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From e26d6f4d1b389b859fb5a6570421e80e0213f92b Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Tue, 13 Sep 2022 07:35:07 +0200
Subject: [PATCH 48/87] tools/xenstore: reduce number of watch events
When removing a watched node outside of a transaction, two watch events
are being produced instead of just a single one.
When finalizing a transaction watch events can be generated for each
node which is being modified, even if outside a transaction such
modifications might not have resulted in a watch event.
This happens e.g.:
- for nodes which are only modified due to added/removed child entries
- for nodes being removed or created implicitly (e.g. creation of a/b/c
is implicitly creating a/b, resulting in watch events for a, a/b and
a/b/c instead of a/b/c only)
Avoid these additional watch events, in order to reduce the needed
memory inside Xenstore for queueing them.
This is being achieved by adding event flags to struct accessed_node
specifying whether an event should be triggered, and whether it should
be an exact match of the modified path. Both flags can be set from
fire_watches() instead of implying them only.
This is part of XSA-326.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
(cherry picked from commit 3a96013a3e17baa07410b1b9776225d1d9a74297)
---
tools/xenstore/xenstored_core.c | 19 ++++++------
tools/xenstore/xenstored_transaction.c | 41 +++++++++++++++++++++-----
tools/xenstore/xenstored_transaction.h | 3 ++
tools/xenstore/xenstored_watch.c | 7 +++--
4 files changed, 51 insertions(+), 19 deletions(-)
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 527a1ebdeded..bf2243873901 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -1295,7 +1295,7 @@ static void delete_child(struct connection *conn,
}
static int delete_node(struct connection *conn, const void *ctx,
- struct node *parent, struct node *node)
+ struct node *parent, struct node *node, bool watch_exact)
{
char *name;
@@ -1307,7 +1307,7 @@ static int delete_node(struct connection *conn, const void *ctx,
node->children);
child = name ? read_node(conn, node, name) : NULL;
if (child) {
- if (delete_node(conn, ctx, node, child))
+ if (delete_node(conn, ctx, node, child, true))
return errno;
} else {
trace("delete_node: Error deleting child '%s/%s'!\n",
@@ -1319,7 +1319,12 @@ static int delete_node(struct connection *conn, const void *ctx,
talloc_free(name);
}
- fire_watches(conn, ctx, node->name, node, true, NULL);
+ /*
+ * Fire the watches now, when we can still see the node permissions.
+ * This fine as we are single threaded and the next possible read will
+ * be handled only after the node has been really removed.
+ */
+ fire_watches(conn, ctx, node->name, node, watch_exact, NULL);
delete_node_single(conn, node);
delete_child(conn, parent, basename(node->name));
talloc_free(node);
@@ -1345,13 +1350,7 @@ static int _rm(struct connection *conn, const void *ctx, struct node *node,
return (errno == ENOMEM) ? ENOMEM : EINVAL;
node->parent = parent;
- /*
- * Fire the watches now, when we can still see the node permissions.
- * This fine as we are single threaded and the next possible read will
- * be handled only after the node has been really removed.
- */
- fire_watches(conn, ctx, name, node, false, NULL);
- return delete_node(conn, ctx, parent, node);
+ return delete_node(conn, ctx, parent, node, false);
}
diff --git a/tools/xenstore/xenstored_transaction.c b/tools/xenstore/xenstored_transaction.c
index faf6c930e42a..54432907fc76 100644
--- a/tools/xenstore/xenstored_transaction.c
+++ b/tools/xenstore/xenstored_transaction.c
@@ -130,6 +130,10 @@ struct accessed_node
/* Transaction node in data base? */
bool ta_node;
+
+ /* Watch event flags. */
+ bool fire_watch;
+ bool watch_exact;
};
struct changed_domain
@@ -323,6 +327,29 @@ err:
return ret;
}
+/*
+ * A watch event should be fired for a node modified inside a transaction.
+ * Set the corresponding information. A non-exact event is replacing an exact
+ * one, but not the other way round.
+ */
+void queue_watches(struct connection *conn, const char *name, bool watch_exact)
+{
+ struct accessed_node *i;
+
+ i = find_accessed_node(conn->transaction, name);
+ if (!i) {
+ conn->transaction->fail = true;
+ return;
+ }
+
+ if (!i->fire_watch) {
+ i->fire_watch = true;
+ i->watch_exact = watch_exact;
+ } else if (!watch_exact) {
+ i->watch_exact = false;
+ }
+}
+
/*
* Finalize transaction:
* Walk through accessed nodes and check generation against global data.
@@ -377,15 +404,15 @@ static int finalize_transaction(struct connection *conn,
ret = tdb_store(tdb_ctx, key, data,
TDB_REPLACE);
talloc_free(data.dptr);
- if (ret)
- goto err;
- fire_watches(conn, trans, i->node, NULL, false,
- i->perms.p ? &i->perms : NULL);
} else {
- fire_watches(conn, trans, i->node, NULL, false,
+ ret = tdb_delete(tdb_ctx, key);
+ }
+ if (ret)
+ goto err;
+ if (i->fire_watch) {
+ fire_watches(conn, trans, i->node, NULL,
+ i->watch_exact,
i->perms.p ? &i->perms : NULL);
- if (tdb_delete(tdb_ctx, key))
- goto err;
}
}
diff --git a/tools/xenstore/xenstored_transaction.h b/tools/xenstore/xenstored_transaction.h
index 14062730e3c9..0093cac807e3 100644
--- a/tools/xenstore/xenstored_transaction.h
+++ b/tools/xenstore/xenstored_transaction.h
@@ -42,6 +42,9 @@ void transaction_entry_dec(struct transaction *trans, unsigned int domid);
int access_node(struct connection *conn, struct node *node,
enum node_access_type type, TDB_DATA *key);
+/* Queue watches for a modified node. */
+void queue_watches(struct connection *conn, const char *name, bool watch_exact);
+
/* Prepend the transaction to name if appropriate. */
int transaction_prepend(struct connection *conn, const char *name,
TDB_DATA *key);
diff --git a/tools/xenstore/xenstored_watch.c b/tools/xenstore/xenstored_watch.c
index 99a2c266b28a..205d9d8ea116 100644
--- a/tools/xenstore/xenstored_watch.c
+++ b/tools/xenstore/xenstored_watch.c
@@ -29,6 +29,7 @@
#include "xenstore_lib.h"
#include "utils.h"
#include "xenstored_domain.h"
+#include "xenstored_transaction.h"
extern int quota_nb_watch_per_domain;
@@ -143,9 +144,11 @@ void fire_watches(struct connection *conn, const void *ctx, const char *name,
struct connection *i;
struct watch *watch;
- /* During transactions, don't fire watches. */
- if (conn && conn->transaction)
+ /* During transactions, don't fire watches, but queue them. */
+ if (conn && conn->transaction) {
+ queue_watches(conn, name, exact);
return;
+ }
/* Create an event for each watch. */
list_for_each_entry(i, &connections, list) {
--
2.37.4
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