From: David Woodhouse <d...@amazon.co.uk>
Firing watches on the nodes that still exist is relatively easy; just
walk the tree and look at the nodes with refcount of one.
Firing watches on *deleted* nodes is more fun. We add 'modified_in_tx'
and 'deleted_in_tx' flags to each node. Nodes with those flags cannot
be shared, as they will always be unique to the transaction in which
they were created.
When xs_node_walk would need to *create* a node as scaffolding and it
encounters a deleted_in_tx node, it can resurrect it simply by clearing
its deleted_in_tx flag. If that node originally had any *data*, they're
gone, and the modified_in_tx flag will have been set when it was first
deleted.
We then attempt to send appropriate watches when the transaction is
committed, properly delete the deleted_in_tx nodes, and remove the
modified_in_tx flag from the others.
Signed-off-by: David Woodhouse <d...@amazon.co.uk>
Reviewed-by: Paul Durrant <p...@xen.org>
---
hw/i386/kvm/xenstore_impl.c | 151 ++++++++++++++++++++++-
tests/unit/test-xs-node.c | 231 +++++++++++++++++++++++++++++++++++-
2 files changed, 380 insertions(+), 2 deletions(-)
diff --git a/hw/i386/kvm/xenstore_impl.c b/hw/i386/kvm/xenstore_impl.c
index 0812e367b0..60f42f61d6 100644
--- a/hw/i386/kvm/xenstore_impl.c
+++ b/hw/i386/kvm/xenstore_impl.c
@@ -32,6 +32,8 @@ typedef struct XsNode {
GByteArray *content;
GHashTable *children;
uint64_t gencnt;
+ bool deleted_in_tx;
+ bool modified_in_tx;
#ifdef XS_NODE_UNIT_TEST
gchar *name; /* debug only */
#endif
@@ -153,6 +155,13 @@ static XsNode *xs_node_copy(XsNode *old)
XsNode *n = xs_node_new();
n->gencnt = old->gencnt;
+
+#ifdef XS_NODE_UNIT_TEST
+ if (n->name) {
+ n->name = g_strdup(old->name);
+ }
+#endif
+
if (old->children) {
n->children = g_hash_table_new_full(g_str_hash, g_str_equal, g_free,
(GDestroyNotify)xs_node_unref);
@@ -221,6 +230,9 @@ struct walk_op {
bool mutating;
bool create_dirs;
bool in_transaction;
+
+ /* Tracking during recursion so we know which is first. */
+ bool deleted_in_tx;
};
static void fire_watches(struct walk_op *op, bool parents)
@@ -277,6 +289,9 @@ static int xs_node_add_content(XsNode **n, struct walk_op
*op)
g_byte_array_unref((*n)->content);
}
(*n)->content = g_byte_array_ref(data);
+ if (op->tx_id != XBT_NULL) {
+ (*n)->modified_in_tx = true;
+ }
return 0;
}
@@ -333,10 +348,62 @@ static int node_rm_recurse(gpointer key, gpointer value,
gpointer user_data)
return this_inplace;
}
+static XsNode *xs_node_copy_deleted(XsNode *old, struct walk_op *op);
+static void copy_deleted_recurse(gpointer key, gpointer value,
+ gpointer user_data)
+{
+ struct walk_op *op = user_data;
+ GHashTable *siblings = op->op_opaque2;
+ XsNode *n = xs_node_copy_deleted(value, op);
+
+ /*
+ * Reinsert the deleted_in_tx copy of the node into the parent's
+ * 'children' hash table. Having stashed it from op->op_opaque2
+ * before the recursive call to xs_node_copy_deleted() scribbled
+ * over it.
