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 /*
 131   Initialize the epoll backend and allow it to call a
 132   switch function if epoll fails at runtime.
 133 */
 134 static int std_event_context_init(struct tevent_context *ev)
 135 {
 136         struct std_event_glue *glue;
 137         int ret;
 138
 139         /*
 140          * If this is the first initialization
 141          * we need to set up the allocated ops
 142          * pointers.
 143          */
 144
 145         if (ev->ops == &std_event_ops) {
 146                 glue = talloc_zero(ev, struct std_event_glue);
 147                 if (glue == NULL) {
 148                         return -1;
 149                 }
 150
 151                 glue->epoll_ops = tevent_find_ops_byname("epoll");
 152
 153                 glue->poll_ops = tevent_find_ops_byname("poll");
 154                 if (glue->poll_ops == NULL) {
 155                         return -1;
 156                 }
 157
 158                 /*
 159                  * Allocate space for our custom ops.
 160                  * Allocate as a child of our epoll_ops pointer
 161                  * so we can easily get to it using talloc_parent.
 162                  */
 163                 glue->glue_ops = talloc_zero(glue, struct tevent_ops);
 164                 if (glue->glue_ops == NULL) {
 165                         talloc_free(glue);
 166                         return -1;
 167                 }
 168
 169                 ev->ops = glue->glue_ops;
 170         } else {
 171                 void *glue_ptr = talloc_parent(ev->ops);
 172                 glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
 173         }
 174
 175         if (glue->epoll_ops != NULL) {
 176                 /*
 177                  * Set custom_ops the same as epoll,
 178                  * except re-init using std_event_context_init()
 179                  * and use std_event_loop_once() to add the
 180                  * ability to fallback to a poll backend on
 181                  * epoll runtime error.
 182                  */
 183                 *glue->glue_ops = *glue->epoll_ops;
 184                 glue->glue_ops->context_init = std_event_context_init;
 185                 glue->glue_ops->loop_once = std_event_loop_once;
 186
 187                 ret = glue->epoll_ops->context_init(ev);
 188                 if (ret == -1) {
 189                         goto fallback;
 190                 }
 191 #ifdef HAVE_EPOLL
 192                 if (!tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll)) {
 193                         TALLOC_FREE(ev->additional_data);
 194                         goto fallback;
 195                 }
 196 #endif
 197
 198                 return ret;
 199         }
 200
 201 fallback:
 202         glue->epoll_ops = NULL;
 203
 204         /*
 205          * Set custom_ops the same as poll.
 206          */
 207         *glue->glue_ops = *glue->poll_ops;
 208         glue->glue_ops->context_init = std_event_context_init;
 209
 210         return glue->poll_ops->context_init(ev);
 211 }
 212
 213 _PRIVATE_ bool tevent_standard_init(void)
 214 {
 215         return tevent_register_backend("standard", &std_event_ops);
 216 }