main.c   [plain text]

/*
 * main.c :  Main control function for svnserve
 *
 * ====================================================================
 *    Licensed to the Apache Software Foundation (ASF) under one
 *    or more contributor license agreements.  See the NOTICE file
 *    distributed with this work for additional information
 *    regarding copyright ownership.  The ASF licenses this file
 *    to you under the Apache License, Version 2.0 (the
 *    "License"); you may not use this file except in compliance
 *    with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing,
 *    software distributed under the License is distributed on an
 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *    KIND, either express or implied.  See the License for the
 *    specific language governing permissions and limitations
 *    under the License.
 * ====================================================================
 */



#define APR_WANT_STRFUNC
#include <apr_want.h>
#include <apr_general.h>
#include <apr_getopt.h>
#include <apr_network_io.h>
#include <apr_signal.h>
#include <apr_thread_proc.h>
#include <apr_portable.h>

#include <locale.h>

#include "svn_cmdline.h"
#include "svn_types.h"
#include "svn_pools.h"
#include "svn_error.h"
#include "svn_ra_svn.h"
#include "svn_utf.h"
#include "svn_dirent_uri.h"
#include "svn_path.h"
#include "svn_opt.h"
#include "svn_repos.h"
#include "svn_string.h"
#include "svn_cache_config.h"
#include "svn_version.h"
#include "svn_io.h"

#include "svn_private_config.h"
#include "private/svn_dep_compat.h"
#include "private/svn_atomic.h"
#include "winservice.h"

#ifdef HAVE_UNISTD_H
#include <unistd.h>   /* For getpid() */
#endif

#include "server.h"

/* The strategy for handling incoming connections.  Some of these may be
   unavailable due to platform limitations. */
enum connection_handling_mode {
  connection_mode_fork,   /* Create a process per connection */
  connection_mode_thread, /* Create a thread per connection */
  connection_mode_single  /* One connection at a time in this process */
};

/* The mode in which to run svnserve */
enum run_mode {
  run_mode_unspecified,
  run_mode_inetd,
  run_mode_daemon,
  run_mode_tunnel,
  run_mode_listen_once,
  run_mode_service
};

#if APR_HAS_FORK
#if APR_HAS_THREADS

#define CONNECTION_DEFAULT connection_mode_fork
#define CONNECTION_HAVE_THREAD_OPTION

#else /* ! APR_HAS_THREADS */

#define CONNECTION_DEFAULT connection_mode_fork

#endif /* ! APR_HAS_THREADS */
#elif APR_HAS_THREADS /* and ! APR_HAS_FORK */

#define CONNECTION_DEFAULT connection_mode_thread

#else /* ! APR_HAS_THREADS and ! APR_HAS_FORK */

#define CONNECTION_DEFAULT connection_mode_single

#endif


#ifdef WIN32
static apr_os_sock_t winservice_svnserve_accept_socket = INVALID_SOCKET;

/* The SCM calls this function (on an arbitrary thread, not the main()
   thread!) when it wants to stop the service.

   For now, our strategy is to close the listener socket, in order to
   unblock main() and cause it to exit its accept loop.  We cannot use
   apr_socket_close, because that function deletes the apr_socket_t
   structure, as well as closing the socket handle.  If we called
   apr_socket_close here, then main() will also call apr_socket_close,
   resulting in a double-free.  This way, we just close the kernel
   socket handle, which causes the accept() function call to fail,
   which causes main() to clean up the socket.  So, memory gets freed
   only once.

   This isn't pretty, but it's better than a lot of other options.
   Currently, there is no "right" way to shut down svnserve.

   We store the OS handle rather than a pointer to the apr_socket_t
   structure in order to eliminate any possibility of illegal memory
   access. */
void winservice_notify_stop(void)
{
  if (winservice_svnserve_accept_socket != INVALID_SOCKET)
    closesocket(winservice_svnserve_accept_socket);
}
#endif /* _WIN32 */


