tdb2: shrink free header from 32 to 24 bytes.

This reduces our minimum key+data length to 8 bytes; we do this by packing
the prev pointer where we used to put the flist pointer, and storing the
flist as an 8 bit index (meaning we can only have 256 free tables).

Note that this has a perverse result on the size of the database, as our
4-byte key and 4-byte data now fit perfectly in a minimal record, so
appeding causes us to allocate new records which are 50% larger,
since we detect growing.

Current results of speed test:
$ ./speed 1000000
Adding 1000000 records:  23210 ns (59193360 bytes)
Finding 1000000 records:  2387 ns (59193360 bytes)
Traversing 1000000 records:  2150 ns (59193360 bytes)
Deleting 1000000 records:  13392 ns (59193360 bytes)
Re-adding 1000000 records:  11546 ns (59193360 bytes)
Appending 1000000 records:  29327 ns (91193360 bytes)
Churning 1000000 records:  33026 ns (91193360 bytes)

Previous:
$ ./speed 1000000
Adding 1000000 records:  28324 ns (67232528 bytes)
Finding 1000000 records:  2468 ns (67232528 bytes)
Traversing 1000000 records:  2200 ns (67232528 bytes)
Deleting 1000000 records:  13083 ns (67232528 bytes)
Re-adding 1000000 records:  16433 ns (67232528 bytes)
Appending 1000000 records:  2511 ns (67232528 bytes)
Churning 1000000 records:  31068 ns (67570448 bytes)

ccan/tdb2/check.c

@@ -315,37 +315,37 @@ static bool check_hash(struct tdb_context *tdb,
 static bool check_free(struct tdb_context *tdb,
 		       tdb_off_t off,
 		       const struct tdb_free_record *frec,
-		       tdb_off_t prev, tdb_off_t flist_off, unsigned int bucket)
+		       tdb_off_t prev, unsigned int flist, unsigned int bucket)
 {
 	if (frec_magic(frec) != TDB_FREE_MAGIC) {
 		tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 			 "tdb_check: offset %llu bad magic 0x%llx\n",
-			 (long long)off, (long long)frec->magic_and_meta);
+			 (long long)off, (long long)frec->magic_and_prev);
 		return false;
 	}
-	if (frec_flist(frec) != flist_off) {
+	if (frec_flist(frec) != flist) {
 		tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
-			 "tdb_check: offset %llu bad freelist 0x%llx\n",
-			 (long long)off, (long long)frec_flist(frec));
+			 "tdb_check: offset %llu bad freelist %u\n",
+			 (long long)off, frec_flist(frec));
 		return false;
 	}
 
 	if (tdb->methods->oob(tdb, off
-			      + frec->data_len+sizeof(struct tdb_used_record),
+			      + frec_len(frec) + sizeof(struct tdb_used_record),
 			      false))
 		return false;
-	if (size_to_bucket(frec->data_len) != bucket) {
+	if (size_to_bucket(frec_len(frec)) != bucket) {
 		tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 			 "tdb_check: offset %llu in wrong bucket %u vs %u\n",
 			 (long long)off,
-			 bucket, size_to_bucket(frec->data_len));
+			 bucket, size_to_bucket(frec_len(frec)));
 		return false;
 	}
-	if (prev != frec->prev) {
+	if (prev != frec_prev(frec)) {
 		tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 			 "tdb_check: offset %llu bad prev %llu vs %llu\n",
 			 (long long)off,
-			 (long long)prev, (long long)frec->prev);
+			 (long long)prev, (long long)frec_len(frec));
 		return false;
 	}
 	return true;
@@ -353,6 +353,7 @@ static bool check_free(struct tdb_context *tdb,
 		       
 static bool check_free_list(struct tdb_context *tdb,
 			    tdb_off_t flist_off,
+			    unsigned flist_num,
 			    tdb_off_t free[],
 			    size_t num_free,
 			    size_t *num_found)
@@ -384,7 +385,7 @@ static bool check_free_list(struct tdb_context *tdb,
 				return false;
 			if (tdb_read_convert(tdb, off, &f, sizeof(f)))
 				return false;
-			if (!check_free(tdb, off, &f, prev, flist_off, i))
+			if (!check_free(tdb, off, &f, prev, flist_num, i))
 				return false;
 
 			/* FIXME: Check hash bits */
@@ -436,13 +437,17 @@ static bool check_linear(struct tdb_context *tdb,
 			struct tdb_free_record f;
 			struct tdb_recovery_record r;
 		} pad, *p;
-		p = tdb_get(tdb, off, &pad, sizeof(pad));
+		/* r is larger: only get that if we need to. */
+		p = tdb_get(tdb, off, &pad, sizeof(pad.f));
 		if (!p)
 			return false;
 
