xen/tools/libxl/libxl_exec.c

/*
 * Copyright (C) 2009      Citrix Ltd.
 * Author Vincent Hanquez <vincent.hanquez@eu.citrix.com>
 * Author Stefano Stabellini <stefano.stabellini@eu.citrix.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; version 2.1 only. with the special
 * exception on linking described in file LICENSE.
 *
 * This program 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 Lesser General Public License for more details.
 */

#include "libxl_osdeps.h"

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h> /* for SIGKILL */
#include <fcntl.h>

#include "libxl.h"
#include "libxl_internal.h"

static int call_waitpid(pid_t (*waitpid_cb)(pid_t, int *, int), pid_t pid, int *status, int options)
{
    return (waitpid_cb) ? waitpid_cb(pid, status, options) : waitpid(pid, status, options);
}

static void check_open_fds(const char *what)
{
    const char *env_debug;
    int debug;
    int i, flags, badness = 0;

    env_debug = getenv("_LIBXL_DEBUG_EXEC_FDS");
    if (!env_debug) return;

    debug = strtol(env_debug, (char **) NULL, 10);
    if (debug <= 0) return;

    for (i = 4; i < 256; i++) {
#ifdef __linux__
        size_t len;
        char path[PATH_MAX];
        char link[PATH_MAX+1];
#endif
        flags = fcntl(i, F_GETFD);
        if ( flags == -1 ) {
            if ( errno != EBADF )
                fprintf(stderr, "libxl: execing %s: fd %d flags returned %s (%d)\n",
                        what, i, strerror(errno), errno);
            continue;
        }

        if ( flags & FD_CLOEXEC )
            continue;

        badness++;

#ifdef __linux__
        snprintf(path, PATH_MAX, "/proc/%d/fd/%d", getpid(), i);
        len = readlink(path, link, PATH_MAX);
        if (len > 0) {
            link[len] = '\0';
            fprintf(stderr, "libxl: execing %s: fd %d is open to %s with flags %#x\n",
                    what, i, link, flags);
        } else
#endif
            fprintf(stderr, "libxl: execing %s: fd %d is open with flags %#x\n",
                    what, i, flags);
    }
    if (debug < 2) return;
    if (badness) abort();
}

void libxl__exec(int stdinfd, int stdoutfd, int stderrfd, const char *arg0,
                char **args)
     /* call this in the child */
{
    if (stdinfd != -1)
        dup2(stdinfd, STDIN_FILENO);
    if (stdoutfd != -1)
        dup2(stdoutfd, STDOUT_FILENO);
    if (stderrfd != -1)
        dup2(stderrfd, STDERR_FILENO);

    if (stdinfd != -1)
        close(stdinfd);
    if (stdoutfd != -1 && stdoutfd != stdinfd)
        close(stdoutfd);
    if (stderrfd != -1 && stderrfd != stdinfd && stderrfd != stdoutfd)
        close(stderrfd);

    check_open_fds(arg0);

    signal(SIGPIPE, SIG_DFL);
    /* in case our caller set it to IGN.  subprocesses are entitled
     * to assume they got DFL. */

    execvp(arg0, args);

    fprintf(stderr, "libxl: cannot execute %s: %s\n", arg0, strerror(errno));
    _exit(-1);
}

void libxl_report_child_exitstatus(libxl_ctx *ctx,
                                   xentoollog_level level,
                                   const char *what, pid_t pid, int status)
{

    if (WIFEXITED(status)) {
        int st = WEXITSTATUS(status);
        if (st)
            LIBXL__LOG(ctx, level, "%s [%ld] exited"
                   " with error status %d", what, (unsigned long)pid, st);
        else
            LIBXL__LOG(ctx, level, "%s [%ld] unexpectedly"
                   " exited status zero", what, (unsigned long)pid);
    } else if (WIFSIGNALED(status)) {
        int sig = WTERMSIG(status);
        const char *str = strsignal(sig);
        const char *coredump = WCOREDUMP(status) ? " (core dumped)" : "";
        if (str)
            LIBXL__LOG(ctx, level, "%s [%ld] died due to"
                   " fatal signal %s%s", what, (unsigned long)pid,
                   str, coredump);
        else
            LIBXL__LOG(ctx, level, "%s [%ld] died due to unknown"
                   " fatal signal number %d%s", what, (unsigned long)pid,
                   sig, coredump);
    } else {
        LIBXL__LOG(ctx, level, "%s [%ld] gave unknown"
               " wait status 0x%x", what, (unsigned long)pid, status);
    }
}

static int libxl__set_fd_flag(libxl__gc *gc, int fd, int flag)
{
    int flags;

    flags = fcntl(fd, F_GETFL);
    if (flags == -1)
        return ERROR_FAIL;

    flags |= flag;