/* Option codes and descriptions for svnserve.
 *
 * The entire list must be terminated with an entry of nulls.
 *
 * APR requires that options without abbreviations
 * have codes greater than 255.
 */
#define SVNSERVE_OPT_LISTEN_PORT     256
#define SVNSERVE_OPT_LISTEN_HOST     257
#define SVNSERVE_OPT_FOREGROUND      258
#define SVNSERVE_OPT_TUNNEL_USER     259
#define SVNSERVE_OPT_VERSION         260
#define SVNSERVE_OPT_PID_FILE        261
#define SVNSERVE_OPT_SERVICE         262
#define SVNSERVE_OPT_CONFIG_FILE     263
#define SVNSERVE_OPT_LOG_FILE        264
#define SVNSERVE_OPT_CACHE_TXDELTAS  265
#define SVNSERVE_OPT_CACHE_FULLTEXTS 266

static const apr_getopt_option_t svnserve__options[] =
  {
    {"daemon",           'd', 0, N_("daemon mode")},
    {"inetd",            'i', 0, N_("inetd mode")},
    {"tunnel",           't', 0, N_("tunnel mode")},
    {"listen-once",      'X', 0, N_("listen-once mode (useful for debugging)")},
#ifdef WIN32
    {"service",          SVNSERVE_OPT_SERVICE, 0,
     N_("Windows service mode (Service Control Manager)")},
#endif
    {"root",             'r', 1, N_("root of directory to serve")},
    {"read-only",        'R', 0,
     N_("force read only, overriding repository config file")},
    {"config-file",      SVNSERVE_OPT_CONFIG_FILE, 1,
     N_("read configuration from file ARG")},
    {"listen-port",       SVNSERVE_OPT_LISTEN_PORT, 1,
#ifdef WIN32
     N_("listen port\n"
        "                             "
        "[mode: daemon, service, listen-once]")},
#else
     N_("listen port\n"
        "                             "
        "[mode: daemon, listen-once]")},
#endif
    {"listen-host",       SVNSERVE_OPT_LISTEN_HOST, 1,
#ifdef WIN32
     N_("listen hostname or IP address\n"
        "                             "
        "[mode: daemon, service, listen-once]")},
#else
     N_("listen hostname or IP address\n"
        "                             "
        "[mode: daemon, listen-once]")},
#endif
    {"prefer-ipv6",      '6', 0,
     N_("prefer IPv6 when resolving the listen hostname\n"
        "                             "
        "[IPv4 is preferred by default. Using IPv4 and IPv6\n"
        "                             "
        "at the same time is not supported in daemon mode.\n"
        "                             "
        "Use inetd mode or tunnel mode if you need this.]")},
    {"compression",      'c', 1,
     N_("compression level to use for network transmissions\n"
        "                             "
        "[0 .. no compression, 5 .. default, \n"
        "                             "
        " 9 .. maximum compression]")},
    {"memory-cache-size", 'M', 1,
     N_("size of the extra in-memory cache in MB used to\n"
        "                             "
        "minimize redundant operations.\n"
        "                             "
        "Default is 128 for threaded and 16 for non-\n"
        "                             "
        "threaded mode.\n"
        "                             "
        "[used for FSFS repositories only]")},
    {"cache-txdeltas", SVNSERVE_OPT_CACHE_TXDELTAS, 1,
     N_("enable or disable caching of deltas between older\n"
        "                             "
        "revisions.\n"
        "                             "
        "Default is no.\n"
        "                             "
        "[used for FSFS repositories only]")},
    {"cache-fulltexts", SVNSERVE_OPT_CACHE_FULLTEXTS, 1,
     N_("enable or disable caching of file contents\n"
        "                             "
        "Default is yes.\n"
        "                             "
        "[used for FSFS repositories only]")},
#ifdef CONNECTION_HAVE_THREAD_OPTION
    /* ### Making the assumption here that WIN32 never has fork and so
     * ### this option never exists when --service exists. */
    {"threads",          'T', 0, N_("use threads instead of fork "
                                    "[mode: daemon]")},
#endif
    {"foreground",        SVNSERVE_OPT_FOREGROUND, 0,
     N_("run in foreground (useful for debugging)\n"
        "                             "
        "[mode: daemon]")},
    {"log-file",         SVNSERVE_OPT_LOG_FILE, 1,
     N_("svnserve log file")},
    {"pid-file",         SVNSERVE_OPT_PID_FILE, 1,
#ifdef WIN32
     N_("write server process ID to file ARG\n"
        "                             "
        "[mode: daemon, listen-once, service]")},
#else
     N_("write server process ID to file ARG\n"
        "                             "
        "[mode: daemon, listen-once]")},
#endif
    {"tunnel-user",      SVNSERVE_OPT_TUNNEL_USER, 1,
     N_("tunnel username (default is current uid's name)\n"
        "                             "
        "[mode: tunnel]")},
    {"help",             'h', 0, N_("display this help")},
    {"version",           SVNSERVE_OPT_VERSION, 0,
     N_("show program version information")},
    {"quiet",            'q', 0,
     N_("no progress (only errors) to stderr")},
    {0,                  0,   0, 0}
  };


static void usage(const char *progname, apr_pool_t *pool)
{
  if (!progname)
    progname = "svnserve";

  svn_error_clear(svn_cmdline_fprintf(stderr, pool,
                                      _("Type '%s --help' for usage.\n"),
                                      progname));
  exit(1);
}

static void help(apr_pool_t *pool)
{
  apr_size_t i;

