tdb2: feature support.

As detailed in doc/design.lyx section 2.15 "Extending The Header Is
Difficult"; we add features_used and features_offered fields to the
header, so we can identify if we add new features, and then if someone
opens it who doesn't understand that feature.

ccan/tdb2/doc/design.lyx

@@ -1398,7 +1398,13 @@ Status
 \end_layout
 
 \begin_layout Standard
+
+\change_deleted 0 1300360753
 Incomplete.
+\change_inserted 0 1300360754
+Complete.
+\change_unchanged
+
 \end_layout
 
 \begin_layout Subsection

ccan/tdb2/private.h

@@ -116,6 +116,9 @@ typedef int tdb_bool_err;
 #define TDB_OFF_HASH_EXTRA_BIT 57
 #define TDB_OFF_UPPER_STEAL_SUBHASH_BIT 56
 
+/* Additional features we understand.  Currently: none. */
+#define TDB_FEATURE_MASK ((uint64_t)0)
+
 /* The bit number where we store the extra hash bits. */
 /* Convenience mask to get actual offset. */
 #define TDB_OFF_MASK \
@@ -240,7 +243,10 @@ struct tdb_header {
 	tdb_off_t free_table; /* (First) free table. */
 	tdb_off_t recovery; /* Transaction recovery area. */
 
-	tdb_off_t reserved[26];
+	uint64_t features_used; /* Features all writers understand */
+	uint64_t features_offered; /* Features offered */
+
+	tdb_off_t reserved[24];
 
 	/* Top level hash table. */
 	tdb_off_t hashtable[1ULL << TDB_TOPLEVEL_HASH_BITS];

ccan/tdb2/tdb.c

@@ -112,6 +112,7 @@ static enum TDB_ERROR tdb_new_database(struct tdb_context *tdb,
 					 newdb.hdr.hash_seed,
 					 tdb->hash_priv);
 	newdb.hdr.recovery = 0;
+	newdb.hdr.features_used = newdb.hdr.features_offered = TDB_FEATURE_MASK;
 	memset(newdb.hdr.reserved, 0, sizeof(newdb.hdr.reserved));
 	/* Initial hashes are empty. */
 	memset(newdb.hdr.hashtable, 0, sizeof(newdb.hdr.hashtable));
@@ -361,6 +362,16 @@ struct tdb_context *tdb_open(const char *name, int tdb_flags,
 		goto fail;
 	}
 
+	/* Clear any features we don't understand. */
+ 	if ((open_flags & O_ACCMODE) != O_RDONLY) {
+		hdr.features_used &= TDB_FEATURE_MASK;
+		if (tdb_write_convert(tdb, offsetof(struct tdb_header,
+						    features_used),
+				      &hdr.features_used,
+				      sizeof(hdr.features_used)) == -1)
+			goto fail;
+	}
+
 	tdb->device = st.st_dev;
 	tdb->inode = st.st_ino;
 	tdb_unlock_open(tdb);

ccan/tdb2/test/failtest_helper.h

@@ -4,7 +4,7 @@
 #include <stdbool.h>
 
 /* FIXME: Check these! */
-#define INITIAL_TDB_MALLOC	"tdb.c", 190, FAILTEST_MALLOC
+#define INITIAL_TDB_MALLOC	"tdb.c", 191, FAILTEST_MALLOC
 #define URANDOM_OPEN		"tdb.c", 49, FAILTEST_OPEN
 #define URANDOM_READ		"tdb.c", 29, FAILTEST_READ
 

ccan/tdb2/test/run-features.c

@@ -0,0 +1,71 @@
+#include <ccan/tdb2/tdb.c>
+#include <ccan/tdb2/free.c>
+#include <ccan/tdb2/lock.c>
+#include <ccan/tdb2/io.c>
+#include <ccan/tdb2/hash.c>
+#include <ccan/tdb2/check.c>
+#include <ccan/tdb2/summary.c>
+#include <ccan/tdb2/transaction.c>
+#include <ccan/tap/tap.h>
+#include "logging.h"
+
+int main(int argc, char *argv[])
+{
+	unsigned int i, j;
+	struct tdb_context *tdb;
+	int flags[] = { TDB_DEFAULT, TDB_NOMMAP,
+			TDB_CONVERT, TDB_NOMMAP|TDB_CONVERT };
+	struct tdb_data key = { (unsigned char *)&j, sizeof(j) };
+	struct tdb_data data = { (unsigned char *)&j, sizeof(j) };
+
+	plan_tests(sizeof(flags) / sizeof(flags[0]) * 8 + 1);
+	for (i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
+		uint64_t features;
+		tdb = tdb_open("run-features.tdb", flags[i],
+			       O_RDWR|O_CREAT|O_TRUNC, 0600, &tap_log_attr);
+		ok1(tdb);
+		if (!tdb)
+			continue;
+
+		/* Put some stuff in there. */
+		for (j = 0; j < 100; j++) {
+			if (tdb_store(tdb, key, data, TDB_REPLACE) != 0)
+				fail("Storing in tdb");
+		}
+
+		/* Mess with features fields in hdr. */
+		features = (~TDB_FEATURE_MASK ^ 1);
+		ok1(tdb_write_convert(tdb, offsetof(struct tdb_header,
+						    features_used), 
+				      &features, sizeof(features)) == 0);
+		ok1(tdb_write_convert(tdb, offsetof(struct tdb_header,
+						    features_offered), 
+				      &features, sizeof(features)) == 0);
+		tdb_close(tdb);
+
+		tdb = tdb_open("run-features.tdb", flags[i], O_RDWR, 0,
+			       &tap_log_attr);
+		ok1(tdb);
+		if (!tdb)
+			continue;
+
+		/* Should not have changed features offered. */
+		ok1(tdb_read_convert(tdb, offsetof(struct tdb_header,
+						   features_offered), 
+				     &features, sizeof(features)) == 0);
+		ok1(features == (~TDB_FEATURE_MASK ^ 1));
+
+		/* Should have cleared unknown bits in features_used. */
+		ok1(tdb_read_convert(tdb, offsetof(struct tdb_header,
+						   features_used), 
+				     &features, sizeof(features)) == 0);
+		ok1(features == (1 & TDB_FEATURE_MASK));
+
+		tdb_close(tdb);
+	}
+
+	ok1(tap_log_messages == 0);
+	return exit_status();
+}
+
+