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         TALLOC_FREE(ev->additional_data);
  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
 105 static int std_event_loop_once(struct tevent_context *ev, const char *location)
 106 {
 107         void *glue_ptr = talloc_parent(ev->ops);
 108         struct std_event_glue *glue =
 109                 talloc_get_type_abort(glue_ptr,
 110                 struct std_event_glue);
 111         int ret;
 112
 113         ret = glue->epoll_ops->loop_once(ev, location);
 114         if (glue->epoll_ops != NULL) {
 115                 /* No fallback */
 116                 return ret;
 117         }
 118
 119         if (!glue->fallback_replay) {
 120                 /*
 121                  * The problem happened while modifying an event.
 122                  * An event handler was triggered in this case
 123                  * and there is no need to call loop_once() again.
 124                  */
 125                 return ret;
 126         }
 127
 128         return glue->poll_ops->loop_once(ev, location);
 129 }
 130
 131 /*
 132   Initialize the epoll backend and allow it to call a
 133   switch function if epoll fails at runtime.
 134 */
 135 static int std_event_context_init(struct tevent_context *ev)
 136 {
 137         struct std_event_glue *glue;
 138         int ret;
 139
 140         /*
 141          * If this is the first initialization
 142          * we need to set up the allocated ops
 143          * pointers.
 144          */
 145
 146         if (ev->ops == &std_event_ops) {
 147                 glue = talloc_zero(ev, struct std_event_glue);
 148                 if (glue == NULL) {
 149                         return -1;
 150                 }
 151
 152                 glue->epoll_ops = tevent_find_ops_byname("epoll");
 153
 154                 glue->poll_ops = tevent_find_ops_byname("poll");
 155                 if (glue->poll_ops == NULL) {
 156                         return -1;
 157                 }
 158
 159                 /*
 160                  * Allocate space for our custom ops.
 161                  * Allocate as a child of our epoll_ops pointer
 162                  * so we can easily get to it using talloc_parent.
 163                  */
 164                 glue->glue_ops = talloc_zero(glue, struct tevent_ops);
 165                 if (glue->glue_ops == NULL) {
 166                         talloc_free(glue);
 167                         return -1;
 168                 }
 169
 170                 ev->ops = glue->glue_ops;
 171         } else {
 172                 void *glue_ptr = talloc_parent(ev->ops);
 173                 glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 174         }
 175
 176         if (glue->epoll_ops != NULL) {
 177                 /*
 178                  * Set custom_ops the same as epoll,
 179                  * except re-init using std_event_context_init()
 180                  * and use std_event_loop_once() to add the
 181                  * ability to fallback to a poll backend on
 182                  * epoll runtime error.
 183                  */
 184                 *glue->glue_ops = *glue->epoll_ops;
 185                 glue->glue_ops->context_init = std_event_context_init;
 186                 glue->glue_ops->loop_once = std_event_loop_once;
 187
 188                 ret = glue->epoll_ops->context_init(ev);
 189                 if (ret == -1) {
 190                         goto fallback;
 191                 }
 192 #ifdef HAVE_EPOLL
 193                 if (!tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll)) {
 194                         TALLOC_FREE(ev->additional_data);
 195                         goto fallback;
 196                 }
 197 #endif
 198
 199                 return ret;
 200         }
 201
 202 fallback:
 203         glue->epoll_ops = NULL;
 204
 205         /*
 206          * Set custom_ops the same as poll.
 207          */
 208         *glue->glue_ops = *glue->poll_ops;
 209         glue->glue_ops->context_init = std_event_context_init;
 210
 211         return glue->poll_ops->context_init(ev);
 212 }
 213
 214 _PRIVATE_ bool tevent_standard_init(void)
 215 {
 216         return tevent_register_backend("standard", &std_event_ops);
 217 }