lib/tevent/tevent_standard.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    main select loop and event handling
   4    Copyright (C) Stefan Metzmacher      2013
   5    Copyright (C) Jeremy Allison         2013
   6
   7      ** NOTE! The following LGPL license applies to the tevent
   8      ** library. This does NOT imply that all of Samba is released
   9      ** under the LGPL
  10
  11    This library is free software; you can redistribute it and/or
  12    modify it under the terms of the GNU Lesser General Public
  13    License as published by the Free Software Foundation; either
  14    version 3 of the License, or (at your option) any later version.
  15
  16    This library is distributed in the hope that it will be useful,
  17    but WITHOUT ANY WARRANTY; without even the implied warranty of
  18    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19    Lesser General Public License for more details.
  20
  21    You should have received a copy of the GNU Lesser General Public
  22    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  23 */
  24
  25 /*
  26   This is SAMBA's default event loop code
  27
  28   - we try to use epoll if configure detected support for it
  29     otherwise we use poll()
  30   - if epoll is broken on the system or the kernel doesn't support it
  31     at runtime we fallback to poll()
  32 */
  33
  34 #include "replace.h"
  35 #include "tevent.h"
  36 #include "tevent_util.h"
  37 #include "tevent_internal.h"
  38
  39 struct std_event_glue {
  40         const struct tevent_ops *epoll_ops;
  41         const struct tevent_ops *poll_ops;
  42         struct tevent_ops *glue_ops;
  43         bool fallback_replay;
  44 };
  45
  46 static int std_event_context_init(struct tevent_context *ev);
  47
  48 static const struct tevent_ops std_event_ops = {
  49         .context_init           = std_event_context_init,
  50 };
  51
  52 /*
  53   If this function gets called. epoll failed at runtime.
  54   Move us to using poll instead. If we return false here,
  55   caller should abort().
  56 */
  57 static bool std_fallback_to_poll(struct tevent_context *ev, bool replay)
  58 {
  59         void *glue_ptr = talloc_parent(ev->ops);
  60         struct std_event_glue *glue =
  61                 talloc_get_type_abort(glue_ptr,
  62                 struct std_event_glue);
  63         int ret;
  64         struct tevent_fd *fde;
  65         struct tevent_fd *fde_next;
  66
  67         glue->fallback_replay = replay;
  68
  69         /* First switch all the ops to poll. */
  70         glue->epoll_ops = NULL;
  71
  72         /*
  73          * Set custom_ops the same as poll.
  74          */
  75         *glue->glue_ops = *glue->poll_ops;
  76         glue->glue_ops->context_init = std_event_context_init;
  77
  78         /* Next initialize the poll backend. */
  79         ret = glue->poll_ops->context_init(ev);
  80         if (ret != 0) {
  81                 return false;
  82         }
  83
  84         /*
  85          * Now we have to change all the existing file descriptor
  86          * events from the epoll backend to the poll backend.
  87          */
  88         for (fde = ev->fd_events; fde; fde = fde_next) {
  89                 /*
  90                  * We must remove this fde off the ev->fd_events list.
  91                  */
  92                 fde_next = fde->next;
  93
  94                 /* Remove from the ev->fd_events list. */
  95                 DLIST_REMOVE(ev->fd_events, fde);
  96
  97                 /* Re-add this event as a poll backend event. */
  98                 tevent_poll_event_add_fd_internal(ev, fde);
  99         }
 100
 101         return true;
 102 }
 103
 104 static int std_event_loop_once(struct tevent_context *ev, const char *location)
 105 {
 106         void *glue_ptr = talloc_parent(ev->ops);
 107         struct std_event_glue *glue =
 108                 talloc_get_type_abort(glue_ptr,
 109                 struct std_event_glue);
 110         int ret;
 111
 112         ret = glue->epoll_ops->loop_once(ev, location);
 113         if (glue->epoll_ops != NULL) {
 114                 /* No fallback */
 115                 return ret;
 116         }
 117
 118         if (!glue->fallback_replay) {
 119                 /*
 120                  * The problem happened while modifying an event.