    if (fcntl(fd, F_SETFL, flags) == -1)
        return ERROR_FAIL;

    return 0;
}

int libxl__spawn_spawn(libxl__gc *gc,
                      libxl__spawn_starting *for_spawn,
                      const char *what,
                      void (*intermediate_hook)(void *for_spawn,
                                                pid_t innerchild),
                      void *hook_data)
{
    libxl_ctx *ctx = libxl__gc_owner(gc);
    pid_t child, got;
    int status, rc;
    pid_t intermediate;
    int pipes[2];
    unsigned char dummy = 0;

    if (for_spawn) {
        for_spawn->what = strdup(what);
        if (!for_spawn->what) return ERROR_NOMEM;

        if (libxl_pipe(ctx, pipes) < 0)
            goto err_parent;
        if (libxl__set_fd_flag(gc, pipes[0], O_NONBLOCK) < 0 ||
            libxl__set_fd_flag(gc, pipes[1], O_NONBLOCK) < 0)
            goto err_parent_pipes;
    }

    intermediate = libxl_fork(ctx);
    if (intermediate ==-1)
        goto err_parent_pipes;

    if (intermediate) {
        /* parent */
        if (for_spawn) {
            for_spawn->intermediate = intermediate;
            for_spawn->fd = pipes[0];
            close(pipes[1]);
        }
        return 1;
    }

    /* we are now the intermediate process */
    if (for_spawn) close(pipes[0]);

    child = fork();
    if (child == -1)
        exit(255);
    if (!child) {
        if (for_spawn) close(pipes[1]);
        return 0; /* caller runs child code */
    }

    intermediate_hook(hook_data, child);

    if (!for_spawn) _exit(0); /* just detach then */

    got = call_waitpid(ctx->waitpid_instead, child, &status, 0);
    assert(got == child);

    rc = (WIFEXITED(status) ? WEXITSTATUS(status) :
          WIFSIGNALED(status) && WTERMSIG(status) < 127
          ? WTERMSIG(status)+128 : -1);
    if (for_spawn) {
        if (write(pipes[1], &dummy, sizeof(dummy)) != 1)
            perror("libxl__spawn_spawn: unable to signal child exit to parent");
    }
    _exit(rc);

 err_parent_pipes:
    if (for_spawn) {
        close(pipes[0]);
        close(pipes[1]);
    }

 err_parent:
    if (for_spawn) free(for_spawn->what);

    return ERROR_FAIL;
}

static void report_spawn_intermediate_status(libxl__gc *gc,
                                             libxl__spawn_starting *for_spawn,
                                             int status)
{
    if (!WIFEXITED(status)) {
        libxl_ctx *ctx = libxl__gc_owner(gc);
        char *intermediate_what;
        /* intermediate process did the logging itself if it exited */
        if ( asprintf(&intermediate_what,
                 "%s intermediate process (startup monitor)",
                 for_spawn->what) < 0 )
            intermediate_what = "intermediate process (startup monitor)";
        libxl_report_child_exitstatus(ctx, LIBXL__LOG_ERROR, intermediate_what,
                                      for_spawn->intermediate, status);
    }
}

int libxl__spawn_detach(libxl__gc *gc,
                       libxl__spawn_starting *for_spawn)
{
    libxl_ctx *ctx = libxl__gc_owner(gc);
    int r, status;
    pid_t got;
    int rc = 0;

    if (!for_spawn) return 0;

    if (for_spawn->intermediate) {
        r = kill(for_spawn->intermediate, SIGKILL);
        if (r) {
            LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
                         "could not kill %s intermediate process [%ld]",
                         for_spawn->what,
                         (unsigned long)for_spawn->intermediate);
            abort(); /* things are very wrong */
        }
        got = call_waitpid(ctx->waitpid_instead, for_spawn->intermediate, &status, 0);
        assert(got == for_spawn->intermediate);
        if (!(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL)) {
            report_spawn_intermediate_status(gc, for_spawn, status);
            rc = ERROR_FAIL;
        }
        for_spawn->intermediate = 0;
    }

    free(for_spawn->what);
    for_spawn->what = 0;

    return rc;
}

int libxl__spawn_check(libxl__gc *gc, void *for_spawn_void)
{
    libxl_ctx *ctx = libxl__gc_owner(gc);
    libxl__spawn_starting *for_spawn = for_spawn_void;
    pid_t got;
    int status;

    if (!for_spawn) return 0;

    assert(for_spawn->intermediate);
    got = call_waitpid(ctx->waitpid_instead, for_spawn->intermediate, &status, WNOHANG);
    if (!got) return 0;

    assert(got == for_spawn->intermediate);
    report_spawn_intermediate_status(gc, for_spawn, status);

    for_spawn->intermediate = 0;
    return ERROR_FAIL;
}