#ifdef WIN32
  svn_error_clear(svn_cmdline_fputs(_("usage: svnserve [-d | -i | -t | -X "
                                      "| --service] [options]\n"
                                      "\n"
                                      "Valid options:\n"),
                                    stdout, pool));
#else
  svn_error_clear(svn_cmdline_fputs(_("usage: svnserve [-d | -i | -t | -X] "
                                      "[options]\n"
                                      "\n"
                                      "Valid options:\n"),
                                    stdout, pool));
#endif
  for (i = 0; svnserve__options[i].name && svnserve__options[i].optch; i++)
    {
      const char *optstr;
      svn_opt_format_option(&optstr, svnserve__options + i, TRUE, pool);
      svn_error_clear(svn_cmdline_fprintf(stdout, pool, "  %s\n", optstr));
    }
  svn_error_clear(svn_cmdline_fprintf(stdout, pool, "\n"));
  exit(0);
}

static svn_error_t * version(svn_boolean_t quiet, apr_pool_t *pool)
{
  const char *fs_desc_start
    = _("The following repository back-end (FS) modules are available:\n\n");

  svn_stringbuf_t *version_footer;

  version_footer = svn_stringbuf_create(fs_desc_start, pool);
  SVN_ERR(svn_fs_print_modules(version_footer, pool));

#ifdef SVN_HAVE_SASL
  svn_stringbuf_appendcstr(version_footer,
                           _("\nCyrus SASL authentication is available.\n"));
#endif

  return svn_opt_print_help3(NULL, "svnserve", TRUE, quiet, version_footer->data,
                             NULL, NULL, NULL, NULL, NULL, pool);
}


#if APR_HAS_FORK
static void sigchld_handler(int signo)
{
  /* Nothing to do; we just need to interrupt the accept(). */
}
#endif

/* Redirect stdout to stderr.  ARG is the pool.
 *
 * In tunnel or inetd mode, we don't want hook scripts corrupting the
 * data stream by sending data to stdout, so we need to redirect
 * stdout somewhere else.  Sending it to stderr is acceptable; sending
 * it to /dev/null is another option, but apr doesn't provide a way to
 * do that without also detaching from the controlling terminal.
 */
static apr_status_t redirect_stdout(void *arg)
{
  apr_pool_t *pool = arg;
  apr_file_t *out_file, *err_file;
  apr_status_t apr_err;

  if ((apr_err = apr_file_open_stdout(&out_file, pool)))
    return apr_err;
  if ((apr_err = apr_file_open_stderr(&err_file, pool)))
    return apr_err;
  return apr_file_dup2(out_file, err_file, pool);
}

#if APR_HAS_THREADS
/* The pool passed to apr_thread_create can only be released when both

      A: the call to apr_thread_create has returned to the calling thread
      B: the new thread has started running and reached apr_thread_start_t

   So we set the atomic counter to 2 then both the calling thread and
   the new thread decrease it and when it reaches 0 the pool can be
   released.  */
struct shared_pool_t {
  svn_atomic_t count;
  apr_pool_t *pool;
};

static struct shared_pool_t *
attach_shared_pool(apr_pool_t *pool)
{
  struct shared_pool_t *shared = apr_palloc(pool, sizeof(struct shared_pool_t));

  shared->pool = pool;
  svn_atomic_set(&shared->count, 2);

  return shared;
}

static void
release_shared_pool(struct shared_pool_t *shared)
{
  if (svn_atomic_dec(&shared->count) == 0)
    svn_pool_destroy(shared->pool);
}
#endif

/* "Arguments" passed from the main thread to the connection thread */
struct serve_thread_t {
  svn_ra_svn_conn_t *conn;
  serve_params_t *params;
  struct shared_pool_t *shared_pool;
};