 121                  * An event handler was triggered in this case
 122                  * and there is no need to call loop_once() again.
 123                  */
 124                 return ret;
 125         }
 126
 127         return glue->poll_ops->loop_once(ev, location);
 128 }
 129
 130 static int std_event_loop_wait(struct tevent_context *ev, const char *location)
 131 {
 132         void *glue_ptr = talloc_parent(ev->ops);
 133         struct std_event_glue *glue =
 134                 talloc_get_type_abort(glue_ptr,
 135                 struct std_event_glue);
 136         int ret;
 137
 138         ret = glue->epoll_ops->loop_wait(ev, location);
 139         if (glue->epoll_ops != NULL) {
 140                 /* No fallback */
 141                 return ret;
 142         }
 143
 144         return glue->poll_ops->loop_wait(ev, location);
 145 }
 146 /*
 147   Initialize the epoll backend and allow it to call a
 148   switch function if epoll fails at runtime.
 149 */
 150 static int std_event_context_init(struct tevent_context *ev)
 151 {
 152         struct std_event_glue *glue;
 153         int ret;
 154
 155         /*
 156          * If this is the first initialization
 157          * we need to set up the allocated ops
 158          * pointers.
 159          */
 160
 161         if (ev->ops == &std_event_ops) {
 162                 glue = talloc_zero(ev, struct std_event_glue);
 163                 if (glue == NULL) {
 164                         return -1;
 165                 }
 166
 167                 glue->epoll_ops = tevent_find_ops_byname("epoll");
 168
 169                 glue->poll_ops = tevent_find_ops_byname("poll");
 170                 if (glue->poll_ops == NULL) {
 171                         return -1;
 172                 }
 173
 174                 /*
 175                  * Allocate space for our custom ops.
 176                  * Allocate as a child of our epoll_ops pointer
 177                  * so we can easily get to it using talloc_parent.
 178                  */
 179                 glue->glue_ops = talloc_zero(glue, struct tevent_ops);
 180                 if (glue->glue_ops == NULL) {
 181                         talloc_free(glue);
 182                         return -1;
 183                 }
 184
 185                 ev->ops = glue->glue_ops;
 186         } else {
 187                 void *glue_ptr = talloc_parent(ev->ops);
 188                 glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 189         }
 190
 191         if (glue->epoll_ops != NULL) {
 192                 /*
 193                  * Set custom_ops the same as epoll,
 194                  * except re-init using std_event_context_init()
 195                  * and use std_event_loop_once() to add the
 196                  * ability to fallback to a poll backend on
 197                  * epoll runtime error.
 198                  */
 199                 *glue->glue_ops = *glue->epoll_ops;
 200                 glue->glue_ops->context_init = std_event_context_init;
 201                 glue->glue_ops->loop_once = std_event_loop_once;
 202                 glue->glue_ops->loop_wait = std_event_loop_wait;
 203
 204                 ret = glue->epoll_ops->context_init(ev);
 205                 if (ret == -1) {
 206                         goto fallback;
 207                 }
 208 #ifdef HAVE_EPOLL
 209                 if (!tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll)) {
 210                         TALLOC_FREE(ev->additional_data);
 211                         goto fallback;
 212                 }
 213 #endif
 214
 215                 return ret;
 216         }
 217
 218 fallback:
 219         glue->epoll_ops = NULL;
 220
 221         /*
 222          * Set custom_ops the same as poll.
 223          */
 224         *glue->glue_ops = *glue->poll_ops;
 225         glue->glue_ops->context_init = std_event_context_init;
 226
 227         return glue->poll_ops->context_init(ev);
 228 }
 229
 230 _PRIVATE_ bool tevent_standard_init(void)
 231 {
 232         return tevent_register_backend("standard", &std_event_ops);
 233 }