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/*
Unix SMB/CIFS implementation.
main select loop and event handling
Copyright (C) Stefan Metzmacher 2013
Copyright (C) Jeremy Allison 2013
** NOTE! The following LGPL license applies to the tevent
** library. This does NOT imply that all of Samba is released
** under the LGPL
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
/*
This is SAMBA's default event loop code
- we try to use epoll if configure detected support for it
otherwise we use poll()
- if epoll is broken on the system or the kernel doesn't support it
at runtime we fallback to poll()
*/
#include "replace.h"
#include "tevent.h"
#include "tevent_util.h"
#include "tevent_internal.h"
struct std_event_glue {
const struct tevent_ops *epoll_ops;
const struct tevent_ops *poll_ops;
struct tevent_ops *glue_ops;
bool fallback_replay;
};
static int std_event_context_init(struct tevent_context *ev);
static const struct tevent_ops std_event_ops = {
.context_init = std_event_context_init,
};
/*
If this function gets called. epoll failed at runtime.
Move us to using poll instead. If we return false here,
caller should abort().
*/
static bool std_fallback_to_poll(struct tevent_context *ev, bool replay)
{
void *glue_ptr = talloc_parent(ev->ops);
struct std_event_glue *glue =
talloc_get_type_abort(glue_ptr,
struct std_event_glue);
int ret;
struct tevent_fd *fde;
struct tevent_fd *fde_next;
glue->fallback_replay = replay;
/* First switch all the ops to poll. */
glue->epoll_ops = NULL;
TALLOC_FREE(ev->additional_data);
/*
* Set custom_ops the same as poll.
*/
*glue->glue_ops = *glue->poll_ops;
glue->glue_ops->context_init = std_event_context_init;
/* Next initialize the poll backend. */
ret = glue->poll_ops->context_init(ev);
if (ret != 0) {
return false;
}
/*
* Now we have to change all the existing file descriptor
* events from the epoll backend to the poll backend.
*/
for (fde = ev->fd_events; fde; fde = fde_next) {
/*
* We must remove this fde off the ev->fd_events list.
*/
fde_next = fde->next;
/* Remove from the ev->fd_events list. */
DLIST_REMOVE(ev->fd_events, fde);
/* Re-add this event as a poll backend event. */
tevent_poll_event_add_fd_internal(ev, fde);
}
return true;
}
static int std_event_loop_once(struct tevent_context *ev, const char *location)
{
void *glue_ptr = talloc_parent(ev->ops);
struct std_event_glue *glue =
talloc_get_type_abort(glue_ptr,
struct std_event_glue);
int ret;
ret = glue->epoll_ops->loop_once(ev, location);
if (glue->epoll_ops != NULL) {
/* No fallback */
return ret;
}
if (!glue->fallback_replay) {
/*
* The problem happened while modifying an event.
* An event handler was triggered in this case
* and there is no need to call loop_once() again.
*/
return ret;
}
return glue->poll_ops->loop_once(ev, location);
}
/*
Initialize the epoll backend and allow it to call a
switch function if epoll fails at runtime.
*/
static int std_event_context_init(struct tevent_context *ev)
{
struct std_event_glue *glue;
int ret;
/*
* If this is the first initialization
* we need to set up the allocated ops
* pointers.
*/
if (ev->ops == &std_event_ops) {
glue = talloc_zero(ev, struct std_event_glue);
if (glue == NULL) {
return -1;
}
glue->epoll_ops = tevent_find_ops_byname("epoll");
glue->poll_ops = tevent_find_ops_byname("poll");
if (glue->poll_ops == NULL) {
return -1;
}
/*
* Allocate space for our custom ops.
* Allocate as a child of our epoll_ops pointer
* so we can easily get to it using talloc_parent.
*/
glue->glue_ops = talloc_zero(glue, struct tevent_ops);
if (glue->glue_ops == NULL) {
talloc_free(glue);
return -1;
}
ev->ops = glue->glue_ops;
} else {
void *glue_ptr = talloc_parent(ev->ops);
glue = talloc_get_type_abort(glue_ptr, struct std_event_glue);
}
if (glue->epoll_ops != NULL) {
/*
* Set custom_ops the same as epoll,
* except re-init using std_event_context_init()
* and use std_event_loop_once() to add the
* ability to fallback to a poll backend on
* epoll runtime error.
*/
*glue->glue_ops = *glue->epoll_ops;
glue->glue_ops->context_init = std_event_context_init;
glue->glue_ops->loop_once = std_event_loop_once;
ret = glue->epoll_ops->context_init(ev);
if (ret == -1) {
goto fallback;
}
#ifdef HAVE_EPOLL
if (!tevent_epoll_set_panic_fallback(ev, std_fallback_to_poll)) {
TALLOC_FREE(ev->additional_data);
goto fallback;
}
#endif
return ret;
}
fallback:
glue->epoll_ops = NULL;
/*
* Set custom_ops the same as poll.
*/
*glue->glue_ops = *glue->poll_ops;
glue->glue_ops->context_init = std_event_context_init;
return glue->poll_ops->context_init(ev);
}
_PRIVATE_ bool tevent_standard_init(void)
{
return tevent_register_backend("standard", &std_event_ops);
}
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