#if APR_HAS_THREADS
static void * APR_THREAD_FUNC serve_thread(apr_thread_t *tid, void *data)
{
  struct serve_thread_t *d = data;

  svn_error_clear(serve(d->conn, d->params, d->shared_pool->pool));
  release_shared_pool(d->shared_pool);

  return NULL;
}
#endif

/* Write the PID of the current process as a decimal number, followed by a
   newline to the file FILENAME, using POOL for temporary allocations. */
static svn_error_t *write_pid_file(const char *filename, apr_pool_t *pool)
{
  apr_file_t *file;
  const char *contents = apr_psprintf(pool, "%" APR_PID_T_FMT "\n",
                                             getpid());

  SVN_ERR(svn_io_remove_file2(filename, TRUE, pool));
  SVN_ERR(svn_io_file_open(&file, filename,
                           APR_WRITE | APR_CREATE | APR_EXCL,
                           APR_OS_DEFAULT, pool));
  SVN_ERR(svn_io_file_write_full(file, contents, strlen(contents), NULL,
                                 pool));

  SVN_ERR(svn_io_file_close(file, pool));

  return SVN_NO_ERROR;
}

/* Version compatibility check */
static svn_error_t *
check_lib_versions(void)
{
  static const svn_version_checklist_t checklist[] =
    {
      { "svn_subr",  svn_subr_version },
      { "svn_repos", svn_repos_version },
      { "svn_fs",    svn_fs_version },
      { "svn_delta", svn_delta_version },
      { "svn_ra_svn", svn_ra_svn_version },
      { NULL, NULL }
    };

  SVN_VERSION_DEFINE(my_version);
  return svn_ver_check_list(&my_version, checklist);
}


int main(int argc, const char *argv[])
{
  enum run_mode run_mode = run_mode_unspecified;
  svn_boolean_t foreground = FALSE;
  apr_socket_t *sock, *usock;
  apr_file_t *in_file, *out_file;
  apr_sockaddr_t *sa;
  apr_pool_t *pool;
  apr_pool_t *connection_pool;
  apr_allocator_t *allocator;
  svn_error_t *err;
  apr_getopt_t *os;
  int opt;
  serve_params_t params;
  const char *arg;
  apr_status_t status;
  svn_ra_svn_conn_t *conn;
  apr_proc_t proc;
#if APR_HAS_THREADS
  apr_threadattr_t *tattr;
  apr_thread_t *tid;
  struct shared_pool_t *shared_pool;

  struct serve_thread_t *thread_data;
#endif
  enum connection_handling_mode handling_mode = CONNECTION_DEFAULT;
  apr_uint16_t port = SVN_RA_SVN_PORT;
  const char *host = NULL;
  int family = APR_INET;
  apr_int32_t sockaddr_info_flags = 0;
  svn_boolean_t prefer_v6 = FALSE;
  svn_boolean_t quiet = FALSE;
  svn_boolean_t is_version = FALSE;
  int mode_opt_count = 0;
  const char *config_filename = NULL;
  const char *pid_filename = NULL;
  const char *log_filename = NULL;
  svn_node_kind_t kind;

  /* Initialize the app. */
  if (svn_cmdline_init("svnserve", stderr) != EXIT_SUCCESS)
    return EXIT_FAILURE;

  /* Create our top-level pool. */
  pool = svn_pool_create(NULL);

#ifdef SVN_HAVE_SASL
  SVN_INT_ERR(cyrus_init(pool));
#endif

  /* Check library versions */
  err = check_lib_versions();
  if (err)
    return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");

  /* Initialize the FS library. */
  err = svn_fs_initialize(pool);
  if (err)
    return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");

  err = svn_cmdline__getopt_init(&os, argc, argv, pool);
  if (err)
    return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");

  params.root = "/";
  params.tunnel = FALSE;
  params.tunnel_user = NULL;
  params.read_only = FALSE;
  params.cfg = NULL;
  params.pwdb = NULL;
  params.authzdb = NULL;
  params.compression_level = SVN_DELTA_COMPRESSION_LEVEL_DEFAULT;
  params.log_file = NULL;
  params.username_case = CASE_ASIS;
  params.memory_cache_size = (apr_uint64_t)-1;
  params.cache_fulltexts = TRUE;
  params.cache_txdeltas = FALSE;

  while (1)
    {
      status = apr_getopt_long(os, svnserve__options, &opt, &arg);
      if (APR_STATUS_IS_EOF(status))
        break;
      if (status != APR_SUCCESS)
        usage(argv[0], pool);
      switch (opt)
        {
        case '6':
          prefer_v6 = TRUE;
          break;

        case 'h':
          help(pool);
          break;

        case 'q':
          quiet = TRUE;
          break;

        case SVNSERVE_OPT_VERSION:
          is_version = TRUE;
          break;

