lib/tdb_compat: header for tdb1 vs tdb2.

TDB2's API is slightly different from TDB1.  In particular, all functions
return 0 (TDB_SUCCESS) or a negative error number, rather than -1 or tdb_null
and storing the error in tdb_error() (though TDB2 does that as well).

The simplest fix is to replace all the different functions with a wrapper,
and that is done here.

Compatibility functions:

tdb_null: not used as an error return, so not defined by tdb2.
tdb_fetch_compat: TDB1-style data-returning tdb_fetch.
tdb_firstkey_compat: TDB1-style data-returning tdb_firstkey
tdb_nextkey_compat: TDB1-style data-returning tdb_nextkey, with
	TDB2-style free of old key.
tdb_errorstr_compat: TDB1-style tdb_errorstr() which takes TDB instead of ecode.
TDB_CONTEXT: TDB1-style typedef for struct tdb_context.
tdb_open_compat: Simplified open routine which takes log function, sets
	TDB_ALLOW_NESTING as Samba expects, and adds TDB_CLEAR_IF_FIRST support.

Things defined away in TDB2 wrappers:

tdb_traverse_read: TDB2's tdb_traverse only uses read-locks anyway.
tdb_reopen/tdb_reopen_all: TDB2 detects this error itself.
TDB_INCOMPATIBLE_HASH: TDB2 uses the Jenkins hash already.
TDB_VOLATILE: TDB2 shouldn't have freelist scaling issues.

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

1 files changed, 96 insertions, 0 deletions

diff --git a/lib/tdb_compat/tdb_compat.c b/lib/tdb_compat/tdb_compat.c
new file mode 100644
index 0000000000..f432296a40
--- /dev/null
+++ b/lib/tdb_compat/tdb_compat.c
@@ -0,0 +1,96 @@
+#include <tdb_compat.h>
+
+/* Note: for the moment, we only need this file for TDB2, so we can
+ * assume waf. */
+#if BUILD_TDB2
+TDB_DATA tdb_null = { NULL, 0 };
+
+/* Proxy which sets waitflag to false so we never block. */
+static int lock_nonblock(int fd, int rw, off_t off, off_t len, bool waitflag,
+			 void *_orig)
+{
+	struct tdb_attribute_flock *orig = _orig;
+
+	return orig->lock(fd, rw, off, len, false, orig->data);
+}
+
+enum TDB_ERROR tdb_transaction_start_nonblock(struct tdb_context *tdb)
+{
+	union tdb_attribute locking, orig;
+	enum TDB_ERROR ecode;
+
+	orig.base.attr = TDB_ATTRIBUTE_FLOCK;
+	ecode = tdb_get_attribute(tdb, &orig);
+	if (ecode != TDB_SUCCESS)
+		return ecode;
+
+	/* Replace locking function with our own. */
+	locking = orig;
+	locking.flock.data = &orig;
+	locking.flock.lock = lock_nonblock;
+
+	ecode = tdb_set_attribute(tdb, &locking);
+	if (ecode != TDB_SUCCESS)
+		return ecode;
+
+	ecode = tdb_transaction_start(tdb);
+	tdb_unset_attribute(tdb, TDB_ATTRIBUTE_FLOCK);
+	return ecode;
+}
+
+/*
+ * This handles TDB_CLEAR_IF_FIRST.
+ */
+static enum TDB_ERROR clear_if_first(int fd, void *unused)
+{
+	/* We hold a lock offset 63 always, so we can tell if anyone else is. */
+	struct flock fl;
+
+	fl.l_type = F_WRLCK;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = 63;
+	fl.l_len = 1;
+
+	if (fcntl(fd, F_SETLK, &fl) == 0) {
+		/* We must be first ones to open it w/ TDB_CLEAR_IF_FIRST! */
+		if (ftruncate(fd, 0) != 0) {
+			return TDB_ERR_IO;
+		}
+	}
+	fl.l_type = F_RDLCK;
+	if (fcntl(fd, F_SETLKW, &fl) != 0) {
+		return TDB_ERR_IO;
+	}
+	return TDB_SUCCESS;
+}
+
+struct tdb_context *
+tdb_open_compat_(const char *name, int hash_size_unused,
+		 int tdb_flags, int open_flags, mode_t mode,
+		 void (*log_fn)(struct tdb_context *,
+				enum tdb_log_level,
+				const char *message,
+				void *data),
+		 void *log_data)
+{
+	union tdb_attribute cif, log, *attr = NULL;
+
+	if (log_fn) {
+		log.log.base.attr = TDB_ATTRIBUTE_LOG;
+		log.log.base.next = NULL;
+		log.log.fn = log_fn;
+		log.log.data = log_data;
+		attr = &log;
+	}
+
+	if (tdb_flags & TDB_CLEAR_IF_FIRST) {
+		cif.openhook.base.attr = TDB_ATTRIBUTE_OPENHOOK;
+		cif.openhook.base.next = attr;
+		cif.openhook.fn = clear_if_first;
+		attr = &cif;
+		tdb_flags &= ~TDB_CLEAR_IF_FIRST;
+	}
+	return tdb_open(name, tdb_flags|TDB_ALLOW_NESTING, open_flags, mode,
+			attr);
+}
+#endif