+ */
+ g_hash_table_insert(siblings, g_strdup(key), n);
+}
+
+static XsNode *xs_node_copy_deleted(XsNode *old, struct walk_op *op)
+{
+ XsNode *n = xs_node_new();
+
+ n->gencnt = old->gencnt;
+
+#ifdef XS_NODE_UNIT_TEST
+ if (old->name) {
+ n->name = g_strdup(old->name);
+ }
+#endif
+
+ if (old->children) {
+ n->children = g_hash_table_new_full(g_str_hash, g_str_equal, g_free,
+ (GDestroyNotify)xs_node_unref);
+ op->op_opaque2 = n->children;
+ g_hash_table_foreach(old->children, copy_deleted_recurse, op);
+ }
+ n->deleted_in_tx = true;
+ /* If it gets resurrected we only fire a watch if it lost its content */
+ if (old->content) {
+ n->modified_in_tx = true;
+ }
+ op->new_nr_nodes--;
+ return n;
+}
+
static int xs_node_rm(XsNode **n, struct walk_op *op)
{
bool this_inplace = op->inplace;
+ if (op->tx_id != XBT_NULL) {
+ /* It's not trivial to do inplace handling for this one */
+ XsNode *old = *n;
+ *n = xs_node_copy_deleted(old, op);
+ xs_node_unref(old);
+ return 0;
+ }
+
/* Fire watches for, and count, nodes in the subtree which get deleted */
if ((*n)->children) {
g_hash_table_foreach_remove((*n)->children, node_rm_recurse, op);
@@ -408,6 +475,10 @@ static int xs_node_walk(XsNode **n, struct walk_op *op)
}
if (child) {
+ if (child->deleted_in_tx) {
+ assert(child->ref == 1);
+ /* Cannot actually set child->deleted_in_tx = false until later */
+ }
xs_node_ref(child);
/*
* Now we own it too. But if we can modify inplace, that's going to
@@ -475,6 +546,15 @@ static int xs_node_walk(XsNode **n, struct walk_op *op)
xs_node_unref(old);
}
+ /*
+ * If we resurrected a deleted_in_tx node, we can mark it as no longer
+ * deleted now that we know the overall operation has succeeded.
+ */
+ if (op->create_dirs && child && child->deleted_in_tx) {
+ op->new_nr_nodes++;
+ child->deleted_in_tx = false;
+ }
+
/*
* The child may be NULL here, for a remove operation. Either way,
* xs_node_add_child() will do the right thing and return a value
@@ -709,8 +789,69 @@ int xs_impl_transaction_start(XenstoreImplState *s,
unsigned int dom_id,
return 0;
}
+static gboolean tx_commit_walk(gpointer key, gpointer value,
+ gpointer user_data)
+{
+ struct walk_op *op = user_data;
+ int path_len = strlen(op->path);
+ int key_len = strlen(key);
+ bool fire_parents = true;
+ XsWatch *watch;
+ XsNode *n = value;
+
+ if (n->ref != 1) {
+ return false;
+ }
+
+ if (n->deleted_in_tx) {
+ /*
+ * We fire watches on our parents if we are the *first* node
+ * to be deleted (the topmost one). This matches the behaviour
+ * when deleting in the live tree.
+ */
+ fire_parents = !op->deleted_in_tx;
+
+ /* Only used on the way down so no need to clear it later */
+ op->deleted_in_tx = true;
+ }
+
+ assert(key_len + path_len + 2 <= sizeof(op->path));
+ op->path[path_len] = '/';
+ memcpy(op->path + path_len + 1, key, key_len + 1);
+
+ watch = g_hash_table_lookup(op->s->watches, op->path);
+ if (watch) {
+ op->watches = g_list_append(op->watches, watch);
+ }
+
+ if (n->children) {
+ g_hash_table_foreach_remove(n->children, tx_commit_walk, op);
+ }
+
+ if (watch) {
+ op->watches = g_list_remove(op->watches, watch);
+ }
+
+ /*
+ * Don't fire watches if this node was only copied because a
+ * descendent was changed. The modified_in_tx flag indicates the
+ * ones which were really changed.
+ */
+ if (n->modified_in_tx || n->deleted_in_tx) {
+ fire_watches(op, fire_parents);
+ n->modified_in_tx = false;
+ }
+ op->path[path_len] = '\0';
+
+ /* Deleted nodes really do get expunged when we commit */
+ return n->deleted_in_tx;
+}
+
static int transaction_commit(XenstoreImplState *s, XsTransaction *tx)
{
+ struct walk_op op;
+ XsNode **n;
+
if (s->root_tx != tx->base_tx) {
return EAGAIN;
}
@@ -720,10 +861,18 @@ static int transaction_commit(XenstoreImplState *s,
XsTransaction *tx)
s->root_tx = tx->tx_id;
s->nr_nodes = tx->nr_nodes;
+ init_walk_op(s, &op, XBT_NULL, tx->dom_id, "/", &n);
+ op.deleted_in_tx = false;
+ op.mutating = true;
+
/*
- * XX: Walk the new root and fire watches on any node which has a
+ * Walk the new root and fire watches on any node which has a
* refcount of one (which is therefore unique to this transaction).