        case 'd':
          if (run_mode != run_mode_daemon)
            {
              run_mode = run_mode_daemon;
              mode_opt_count++;
            }
          break;

        case SVNSERVE_OPT_FOREGROUND:
          foreground = TRUE;
          break;

        case 'i':
          if (run_mode != run_mode_inetd)
            {
              run_mode = run_mode_inetd;
              mode_opt_count++;
            }
          break;

        case SVNSERVE_OPT_LISTEN_PORT:
          {
            apr_uint64_t val;

            err = svn_cstring_strtoui64(&val, arg, 0, APR_UINT16_MAX, 10);
            if (err)
              return svn_cmdline_handle_exit_error(
                       svn_error_createf(SVN_ERR_CL_ARG_PARSING_ERROR, err,
                                         _("Invalid port '%s'"), arg),
                       pool, "svnserve: ");
            port = (apr_uint16_t)val;
          }
          break;

        case SVNSERVE_OPT_LISTEN_HOST:
          host = arg;
          break;

        case 't':
          if (run_mode != run_mode_tunnel)
            {
              run_mode = run_mode_tunnel;
              mode_opt_count++;
            }
          break;

        case SVNSERVE_OPT_TUNNEL_USER:
          params.tunnel_user = arg;
          break;

        case 'X':
          if (run_mode != run_mode_listen_once)
            {
              run_mode = run_mode_listen_once;
              mode_opt_count++;
            }
          break;

        case 'r':
          SVN_INT_ERR(svn_utf_cstring_to_utf8(&params.root, arg, pool));

          err = svn_io_check_resolved_path(params.root, &kind, pool);
          if (err)
            return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
          if (kind != svn_node_dir)
            {
              svn_error_clear
                (svn_cmdline_fprintf
                   (stderr, pool,
                    _("svnserve: Root path '%s' does not exist "
                      "or is not a directory.\n"), params.root));
              return EXIT_FAILURE;
            }

          params.root = svn_dirent_internal_style(params.root, pool);
          SVN_INT_ERR(svn_dirent_get_absolute(&params.root, params.root, pool));
          break;

        case 'R':
          params.read_only = TRUE;
          break;

        case 'T':
          handling_mode = connection_mode_thread;
          break;

        case 'c':
          params.compression_level = atoi(arg);
          if (params.compression_level < SVN_DELTA_COMPRESSION_LEVEL_NONE)
            params.compression_level = SVN_DELTA_COMPRESSION_LEVEL_NONE;
          if (params.compression_level > SVN_DELTA_COMPRESSION_LEVEL_MAX)
            params.compression_level = SVN_DELTA_COMPRESSION_LEVEL_MAX;
          break;

        case 'M':
          params.memory_cache_size = 0x100000 * apr_strtoi64(arg, NULL, 0);
          break;

        case SVNSERVE_OPT_CACHE_TXDELTAS:
          params.cache_txdeltas
             = svn_tristate__from_word(arg) == svn_tristate_true;
          break;

        case SVNSERVE_OPT_CACHE_FULLTEXTS:
          params.cache_fulltexts
             = svn_tristate__from_word(arg) == svn_tristate_true;
          break;

#ifdef WIN32
        case SVNSERVE_OPT_SERVICE:
          if (run_mode != run_mode_service)
            {
              run_mode = run_mode_service;
              mode_opt_count++;
            }
          break;
#endif

        case SVNSERVE_OPT_CONFIG_FILE:
          SVN_INT_ERR(svn_utf_cstring_to_utf8(&config_filename, arg, pool));
          config_filename = svn_dirent_internal_style(config_filename, pool);
          SVN_INT_ERR(svn_dirent_get_absolute(&config_filename, config_filename,
                                              pool));
          break;

        case SVNSERVE_OPT_PID_FILE:
          SVN_INT_ERR(svn_utf_cstring_to_utf8(&pid_filename, arg, pool));
          pid_filename = svn_dirent_internal_style(pid_filename, pool);
          SVN_INT_ERR(svn_dirent_get_absolute(&pid_filename, pid_filename,
                                              pool));
          break;

        case SVNSERVE_OPT_LOG_FILE:
          SVN_INT_ERR(svn_utf_cstring_to_utf8(&log_filename, arg, pool));
          log_filename = svn_dirent_internal_style(log_filename, pool);
          SVN_INT_ERR(svn_dirent_get_absolute(&log_filename, log_filename,
                                              pool));
          break;