 		/* If we crash after ftruncate, we can get zeroes or fill. */
 		if (p->r.magic == TDB_RECOVERY_INVALID_MAGIC
 		    || p->r.magic ==  0x4343434343434343ULL) {
+			p = tdb_get(tdb, off, &pad, sizeof(pad.r));
+			if (!p)
+				return false;
 			if (recovery == off) {
 				found_recovery = true;
 				len = sizeof(p->r) + p->r.max_len;
@@ -462,6 +467,9 @@ static bool check_linear(struct tdb_context *tdb,
 					 (size_t)tdb->map_size);
 			}
 		} else if (p->r.magic == TDB_RECOVERY_MAGIC) {
+			p = tdb_get(tdb, off, &pad, sizeof(pad.r));
+			if (!p)
+				return false;
 			if (recovery != off) {
 				tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 					 "tdb_check: unexpected recovery"
@@ -469,11 +477,23 @@ static bool check_linear(struct tdb_context *tdb,
 					 (size_t)off);
 				return false;
 			}
+			if (p->r.len > p->r.max_len) {
+				tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
+					 "tdb_check: invalid recovery length"
+					 " %zu\n", (size_t)p->r.len);
+				return false;
+			}
+			if (p->r.eof > tdb->map_size) {
+				tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
+					 "tdb_check: invalid old EOF"
+					 " %zu\n", (size_t)p->r.eof);
+				return false;
+			}
 			found_recovery = true;
 			len = sizeof(p->r) + p->r.max_len;
 		} else if (frec_magic(&p->f) == TDB_FREE_MAGIC
 			   || frec_magic(&p->f) == TDB_COALESCING_MAGIC) {
-			len = sizeof(p->u) + p->f.data_len;
+			len = sizeof(p->u) + frec_len(&p->f);
 			if (off + len > tdb->map_size) {
 				tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 					 "tdb_check: free overlength %llu"
@@ -560,7 +580,8 @@ int tdb_check(struct tdb_context *tdb,
 	for (flist = first_flist(tdb); flist; flist = next_flist(tdb, flist)) {
 		if (flist == TDB_OFF_ERR)
 			goto fail;
-		if (!check_free_list(tdb, flist, free, num_free, &num_found))
+		if (!check_free_list(tdb, flist, num_flists, free, num_free,
+				     &num_found))
 			goto fail;
 		num_flists++;
 	}

ccan/tdb2/private.h

@@ -173,20 +173,30 @@ static inline uint16_t rec_magic(const struct tdb_used_record *r)
 }
 
 struct tdb_free_record {
-        uint64_t magic_and_meta; /* TDB_OFF_UPPER_STEAL bits of magic */
-        uint64_t data_len; /* Not counting these two fields. */
-	/* This is why the minimum record size is 16 bytes.  */
-	uint64_t next, prev;
+        uint64_t magic_and_prev; /* TDB_OFF_UPPER_STEAL bits magic, then prev */
+        uint64_t flist_and_len; /* Len not counting these two fields. */
+	/* This is why the minimum record size is 8 bytes.  */
+	uint64_t next;
 };
 
+static inline uint64_t frec_prev(const struct tdb_free_record *f)
+{
+	return f->magic_and_prev & ((1ULL << (64 - TDB_OFF_UPPER_STEAL)) - 1);
+}
+
 static inline uint64_t frec_magic(const struct tdb_free_record *f)
 {
-	return f->magic_and_meta >> (64 - TDB_OFF_UPPER_STEAL);
+	return f->magic_and_prev >> (64 - TDB_OFF_UPPER_STEAL);
+}
+
+static inline uint64_t frec_len(const struct tdb_free_record *f)
+{
+	return f->flist_and_len & ((1ULL << (64 - TDB_OFF_UPPER_STEAL))-1);
 }
 
-static inline uint64_t frec_flist(const struct tdb_free_record *f)
+static inline unsigned frec_flist(const struct tdb_free_record *f)
 {
-	return f->magic_and_meta & ((1ULL << (64 - TDB_OFF_UPPER_STEAL)) - 1);
+	return f->flist_and_len >> (64 - TDB_OFF_UPPER_STEAL);
 }
 
 struct tdb_recovery_record {
@@ -311,6 +321,7 @@ struct tdb_context {
 	
 	/* What freelist are we using? */
 	uint64_t flist_off;
+	unsigned int flist;
 
 	/* IO methods: changes for transactions. */
 	const struct tdb_methods *methods;

ccan/tdb2/summary.c

@@ -63,7 +63,7 @@ static bool summarize(struct tdb_context *tdb,
 		    || p->r.magic == TDB_RECOVERY_MAGIC) {
 			len = sizeof(p->r) + p->r.max_len;
 		} else if (rec_magic(&p->u) != TDB_MAGIC) {
-			len = p->f.data_len;
+			len = frec_len(&p->f);
 			tally_add(free, len);
 			tally_add(buckets, size_to_bucket(len));
 			len += sizeof(p->u);

ccan/tdb2/test/layout.c

@@ -136,9 +136,11 @@ static void set_freelist(void *mem, struct tdb_context *tdb,
 static void add_to_freetable(struct tdb_context *tdb,
 			     tdb_off_t eoff,
 			     tdb_off_t elen,
+			     unsigned flist,
 			     struct tle_freelist *freelist)
 {
 	tdb->flist_off = freelist->base.off;
+	tdb->flist = flist;
 	add_free_record(tdb, eoff, sizeof(struct tdb_used_record) + elen);
 }
 
@@ -288,6 +290,7 @@ struct tdb_context *tdb_layout_get(struct tdb_layout *layout)
 		switch (e->base.type) {
 		case FREE:
 			add_to_freetable(tdb, e->base.off, e->free.len,
+					 e->free.flist_num,
 					 find_flist(layout, e->free.flist_num));
 			break;
 		case DATA:

ccan/tdb2/test/run-03-coalesce.c

@@ -17,7 +17,7 @@ static tdb_len_t free_record_length(struct tdb_context *tdb, tdb_off_t off)
 		return TDB_OFF_ERR;
 	if (frec_magic(&f) != TDB_FREE_MAGIC)
 		return TDB_OFF_ERR;
-	return f.data_len;
+	return frec_len(&f);
 }
 
 int main(int argc, char *argv[])