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
  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                 bool ok;
  90
  91                 /* Re-add this event as a poll backend event. */
  92                 ok = tevent_poll_event_add_fd_internal(ev, fde);
  93                 if (!ok) {
  94                         return false;
  95                 }
  96         }
  97
  98         return true;
  99 }
 100 #endif
 101
 102 static int std_event_loop_once(struct tevent_context *ev, const char *location)
 103 {
 104         void *glue_ptr = talloc_parent(ev->ops);
 105         struct std_event_glue *glue =
 106                 talloc_get_type_abort(glue_ptr,
 107                 struct std_event_glue);
 108         int ret;
 109
 110         ret = glue->epoll_ops->loop_once(ev, location);
 111         /*
 112          * If the above hasn't panicked due to an epoll interface failure,
 113          * std_fallback_to_poll() wasn't called, and hasn't cleared epoll_ops to
 114          * signify fallback to poll_ops.
 115          */
 116         if (glue->epoll_ops != NULL) {
 117                 /* No fallback */
 118                 return ret;
 119         }
 120
 121         if (!glue->fallback_replay) {
 122                 /*
 123                  * The problem happened while modifying an event.
 124                  * An event handler was triggered in this case
 125                  * and there is no need to call loop_once() again.
 126                  */
 127                 return ret;
 128         }
 129
 130         return glue->poll_ops->loop_once(ev, location);
 131 }
 132
 133 static int std_event_loop_wait(struct tevent_context *ev, const char *location)
 134 {
 135         void *glue_ptr = talloc_parent(ev->ops);
 136         struct std_event_glue *glue =
 137                 talloc_get_type_abort(glue_ptr,
 138                 struct std_event_glue);
 139         int ret;
 140
 141         ret = glue->epoll_ops->loop_wait(ev, location);
 142         /*
 143          * If the above hasn't panicked due to an epoll interface failure,
 144          * std_fallback_to_poll() wasn't called, and hasn't cleared epoll_ops to
 145          * signify fallback to poll_ops.
 146          */
 147         if (glue->epoll_ops != NULL) {
 148                 /* No fallback */
 149                 return ret;
 150         }
 151
 152         return glue->poll_ops->loop_wait(ev, location);
 153 }
 154 /*
 155   Initialize the epoll backend and allow it to call a
 156   switch function if epoll fails at runtime.
 157 */
 158 static int std_event_context_init(struct tevent_context *ev)
 159 {
 160         struct std_event_glue *glue;
 161         int ret;
 162
 163         /*
 164          * If this is the first initialization
 165          * we need to set up the allocated ops
 166          * pointers.
 167          */
 168
 169         if (ev->ops == &std_event_ops) {
 170                 glue = talloc_zero(ev, struct std_event_glue);
 171                 if (glue == NULL) {
 172                         return -1;
 173                 }
 174
 175                 glue->epoll_ops = tevent_find_ops_byname("epoll");
 176
 177                 glue->poll_ops = tevent_find_ops_byname("poll");
 178                 if (glue->poll_ops == NULL) {
 179                         return -1;
 180                 }
 181
 182                 /*
 183                  * Allocate space for our custom ops.
 184                  * Allocate as a child of our epoll_ops pointer
 185                  * so we can easily get to it using talloc_parent.
 186                  */
 187                 glue->glue_ops = talloc_zero(glue, struct tevent_ops);
 188                 if (glue->glue_ops == NULL) {
 189                         talloc_free(glue);
 190                         return -1;
 191                 }
 192
 193                 ev->ops = glue->glue_ops;
 194         } else {
 195                 void *glue_ptr = talloc_parent(ev->ops);
 196                 glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 197         }
 198
 199         if (glue->epoll_ops != NULL) {
 200                 /*
 201                  * Set custom_ops the same as epoll,
 202                  * except re-init using std_event_context_init()
 203                  * and use std_event_loop_once() to add the
 204                  * ability to fallback to a poll backend on
 205                  * epoll runtime error.
 206                  */
 207                 *glue->glue_ops = *glue->epoll_ops;
 208                 glue->glue_ops->context_init = std_event_context_init;
 209                 glue->glue_ops->loop_once = std_event_loop_once;
 210                 glue->glue_ops->loop_wait = std_event_loop_wait;
 211
 212                 ret = glue->epoll_ops->context_init(ev);
 213                 if (ret == -1) {
 214                         goto fallback;
 215                 }
 216 #ifdef HAVE_EPOLL
 217                 tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll);
 218 #endif
 219
 220                 return ret;
 221         }
 222
 223 fallback:
 224         glue->epoll_ops = NULL;
 225
 226         /*
 227          * Set custom_ops the same as poll.
 228          */
 229         *glue->glue_ops = *glue->poll_ops;
 230         glue->glue_ops->context_init = std_event_context_init;
 231
 232         return glue->poll_ops->context_init(ev);
 233 }
 234
 235 _PRIVATE_ bool tevent_standard_init(void)
 236 {
 237         return tevent_register_backend("standard", &std_event_ops);
 238 }