*/
+ if (s->root->children) {
+ g_hash_table_foreach_remove(s->root->children, tx_commit_walk, &op);
+ }
+
return 0;
}
diff --git a/tests/unit/test-xs-node.c b/tests/unit/test-xs-node.c
index 3c3654550a..02c72baa62 100644
--- a/tests/unit/test-xs-node.c
+++ b/tests/unit/test-xs-node.c
@@ -347,7 +347,13 @@ static void do_test_xs_node_tx(bool fail, bool commit)
} else {
g_assert(!err);
}
- g_assert(!watches->len);
+ if (commit && !fail) {
+ g_assert(!strcmp(watches->str,
+ "some/relative/pathwatch"));
+ g_string_truncate(watches, 0);
+ } else {
+ g_assert(!watches->len);
+ }
g_assert(s->nr_nodes == 7);
err = xs_impl_unwatch(s, DOMID_GUEST, "some", "watch",
@@ -386,6 +392,226 @@ static void test_xs_node_tx_succeed(void)
do_test_xs_node_tx(false, true);
}
+static void test_xs_node_tx_rm(void)
+{
+ XenstoreImplState *s = setup();
+ GString *watches = g_string_new(NULL);
+ GByteArray *data = g_byte_array_new();
+ unsigned int tx_id = XBT_NULL;
+ int err;
+
+ g_assert(s);
+
+ /* Set a watch */
+ err = xs_impl_watch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+ g_assert(watches->len == strlen("somewatch"));
+ g_assert(!strcmp(watches->str, "somewatch"));
+ g_string_truncate(watches, 0);
+
+ /* Write something */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/deep/dark/relative/path",
+ "something");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+ g_assert(!strcmp(watches->str,
+ "some/deep/dark/relative/pathwatch"));
+ g_string_truncate(watches, 0);
+
+ /* Create a transaction */
+ err = xs_impl_transaction_start(s, DOMID_GUEST, &tx_id);
+ g_assert(!err);
+
+ /* Delete the tree in the transaction */
+ err = xs_impl_rm(s, DOMID_GUEST, tx_id, "some/deep/dark");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+ g_assert(!watches->len);
+
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL,
"some/deep/dark/relative/path",
+ data);
+ g_assert(!err);
+ g_assert(data->len == strlen("something"));
+ g_assert(!memcmp(data->data, "something", data->len));
+ g_byte_array_set_size(data, 0);
+
+ /* Commit the transaction */
+ err = xs_impl_transaction_end(s, DOMID_GUEST, tx_id, true);
+ g_assert(!err);
+ g_assert(s->nr_nodes == 6);
+
+ g_assert(!strcmp(watches->str, "some/deep/darkwatch"));
+ g_string_truncate(watches, 0);
+
+ /* Now the node is gone */
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL,
"some/deep/dark/relative/path",
+ data);
+ g_assert(err == ENOENT);
+ g_byte_array_unref(data);
+
+ err = xs_impl_unwatch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+
+ g_string_free(watches, true);
+ xs_impl_delete(s);
+}
+
+static void test_xs_node_tx_resurrect(void)
+{
+ XenstoreImplState *s = setup();
+ GString *watches = g_string_new(NULL);
+ GByteArray *data = g_byte_array_new();
+ unsigned int tx_id = XBT_NULL;
+ int err;
+
+ g_assert(s);
+
+ /* Write something */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/deep/dark/relative/path",
+ "something");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+
+ /* This node will be wiped and resurrected */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/deep/dark",
+ "foo");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+
+ /* Set a watch */
+ err = xs_impl_watch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+ g_assert(watches->len == strlen("somewatch"));
+ g_assert(!strcmp(watches->str, "somewatch"));
+ g_string_truncate(watches, 0);
+
+ /* Create a transaction */
+ err = xs_impl_transaction_start(s, DOMID_GUEST, &tx_id);
+ g_assert(!err);
+
+ /* Delete the tree in the transaction */
+ err = xs_impl_rm(s, DOMID_GUEST, tx_id, "some/deep");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+ g_assert(!watches->len);
+
