[CRIU] [PATCH v4 14/33] files: Implement {set,wait}_fds_event()

[Kirill Tkhai]

The idea is symilar to kernel's wake_up() and wait_event().
One task needs some event. It checks the event has not
happened yet (fle hasn't received, unix peer hasn't bound, etc)
and calls get_fds_event(). Other task makes the event
(sends a fle, binds the peer to a name, etc) and calls set_fds_event().

So, while there is no an event, the first task is sleeping,
and the second wakes it up later:

Task A:      if (!socket_bound)
                     wait_fds_event(); /* sleep */

Task B:      bind_socket();
             set_fds_event();         /* wake up */

v2: Do not wait for foreign transport sock is ready,
as it's guarantied by we create it before CR_STATE_FORKING

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 criu/files.c          |   34 ++++++++++++++++++++++++++++++++++
 criu/include/files.h  |    2 ++
 include/common/lock.h |    5 +++++
 3 files changed, 41 insertions(+)

diff --git a/criu/files.c b/criu/files.c
index 4039803..69a43c6 100644
--- a/criu/files.c
+++ b/criu/files.c
@@ -1631,3 +1631,37 @@ int open_transport_socket(void)
 
 	return 0;
 }
+
+int set_fds_event(pid_t virt)
+{
+	struct pstree_item *item;
+	int old, st;
+
+	item = pstree_item_by_virt(virt);
+	BUG_ON(!item);
+
+	/* Set FDS_EVENT and wake up if need */
+	do {
+		old = futex_get(&item->task_st);
+		if (old & FDS_EVENT)
+			break;
+		st = atomic_cmpxchg(&item->task_st.raw, old, old | FDS_EVENT);
+	} while (st != old);
+
+	if (!(old & FDS_EVENT))
+		futex_wake(&item->task_st);
+	return 0;
+}
+
+int wait_fds_event(void)
+{
+	int old, st;
+
+	futex_wait_if_cond(&current->task_st, FDS_EVENT, &);
+	do {
+		old = futex_get(&current->task_st);
+		st = atomic_cmpxchg(&current->task_st.raw, old, old & ~FDS_EVENT);
+	} while (st != old);
+
+	return 0;
+}
diff --git a/criu/include/files.h b/criu/include/files.h
index 5719004..7fdb3cf 100644
--- a/criu/include/files.h
+++ b/criu/include/files.h
@@ -193,5 +193,7 @@ int dup_fle(struct pstree_item *task, struct fdinfo_list_entry *ple,
 	    int fd, unsigned flags);
 
 extern int open_transport_socket(void);
+extern int set_fds_event(pid_t virt);
+extern int wait_fds_event(void);
 
 #endif /* __CR_FILES_H__ */
diff --git a/include/common/lock.h b/include/common/lock.h
index afc0f96..2261cf9 100644
--- a/include/common/lock.h
+++ b/include/common/lock.h
@@ -78,6 +78,11 @@ static inline void futex_set_and_wake(futex_t *f, uint32_t v)
 	LOCK_BUG_ON(sys_futex((uint32_t *)&f->raw.counter, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
 }
 
+static inline void futex_wake(futex_t *f)
+{
+	LOCK_BUG_ON(sys_futex((uint32_t *)&f->raw.counter, FUTEX_WAKE, INT_MAX, NULL, NULL, 0) < 0);
+}
+
 /* Mark futex @f as wait abort needed and wake up all waiters */
 static inline void futex_abort_and_wake(futex_t *f)
 {