        }
    }

  if (is_version)
    {
      SVN_INT_ERR(version(quiet, pool));
      exit(0);
    }

  if (os->ind != argc)
    usage(argv[0], pool);

  if (mode_opt_count != 1)
    {
      svn_error_clear(svn_cmdline_fputs(
#ifdef WIN32
                      _("You must specify exactly one of -d, -i, -t, "
                        "--service or -X.\n"),
#else
                      _("You must specify exactly one of -d, -i, -t or -X.\n"),
#endif
                       stderr, pool));
      usage(argv[0], pool);
    }

  /* If a configuration file is specified, load it and any referenced
   * password and authorization files. */
  if (config_filename)
    SVN_INT_ERR(load_configs(&params.cfg, &params.pwdb, &params.authzdb,
                             &params.username_case, config_filename, TRUE,
                             svn_dirent_dirname(config_filename, pool),
                             NULL, NULL, /* server baton, conn */
                             pool));

  if (log_filename)
    SVN_INT_ERR(svn_io_file_open(&params.log_file, log_filename,
                                 APR_WRITE | APR_CREATE | APR_APPEND,
                                 APR_OS_DEFAULT, pool));

  if (params.tunnel_user && run_mode != run_mode_tunnel)
    {
      svn_error_clear
        (svn_cmdline_fprintf
           (stderr, pool,
            _("Option --tunnel-user is only valid in tunnel mode.\n")));
      exit(1);
    }

  if (run_mode == run_mode_inetd || run_mode == run_mode_tunnel)
    {
      params.tunnel = (run_mode == run_mode_tunnel);
      apr_pool_cleanup_register(pool, pool, apr_pool_cleanup_null,
                                redirect_stdout);
      status = apr_file_open_stdin(&in_file, pool);
      if (status)
        {
          err = svn_error_wrap_apr(status, _("Can't open stdin"));
          return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
        }

      status = apr_file_open_stdout(&out_file, pool);
      if (status)
        {
          err = svn_error_wrap_apr(status, _("Can't open stdout"));
          return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
        }

      /* Use a subpool for the connection to ensure that if SASL is used
       * the pool cleanup handlers that call sasl_dispose() (connection_pool)
       * and sasl_done() (pool) are run in the right order. See issue #3664. */
      connection_pool = svn_pool_create(pool);
      conn = svn_ra_svn_create_conn2(NULL, in_file, out_file,
                                     params.compression_level,
                                     connection_pool);
      svn_error_clear(serve(conn, &params, connection_pool));
      exit(0);
    }

#ifdef WIN32
  /* If svnserve needs to run as a Win32 service, then we need to
     coordinate with the Service Control Manager (SCM) before
     continuing.  This function call registers the svnserve.exe
     process with the SCM, waits for the "start" command from the SCM
     (which will come very quickly), and confirms that those steps
     succeeded.

     After this call succeeds, the service is free to run.  At some
     point in the future, the SCM will send a message to the service,
     requesting that it stop.  This is translated into a call to
     winservice_notify_stop().  The service is then responsible for
     cleanly terminating.

     We need to do this before actually starting the service logic
     (opening files, sockets, etc.) because the SCM wants you to
     connect *first*, then do your service-specific logic.  If the
     service process takes too long to connect to the SCM, then the
     SCM will decide that the service is busted, and will give up on
     it.
     */
  if (run_mode == run_mode_service)
    {
      err = winservice_start();
      if (err)
        {
          svn_handle_error2(err, stderr, FALSE, "svnserve: ");

          /* This is the most common error.  It means the user started
             svnserve from a shell, and specified the --service
             argument.  svnserve cannot be started, as a service, in
             this way.  The --service argument is valid only valid if
             svnserve is started by the SCM. */
          if (err->apr_err ==
              APR_FROM_OS_ERROR(ERROR_FAILED_SERVICE_CONTROLLER_CONNECT))
            {
              svn_error_clear(svn_cmdline_fprintf(stderr, pool,
                  _("svnserve: The --service flag is only valid if the"
                    " process is started by the Service Control Manager.\n")));
            }

          svn_error_clear(err);
          exit(1);
        }

      /* The service is now in the "starting" state.  Before the SCM will
         consider the service "started", this thread must call the
         winservice_running() function. */
    }
#endif /* WIN32 */

  /* Make sure we have IPV6 support first before giving apr_sockaddr_info_get
     APR_UNSPEC, because it may give us back an IPV6 address even if we can't
     create IPV6 sockets. */

