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 #ifdef HAVE_EPOLL
  58 static bool std_fallback_to_poll(struct tevent_context *ev, bool replay)
  59 {
  60         void *glue_ptr = talloc_parent(ev->ops);
  61         struct std_event_glue *glue =
  62                 talloc_get_type_abort(glue_ptr,
  63                 struct std_event_glue);
  64         int ret;
  65         struct tevent_fd *fde;
  66         struct tevent_fd *fde_next;
  67
  68         glue->fallback_replay = replay;
  69
  70         /* First switch all the ops to poll. */
  71         glue->epoll_ops = NULL;
  72
  73         /*
  74          * Set custom_ops the same as poll.
  75          */
  76         *glue->glue_ops = *glue->poll_ops;
  77         glue->glue_ops->context_init = std_event_context_init;
  78
  79         /* Next initialize the poll backend. */
  80         ret = glue->poll_ops->context_init(ev);
  81         if (ret != 0) {
  82                 return false;
  83         }
  84
  85         /*
  86          * Now we have to change all the existing file descriptor
  87          * events from the epoll backend to the poll backend.
  88          */
  89         for (fde = ev->fd_events; fde; fde = fde_next) {
  90                 /*
  91                  * We must remove this fde off the ev->fd_events list.
  92                  */
  93                 fde_next = fde->next;
  94
  95                 /* Remove from the ev->fd_events list. */
  96                 DLIST_REMOVE(ev->fd_events, fde);
  97
  98                 /* Re-add this event as a poll backend event. */
  99                 tevent_poll_event_add_fd_internal(ev, fde);
 100         }
 101
 102         return true;
 103 }
 104 #endif
 105
 106 static int std_event_loop_once(struct tevent_context *ev, const char *location)
 107 {
 108         void *glue_ptr = talloc_parent(ev->ops);
 109         struct std_event_glue *glue =
 110                 talloc_get_type_abort(glue_ptr,
 111                 struct std_event_glue);
 112         int ret;
 113
 114         ret = glue->epoll_ops->loop_once(ev, location);
 115         if (glue->epoll_ops != NULL) {
 116                 /* No fallback */
 117                 return ret;
 118         }
 119
 120         if (!glue->fallback_replay) {
 121                 /*
 122                  * The problem happened while modifying an event.
 123                  * An event handler was triggered in this case
 124                  * and there is no need to call loop_once() again.
 125                  */
 126                 return ret;
 127         }
 128
 129         return glue->poll_ops->loop_once(ev, location);
 130 }
 131
 132 static int std_event_loop_wait(struct tevent_context *ev, const char *location)
 133 {
 134         void *glue_ptr = talloc_parent(ev->ops);
 135         struct std_event_glue *glue =
 136                 talloc_get_type_abort(glue_ptr,
 137                 struct std_event_glue);
 138         int ret;
 139
 140         ret = glue->epoll_ops->loop_wait(ev, location);
 141         if (glue->epoll_ops != NULL) {
 142                 /* No fallback */
 143                 return ret;
 144         }
 145
 146         return glue->poll_ops->loop_wait(ev, location);
 147 }
 148 /*
 149   Initialize the epoll backend and allow it to call a
 150   switch function if epoll fails at runtime.
 151 */
 152 static int std_event_context_init(struct tevent_context *ev)
 153 {
 154         struct std_event_glue *glue;
 155         int ret;
 156
 157         /*
 158          * If this is the first initialization
 159          * we need to set up the allocated ops
 160          * pointers.
 161          */
 162
 163         if (ev->ops == &std_event_ops) {
 164                 glue = talloc_zero(ev, struct std_event_glue);
 165                 if (glue == NULL) {
 166                         return -1;
 167                 }
 168
 169                 glue->epoll_ops = tevent_find_ops_byname("epoll");
 170
 171                 glue->poll_ops = tevent_find_ops_byname("poll");
 172                 if (glue->poll_ops == NULL) {
 173                         return -1;
 174                 }
 175
 176                 /*
 177                  * Allocate space for our custom ops.
 178                  * Allocate as a child of our epoll_ops pointer
 179                  * so we can easily get to it using talloc_parent.
 180                  */
 181                 glue->glue_ops = talloc_zero(glue, struct tevent_ops);
 182                 if (glue->glue_ops == NULL) {
 183                         talloc_free(glue);
 184                         return -1;
 185                 }
 186
 187                 ev->ops = glue->glue_ops;
 188         } else {
 189                 void *glue_ptr = talloc_parent(ev->ops);
 190                 glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 191         }
 192
 193         if (glue->epoll_ops != NULL) {
 194                 /*
 195                  * Set custom_ops the same as epoll,
 196                  * except re-init using std_event_context_init()
 197                  * and use std_event_loop_once() to add the
 198                  * ability to fallback to a poll backend on
 199                  * epoll runtime error.
 200                  */
 201                 *glue->glue_ops = *glue->epoll_ops;
 202                 glue->glue_ops->context_init = std_event_context_init;
 203                 glue->glue_ops->loop_once = std_event_loop_once;
 204                 glue->glue_ops->loop_wait = std_event_loop_wait;
 205
 206                 ret = glue->epoll_ops->context_init(ev);
 207                 if (ret == -1) {
 208                         goto fallback;
 209                 }
 210 #ifdef HAVE_EPOLL
 211                 tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll);
 212 #endif
 213
 214                 return ret;
 215         }
 216
 217 fallback:
 218         glue->epoll_ops = NULL;
 219
 220         /*
 221          * Set custom_ops the same as poll.
 222          */
 223         *glue->glue_ops = *glue->poll_ops;
 224         glue->glue_ops->context_init = std_event_context_init;
 225
 226         return glue->poll_ops->context_init(ev);
 227 }
 228
 229 _PRIVATE_ bool tevent_standard_init(void)
 230 {
 231         return tevent_register_backend("standard", &std_event_ops);
 232 }