lib/daemon.c

   1 /*
   2  * Copyright (c) 2014 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #include <config.h>
  17 #include "daemon.h"
  18 #include "daemon-private.h"
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <unistd.h>
  22 #include "util.h"
  23 #include "ovs-thread.h"
  24 #include "openvswitch/vlog.h"
  25
  26 VLOG_DEFINE_THIS_MODULE(daemon);
  27
  28 /* For each of the standard file descriptors, whether to replace it by
  29  * /dev/null (if false) or keep it for the daemon to use (if true). */
  30 static bool save_fds[3];
  31
  32 /* Self Confinement is a security feature that introduces additional
  33  * layer of defense where OVS in self-denying manner would refuse to connect
  34  * to or create unix domain sockets outside designated 'run' directory even
  35  * if remote (or local) OVSDB manager asked it to do so.  This feature may
  36  * be disabled if Mandatory Access Control is used. */
  37 static bool self_confine = true;
  38
  39 /* Will daemonize() really detach? */
  40 bool
  41 get_detach(void)
  42 {
  43     return detach;
  44 }
  45
  46 /* If configured with set_pidfile() or set_detach(), creates the pid file and
  47  * detaches from the foreground session.  */
  48 void
  49 daemonize(void)
  50 {
  51     daemonize_start(false);
  52     daemonize_complete();
  53 }
  54
  55 /* Sets up a following call to daemonize() to create a pidfile named 'name'.
  56  * If 'name' begins with '/' (or contains ':' in windows), then it is treated
  57  * as an absolute path. Otherwise, it is taken relative to RUNDIR,
  58  * which is $(prefix)/var/run by default.
  59  *
  60  * If 'name' is null, then program_name followed by ".pid" is used. */
  61 void
  62 set_pidfile(const char *name)
  63 {
  64     assert_single_threaded();
  65     free(pidfile);
  66     pidfile = make_pidfile_name(name);
  67 }
  68
  69 /* Disables self confinement. */
  70 void
  71 daemon_disable_self_confinement(void)
  72 {
  73     self_confine = false;
  74 }
  75
  76 /* Returns true, if self-confinement should be enforced.
  77  * Otherwise, returns false. */
  78 bool
  79 daemon_should_self_confine(void)
  80 {
  81     return self_confine;
  82 }
  83
  84 /* A daemon doesn't normally have any use for the file descriptors for stdin,
  85  * stdout, and stderr after it detaches.  To keep these file descriptors from
  86  * e.g. holding an SSH session open, by default detaching replaces each of
  87  * these file descriptors by /dev/null.  But a few daemons expect the user to
  88  * redirect stdout or stderr to a file, in which case it is desirable to keep
  89  * these file descriptors.  This function, therefore, disables replacing 'fd'
  90  * by /dev/null when the daemon detaches. */
  91 void
  92 daemon_save_fd(int fd)
  93 {
  94     ovs_assert(fd == STDIN_FILENO ||
  95                fd == STDOUT_FILENO ||
  96                fd == STDERR_FILENO);
  97     save_fds[fd] = true;
  98 }
  99
 100 /* Returns a readable and writable fd for /dev/null, if successful, otherwise
 101  * a negative errno value.  The caller must not close the returned fd (because
 102  * the same fd will be handed out to subsequent callers). */
 103 static int
 104 get_null_fd(void)
 105 {
 106     static int null_fd;
 107 #ifndef _WIN32
 108     char *device = "/dev/null";
 109 #else
 110     char *device = "nul";
 111 #endif
 112
 113     if (!null_fd) {
 114         null_fd = open(device, O_RDWR);
 115         if (null_fd < 0) {
 116             int error = errno;
 117             VLOG_ERR("could not open %s: %s", device, ovs_strerror(error));
 118             null_fd = -error;
 119         }
 120     }
 121
 122     return null_fd;
 123 }
 124
 125 /* Close standard file descriptors (except any that the client has requested we
 126  * leave open by calling daemon_save_fd()).  If we're started from e.g. an SSH
 127  * session, then this keeps us from holding that session open artificially. */
 128 void
 129 close_standard_fds(void)
 130 {
 131     int null_fd = get_null_fd();
 132     if (null_fd >= 0) {
 133         int fd;
 134
 135         for (fd = 0; fd < 3; fd++) {
 136             if (!save_fds[fd]) {
 137                 dup2(null_fd, fd);
 138             }
 139         }
 140     }
 141
 142     /* Disable logging to stderr to avoid wasting CPU time. */
 143     vlog_set_levels(NULL, VLF_CONSOLE, VLL_OFF);
 144 }