By verifying that singleton tables (that is, tables that should have exactly
one row) are empty when they emit transactions that insert into them,
ovs-vsctl and similar tools tolerate initialization races, where more than one
client at a time tries to initialize a singleton table.
The upshot is that if you create a database and then run multiple ovs-vsctl
(etc.) commands against it in parallel (without first initializing it
serially), then without this patch sometimes you will sometimes get failures
but this patch avoids them.
Signed-off-by: Ben Pfaff <b...@ovn.org>
---
lib/ovsdb-idl-provider.h | 1 +
lib/ovsdb-idl.c | 24 ++++++++++++++++++++----
ovsdb/ovsdb-idlc.in | 8 ++++++--
3 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/lib/ovsdb-idl-provider.h b/lib/ovsdb-idl-provider.h
index d15ab1db58a6..b0ebed44f83a 100644
--- a/lib/ovsdb-idl-provider.h
+++ b/lib/ovsdb-idl-provider.h
@@ -101,6 +101,7 @@ struct ovsdb_idl_column {
struct ovsdb_idl_table_class {
char *name;
bool is_root;
+ bool is_singleton;
const struct ovsdb_idl_column *columns;
size_t n_columns;
size_t allocation_size;
diff --git a/lib/ovsdb-idl.c b/lib/ovsdb-idl.c
index 12009f568575..e2f9af7f61d4 100644
--- a/lib/ovsdb-idl.c
+++ b/lib/ovsdb-idl.c
@@ -3538,12 +3538,28 @@ ovsdb_idl_txn_commit(struct ovsdb_idl_txn *txn)
}
} else if (row->old_datum != row->new_datum) {
struct json *row_json;
- struct json *op;
size_t idx;
- op = json_object_create();
- json_object_put_string(op, "op", row->old_datum ? "update"
- : "insert");
+ if (!row->old_datum && class->is_singleton) {
+ /* We're inserting a row into a table that allows only a
+ * single row. (This is a fairly common OVSDB pattern for
+ * storing global data.) Verify that the table is empty
+ * before inserting the row, so that we get a clear
+ * verification-related failure if there was an insertion
+ * race with another client. */
+ struct json *op = json_object_create();
+ json_array_add(operations, op);
+ json_object_put_string(op, "op", "wait");
+ json_object_put_string(op, "table", class->name);
+ json_object_put(op, "where", json_array_create_empty());
+ json_object_put(op, "timeout", json_integer_create(0));
+ json_object_put_string(op, "until", "==");
+ json_object_put(op, "rows", json_array_create_empty());
+ }
+
+ struct json *op = json_object_create();
+ json_object_put_string(op, "op",
+ row->old_datum ? "update" : "insert");
json_object_put_string(op, "table", class->name);
if (row->old_datum) {
json_object_put(op, "where", where_uuid_equals(&row->uuid));
diff --git a/ovsdb/ovsdb-idlc.in b/ovsdb/ovsdb-idlc.in
index c3973e4f5982..d07d527877a6 100755
--- a/ovsdb/ovsdb-idlc.in
+++ b/ovsdb/ovsdb-idlc.in
@@ -1298,9 +1298,13 @@ void
is_root = "true"
else:
is_root = "false"
- print(" {\"%s\", %s," % (tableName, is_root))
+ if table.max_rows == 1:
+ is_singleton = "true"
+ else:
+ is_singleton = "false"
+ print(" {\"%s\", %s, %s," % (tableName, is_root, is_singleton))
print(" %s_columns, ARRAY_SIZE(%s_columns)," % (
- structName, structName))
+ structName, structName))
print(" sizeof(struct %s), %s_init__}," % (structName, structName))
print("};")
--
2.10.2
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