#if APR_HAVE_IPV6
#ifdef MAX_SECS_TO_LINGER
  /* ### old APR interface */
  status = apr_socket_create(&sock, APR_INET6, SOCK_STREAM, pool);
#else
  status = apr_socket_create(&sock, APR_INET6, SOCK_STREAM, APR_PROTO_TCP,
                             pool);
#endif
  if (status == 0)
    {
      apr_socket_close(sock);
      family = APR_UNSPEC;

      if (prefer_v6)
        {
          if (host == NULL)
            host = "::";
          sockaddr_info_flags = APR_IPV6_ADDR_OK;
        }
      else
        {
          if (host == NULL)
            host = "0.0.0.0";
          sockaddr_info_flags = APR_IPV4_ADDR_OK;
        }
    }
#endif

  status = apr_sockaddr_info_get(&sa, host, family, port,
                                 sockaddr_info_flags, pool);
  if (status)
    {
      err = svn_error_wrap_apr(status, _("Can't get address info"));
      return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
    }


#ifdef MAX_SECS_TO_LINGER
  /* ### old APR interface */
  status = apr_socket_create(&sock, sa->family, SOCK_STREAM, pool);
#else
  status = apr_socket_create(&sock, sa->family, SOCK_STREAM, APR_PROTO_TCP,
                             pool);
#endif
  if (status)
    {
      err = svn_error_wrap_apr(status, _("Can't create server socket"));
      return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
    }

  /* Prevents "socket in use" errors when server is killed and quickly
   * restarted. */
  apr_socket_opt_set(sock, APR_SO_REUSEADDR, 1);

  status = apr_socket_bind(sock, sa);
  if (status)
    {
      err = svn_error_wrap_apr(status, _("Can't bind server socket"));
      return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
    }

  apr_socket_listen(sock, 7);

#if APR_HAS_FORK
  if (run_mode != run_mode_listen_once && !foreground)
    apr_proc_detach(APR_PROC_DETACH_DAEMONIZE);

  apr_signal(SIGCHLD, sigchld_handler);
#endif

#ifdef SIGPIPE
  /* Disable SIGPIPE generation for the platforms that have it. */
  apr_signal(SIGPIPE, SIG_IGN);
#endif

#ifdef SIGXFSZ
  /* Disable SIGXFSZ generation for the platforms that have it, otherwise
   * working with large files when compiled against an APR that doesn't have
   * large file support will crash the program, which is uncool. */
  apr_signal(SIGXFSZ, SIG_IGN);
#endif

  if (pid_filename)
    SVN_INT_ERR(write_pid_file(pid_filename, pool));

#ifdef WIN32
  status = apr_os_sock_get(&winservice_svnserve_accept_socket, sock);
  if (status)
    winservice_svnserve_accept_socket = INVALID_SOCKET;

  /* At this point, the service is "running".  Notify the SCM. */
  if (run_mode == run_mode_service)
    winservice_running();
#endif

  /* Configure FS caches for maximum efficiency with svnserve.
   * For pre-forked (i.e. multi-processed) mode of operation,
   * keep the per-process caches smaller than the default.
   * Also, apply the respective command line parameters, if given. */
  {
    svn_cache_config_t settings = *svn_cache_config_get();

    if (params.memory_cache_size != -1)
      settings.cache_size = params.memory_cache_size;

    settings.single_threaded = TRUE;
    if (handling_mode == connection_mode_thread)
      {
#if APR_HAS_THREADS
        settings.single_threaded = FALSE;
#else
        /* No requests will be processed at all
         * (see "switch (handling_mode)" code further down).
         * But if they were, some other synchronization code
         * would need to take care of securing integrity of
         * APR-based structures. That would include our caches.
         */
#endif
      }

    svn_cache_config_set(&settings);
  }

  while (1)
    {
#ifdef WIN32
      if (winservice_is_stopping())
        return ERROR_SUCCESS;
#endif

      /* If we are using fulltext caches etc. we will allocate many large
         chunks of memory of various sizes outside the cache for those
         fulltexts. Make sure we use the memory wisely: use an allocator
         that causes memory fragments to be given back to the OS early. */

      if (apr_allocator_create(&allocator))
        return EXIT_FAILURE;

      apr_allocator_max_free_set(allocator, SVN_ALLOCATOR_RECOMMENDED_MAX_FREE);

