKILL);
      return 0;
}

/* Returns either the pid of the child process we run or -E* on failure.
 * XXX The alloc_stack here breaks if this is called in the tracing thread, so
 * we need to receive a preallocated stack (a local buffer is ok). */
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("run_helper : pipe failed, errno = %d\n", errno);
            goto out_free;
      }

      ret = os_set_exec_close(fds[1]);
      if (ret < 0) {
            printk("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() ? kmalloc(PATH_MAX, UM_GFP_ATOMIC) :
                              kmalloc(PATH_MAX, UM_GFP_KERNEL);
      pid = clone(helper_child, (void *) sp, CLONE_VM, &data);
      if (pid < 0) {
            ret = -errno;
            printk("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("run_helper : read on pipe failed, ret = %d\n",
                         -n);
                  ret = n;
                  kill(pid, SIGKILL);
            }
            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("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("run_helper_thread - wait failed, errno = %d\n",
                         errno);
                  pid = err;
            }
            if (!WIFEXITED(status) || (WEXITSTATUS(status) != 0))
                  printk("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 nohang, char *pname)
{
      int ret, status;
      int wflags = __WCLONE;

      if (nohang)
            wflags |= WNOHANG;

      if (!pname)
            pname = "helper_wait";

      CATCH_EINTR(ret = waitpid(pid, &status, wflags));
      if (ret < 0) {
            printk(UM_KERN_ERR "%s : waitpid process %d failed, "
                   "errno = %d\n", pname, pid, errno);
            return -errno;
      } else if (nohang && ret == 0) {
            printk(UM_KERN_ERR "%s : process %d has not exited\n",
                   pname, pid);
            return -ECHILD;
      } else if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
            printk(UM_KERN_ERR "%s : process %d didn't exit with "
                   "status 0\n", pname, pid);
            return -ECHILD;
      } else
            return 0;
}

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