tdb_compat: make tdb2s temporarily read-only for tdb_traverse_read()

It doesn't make a difference unless the tdb2 opens a TDB1 on disk, in
which case tdb1_traverse() takes a write lock on the entire file.  By
setting the tdb to read-only first, we simulate the old behaviour.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 27 insertions, 2 deletions

diff --git a/lib/tdb_compat/tdb_compat.c b/lib/tdb_compat/tdb_compat.c
index d736db1742..2e43564802 100644
--- a/lib/tdb_compat/tdb_compat.c
+++ b/lib/tdb_compat/tdb_compat.c
@@ -38,6 +38,26 @@ enum TDB_ERROR tdb_transaction_start_nonblock(struct tdb_context *tdb)
 	return ecode;
 }
 
+/* For TDB1 tdbs, read traverse vs normal matters: write traverse
+   locks the entire thing! */
+int64_t tdb_traverse_read_(struct tdb_context *tdb,
+			   int (*fn)(struct tdb_context *,
+						       TDB_DATA, TDB_DATA,
+						       void *),
+			   void *p)
+{
+	int64_t ret;
+
+	if (tdb_get_flags(tdb) & TDB_RDONLY) {
+		return tdb_traverse(tdb, fn, p);
+	}
+
+	tdb_add_flag(tdb, TDB_RDONLY);
+	ret = tdb_traverse(tdb, fn, p);
+	tdb_remove_flag(tdb, TDB_RDONLY);
+	return ret;
+}
+
 /*
  * This handles TDB_CLEAR_IF_FIRST.
  */
diff --git a/lib/tdb_compat/tdb_compat.h b/lib/tdb_compat/tdb_compat.h
index 80fc3cef80..16d1f48c7d 100644
--- a/lib/tdb_compat/tdb_compat.h
+++ b/lib/tdb_compat/tdb_compat.h
@@ -62,8 +62,13 @@ static inline TDB_DATA tdb_nextkey_compat(struct tdb_context *tdb, TDB_DATA k)
 	return k;
 }
 
-/* tdb_traverse_read and tdb_traverse are equal: both only take read locks. */
-#define tdb_traverse_read tdb_traverse
+#define tdb_traverse_read(tdb, fn, p)					\
+	tdb_traverse_read_(tdb, typesafe_cb_preargs(int, void *, (fn), (p), \
+						    struct tdb_context *, \
+						    TDB_DATA, TDB_DATA), (p))
+int64_t tdb_traverse_read_(struct tdb_context *tdb,
+			   int (*fn)(struct tdb_context *,
+				     TDB_DATA, TDB_DATA, void *), void *p);
 
 /* Old-style tdb_errorstr */
 #define tdb_errorstr_compat(tdb) tdb_errorstr(tdb_error(tdb))