[PATCH v11 14/27] tools/xenstore: allow live update only with no transaction active

[Juergen Gross <jgross@xxxxxxxx>]

In order to simplify live update state dumping only allow live update
to happen when no transaction is active.

A timeout is used to detect guests which have a transaction active for
longer periods of time. In case such a guest is detected when trying
to do a live update it will be reported and the update will fail.

The admin can then either use a longer timeout, or use the force flag
to just ignore the transactions of such a guest, or kill the guest
before retrying.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V11:
- reworked timeout logic to be handled in daemon (Edwin Torok)
---
 tools/xenstore/xenstored_control.c     | 29 ++++++++++++++++++++++++--
 tools/xenstore/xenstored_core.h        |  1 +
 tools/xenstore/xenstored_transaction.c |  5 +++++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/tools/xenstore/xenstored_control.c 
b/tools/xenstore/xenstored_control.c
index 5193c55781..0c3dc14fb7 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c
@@ -312,12 +312,37 @@ static const char *lu_arch(const void *ctx, struct 
connection *conn,
 
 static bool lu_check_lu_allowed(void)
 {
-       return true;
+       struct connection *conn;
+       time_t now = time(NULL);
+       unsigned int ta_total = 0, ta_long = 0;
+
+       list_for_each_entry(conn, &connections, list) {
+               if (conn->ta_start_time) {
+                       ta_total++;
+                       if (conn->ta_start_time - now >= lu_status->timeout)
+                               ta_long++;
+               }
+       }
+
+       return ta_total ? (lu_status->force && ta_long == ta_total) : true;
 }
 
 static const char *lu_reject_reason(const void *ctx)
 {
-       return "BUSY";
+       char *ret = NULL;
+       struct connection *conn;
+       time_t now = time(NULL);
+
+       list_for_each_entry(conn, &connections, list) {
+               if (conn->ta_start_time - now >= lu_status->timeout) {
+                       ret = talloc_asprintf(ctx, "%s\nDomain %u: %ld s",
+                                             ret ? : "Domains with long 
running transactions:",
+                                             conn->id,
+                                             conn->ta_start_time - now);
+               }
+       }
+
+       return ret ? (const char *)ret : "Overlapping transactions";
 }
 
 static const char *lu_dump_state(const void *ctx, struct connection *conn)
diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
index d5cdf17160..db70f61f0d 100644
--- a/tools/xenstore/xenstored_core.h
+++ b/tools/xenstore/xenstored_core.h
@@ -107,6 +107,7 @@ struct connection
        struct list_head transaction_list;
        uint32_t next_transaction_id;
        unsigned int transaction_started;
+       time_t ta_start_time;
 
        /* List of delayed requests. */
        struct list_head delayed;
diff --git a/tools/xenstore/xenstored_transaction.c 
b/tools/xenstore/xenstored_transaction.c
index 52355f4ed8..cd07fb0f21 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -473,6 +473,8 @@ int do_transaction_start(struct connection *conn, struct 
buffered_data *in)
        list_add_tail(&trans->list, &conn->transaction_list);
        talloc_steal(conn, trans);
        talloc_set_destructor(trans, destroy_transaction);
+       if (!conn->transaction_started)
+               conn->ta_start_time = time(NULL);
        conn->transaction_started++;
        wrl_ntransactions++;
 
@@ -511,6 +513,8 @@ int do_transaction_end(struct connection *conn, struct 
buffered_data *in)
        conn->transaction = NULL;
        list_del(&trans->list);
        conn->transaction_started--;
+       if (!conn->transaction_started)
+               conn->ta_start_time = 0;
 
        /* Attach transaction to in for auto-cleanup */
        talloc_steal(in, trans);
@@ -589,6 +593,7 @@ void conn_delete_all_transactions(struct connection *conn)
        assert(conn->transaction == NULL);
 
        conn->transaction_started = 0;
+       conn->ta_start_time = 0;
 }
 
 int check_transactions(struct hashtable *hash)
-- 
2.26.2