[MINOR] add back-references to sessions for later use by a dumper.

This is the first step in implementing a session dump tool.
A session dump will need restart points. It will be necessary for
it to get references to sessions which can be moved when the session
dies.

The principle is not that complex : when a session ends, it looks for
any potential back-references. If it finds any, then it moves them to
the next session in the list. The dump function will of course have
to restart from that new point.

include/types/session.h

@@ -153,6 +153,7 @@ enum {
  */
 struct session {
 	struct list list;			/* position in global sessions list */
+	struct list back_refs;			/* list of users tracking this session */
 	struct task *task;			/* the task associated with this session */
 	/* application specific below */
 	struct listener *listener;		/* the listener by which the request arrived */

src/client.c

@@ -66,6 +66,7 @@ int event_accept(int fd) {
 	struct session *s;
 	struct http_txn *txn;
 	struct task *t;
+	struct bref *bref, *back;
 	int cfd;
 	int max_accept = global.tune.maxaccept;
 
@@ -108,6 +109,7 @@ int event_accept(int fd) {
 		}
 
 		LIST_ADDQ(&sessions, &s->list);
+		LIST_INIT(&s->back_refs);
 
 		s->flags = 0;
 		s->term_trace = 0;
@@ -464,6 +466,11 @@ int event_accept(int fd) {
  out_free_task:
 	pool_free2(pool2_task, t);
  out_free_session:
+	list_for_each_entry_safe(bref, back, &s->back_refs, users) {
+		LIST_DEL(&bref->users);
+		LIST_ADDQ(&LIST_ELEM(s->list.n, struct session *, list)->back_refs, &bref->users);
+		bref->ref = s->list.n;
+	}
 	LIST_DEL(&s->list);
 	pool_free2(pool2_session, s);
  out_close:

src/proto_uxst.c

@@ -360,6 +360,7 @@ int uxst_event_accept(int fd) {
 	struct listener *l = fdtab[fd].owner;
 	struct session *s;
 	struct task *t;
+	struct bref *bref, *back;
 	int cfd;
 	int max_accept;
 
@@ -409,6 +410,7 @@ int uxst_event_accept(int fd) {
 		}
 
 		LIST_ADDQ(&sessions, &s->list);
+		LIST_INIT(&s->back_refs);
 
 		s->flags = 0;
 		s->term_trace = 0;
@@ -545,6 +547,11 @@ int uxst_event_accept(int fd) {
  out_free_task:
 	pool_free2(pool2_task, t);
  out_free_session:
+	list_for_each_entry_safe(bref, back, &s->back_refs, users) {
+		LIST_DEL(&bref->users);
+		LIST_ADDQ(&LIST_ELEM(s->list.n, struct session *, list)->back_refs, &bref->users);
+		bref->ref = s->list.n;
+	}
 	LIST_DEL(&s->list);
 	pool_free2(pool2_session, s);
  out_close:

src/session.c

@@ -42,6 +42,7 @@ void session_free(struct session *s)
 {
 	struct http_txn *txn = &s->txn;
 	struct proxy *fe = s->fe;
+	struct bref *bref, *back;
 
 	if (s->pend_pos)
 		pendconn_free(s->pend_pos);
@@ -82,6 +83,12 @@ void session_free(struct session *s)
 	pool_free2(pool2_requri, txn->uri);
 	pool_free2(pool2_capture, txn->cli_cookie);
 	pool_free2(pool2_capture, txn->srv_cookie);
+
+	list_for_each_entry_safe(bref, back, &s->back_refs, users) {
+		LIST_DEL(&bref->users);
+		LIST_ADDQ(&LIST_ELEM(s->list.n, struct session *, list)->back_refs, &bref->users);
+		bref->ref = s->list.n;
+	}
 	LIST_DEL(&s->list);
 	pool_free2(pool2_session, s);