+ /* Resurrect part of it */
+ err = write_str(s, DOMID_GUEST, tx_id, "some/deep/dark/different/path",
+ "something");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+
+ /* Commit the transaction */
+ err = xs_impl_transaction_end(s, DOMID_GUEST, tx_id, true);
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+
+ /* lost data */
+ g_assert(strstr(watches->str, "some/deep/dark/different/pathwatch"));
+ /* topmost deleted */
+ g_assert(strstr(watches->str, "some/deep/dark/relativewatch"));
+ /* lost data */
+ g_assert(strstr(watches->str, "some/deep/darkwatch"));
+
+ g_string_truncate(watches, 0);
+
+ /* Now the node is gone */
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL,
"some/deep/dark/relative/path",
+ data);
+ g_assert(err == ENOENT);
+ g_byte_array_unref(data);
+
+ err = xs_impl_unwatch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+
+ g_string_free(watches, true);
+ xs_impl_delete(s);
+}
+
+static void test_xs_node_tx_resurrect2(void)
+{
+ XenstoreImplState *s = setup();
+ GString *watches = g_string_new(NULL);
+ GByteArray *data = g_byte_array_new();
+ unsigned int tx_id = XBT_NULL;
+ int err;
+
+ g_assert(s);
+
+ /* Write something */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/deep/dark/relative/path",
+ "something");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 9);
+
+ /* Another node to remain shared */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/place/safe", "keepme");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 11);
+
+ /* This node will be wiped and resurrected */
+ err = write_str(s, DOMID_GUEST, XBT_NULL, "some/deep/dark",
+ "foo");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 11);
+
+ /* Set a watch */
+ err = xs_impl_watch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+ g_assert(watches->len == strlen("somewatch"));
+ g_assert(!strcmp(watches->str, "somewatch"));
+ g_string_truncate(watches, 0);
+
+ /* Create a transaction */
+ err = xs_impl_transaction_start(s, DOMID_GUEST, &tx_id);
+ g_assert(!err);
+
+ /* Delete the tree in the transaction */
+ err = xs_impl_rm(s, DOMID_GUEST, tx_id, "some/deep");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 11);
+ g_assert(!watches->len);
+
+ /* Resurrect part of it */
+ err = write_str(s, DOMID_GUEST, tx_id, "some/deep/dark/relative/path",
+ "something");
+ g_assert(!err);
+ g_assert(s->nr_nodes == 11);
+
+ /* Commit the transaction */
+ err = xs_impl_transaction_end(s, DOMID_GUEST, tx_id, true);
+ g_assert(!err);
+ g_assert(s->nr_nodes == 11);
+
+ /* lost data */
+ g_assert(strstr(watches->str, "some/deep/dark/relative/pathwatch"));
+ /* lost data */
+ g_assert(strstr(watches->str, "some/deep/darkwatch"));
+
+ g_string_truncate(watches, 0);
+
+ /* Now the node is gone */
+ err = xs_impl_read(s, DOMID_GUEST, XBT_NULL,
"some/deep/dark/relative/path",
+ data);
+ g_assert(!err);
+ g_assert(data->len == strlen("something"));
+ g_assert(!memcmp(data->data, "something", data->len));
+
+ g_byte_array_unref(data);
+
+ err = xs_impl_unwatch(s, DOMID_GUEST, "some", "watch",
+ watch_cb, watches);
+ g_assert(!err);
+
+ g_string_free(watches, true);
+ xs_impl_delete(s);
+}
+
int main(int argc, char **argv)
{
g_test_init(&argc, &argv, NULL);
@@ -395,6 +621,9 @@ int main(int argc, char **argv)
g_test_add_func("/xs_node/tx_abort", test_xs_node_tx_abort);
g_test_add_func("/xs_node/tx_fail", test_xs_node_tx_fail);
g_test_add_func("/xs_node/tx_succeed", test_xs_node_tx_succeed);
+ g_test_add_func("/xs_node/tx_rm", test_xs_node_tx_rm);
+ g_test_add_func("/xs_node/tx_resurrect", test_xs_node_tx_resurrect);
+ g_test_add_func("/xs_node/tx_resurrect2", test_xs_node_tx_resurrect2);
return g_test_run();
}
--
2.39.0