      /* Non-standard pool handling.  The main thread never blocks to join
         the connection threads so it cannot clean up after each one.  So
         separate pools that can be cleared at thread exit are used. */

      connection_pool = svn_pool_create_ex(NULL, allocator);
      apr_allocator_owner_set(allocator, connection_pool);

      status = apr_socket_accept(&usock, sock, connection_pool);
      if (handling_mode == connection_mode_fork)
        {
          /* Collect any zombie child processes. */
          while (apr_proc_wait_all_procs(&proc, NULL, NULL, APR_NOWAIT,
                                         connection_pool) == APR_CHILD_DONE)
            ;
        }
      if (APR_STATUS_IS_EINTR(status)
          || APR_STATUS_IS_ECONNABORTED(status)
          || APR_STATUS_IS_ECONNRESET(status))
        {
          svn_pool_destroy(connection_pool);
          continue;
        }
      if (status)
        {
          err = svn_error_wrap_apr
            (status, _("Can't accept client connection"));
          return svn_cmdline_handle_exit_error(err, pool, "svnserve: ");
        }

      /* Enable TCP keep-alives on the socket so we time out when
       * the connection breaks due to network-layer problems.
       * If the peer has dropped the connection due to a network partition
       * or a crash, or if the peer no longer considers the connection
       * valid because we are behind a NAT and our public IP has changed,
       * it will respond to the keep-alive probe with a RST instead of an
       * acknowledgment segment, which will cause svn to abort the session
       * even while it is currently blocked waiting for data from the peer. */
      status = apr_socket_opt_set(usock, APR_SO_KEEPALIVE, 1);
      if (status)
        {
          /* It's not a fatal error if we cannot enable keep-alives. */
        }

      conn = svn_ra_svn_create_conn2(usock, NULL, NULL,
                                     params.compression_level,
                                     connection_pool);

      if (run_mode == run_mode_listen_once)
        {
          err = serve(conn, &params, connection_pool);

          if (err)
            svn_handle_error2(err, stdout, FALSE, "svnserve: ");
          svn_error_clear(err);

          apr_socket_close(usock);
          apr_socket_close(sock);
          exit(0);
        }

      switch (handling_mode)
        {
        case connection_mode_fork:
#if APR_HAS_FORK
          status = apr_proc_fork(&proc, connection_pool);
          if (status == APR_INCHILD)
            {
              apr_socket_close(sock);
              err = serve(conn, &params, connection_pool);
              log_error(err, params.log_file,
                        svn_ra_svn_conn_remote_host(conn),
                        NULL, NULL, /* user, repos */
                        connection_pool);
              svn_error_clear(err);
              apr_socket_close(usock);
              exit(0);
            }
          else if (status == APR_INPARENT)
            {
              apr_socket_close(usock);
            }
          else
            {
              err = svn_error_wrap_apr(status, "apr_proc_fork");
              log_error(err, params.log_file,
                        svn_ra_svn_conn_remote_host(conn),
                        NULL, NULL, /* user, repos */
                        connection_pool);
              svn_error_clear(err);
              apr_socket_close(usock);
            }
          svn_pool_destroy(connection_pool);
#endif
          break;

        case connection_mode_thread:
          /* Create a detached thread for each connection.  That's not a
             particularly sophisticated strategy for a threaded server, it's
             little different from forking one process per connection. */
#if APR_HAS_THREADS
          shared_pool = attach_shared_pool(connection_pool);
          status = apr_threadattr_create(&tattr, connection_pool);
          if (status)
            {
              err = svn_error_wrap_apr(status, _("Can't create threadattr"));
              svn_handle_error2(err, stderr, FALSE, "svnserve: ");
              svn_error_clear(err);
              exit(1);
            }
          status = apr_threadattr_detach_set(tattr, 1);
          if (status)
            {
              err = svn_error_wrap_apr(status, _("Can't set detached state"));
              svn_handle_error2(err, stderr, FALSE, "svnserve: ");
              svn_error_clear(err);
              exit(1);
            }
          thread_data = apr_palloc(connection_pool, sizeof(*thread_data));
          thread_data->conn = conn;
          thread_data->params = &params;
          thread_data->shared_pool = shared_pool;
          status = apr_thread_create(&tid, tattr, serve_thread, thread_data,
                                     shared_pool->pool);
          if (status)
            {
              err = svn_error_wrap_apr(status, _("Can't create thread"));
              svn_handle_error2(err, stderr, FALSE, "svnserve: ");
              svn_error_clear(err);
              exit(1);
            }
          release_shared_pool(shared_pool);
#endif
          break;

        case connection_mode_single:
          /* Serve one connection at a time. */
          svn_error_clear(serve(conn, &params, connection_pool));
          svn_pool_destroy(connection_pool);
        }
    }

  /* NOTREACHED */
}