zap: add zap_increment_by_dnode()

Make consistent with the standard pattern, with zap_increment() becoming
a simple wrapper around zap_increment_by_dnode().

This has a small, likely unnoticeable, behaviour change. The previous
version didn't use the _by_dnode() functions, so the ZAP, dnode and dbuf
could theoretically be evicted between calls. With the dnode held across
the calls, this won't happen anymore. This is almost certainly a good
thing.

Sponsored-by: TrueNAS
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@truenas.com>
Closes #18630

include/sys/zap.h

@@ -370,6 +370,8 @@ int zap_count_by_dnode(dnode_t *dn, uint64_t *count);
  */
 int zap_increment(objset_t *os, uint64_t obj, const char *name, int64_t delta,
     dmu_tx_t *tx);
+int zap_increment_by_dnode(dnode_t *dn, const char *name, int64_t delta,
+    dmu_tx_t *tx);
 
 /*
  * Returns (in name) the name of the entry whose (value & mask)

module/zfs/zap.c

@@ -872,7 +872,7 @@ zap_count(objset_t *os, uint64_t zapobj, uint64_t *count)
 /* zap_increment */
 
 int
-zap_increment(objset_t *os, uint64_t obj, const char *name, int64_t delta,
+zap_increment_by_dnode(dnode_t *dn, const char *name, int64_t delta,
     dmu_tx_t *tx)
 {
 	uint64_t value = 0;
@@ -880,14 +880,27 @@ zap_increment(objset_t *os, uint64_t obj, const char *name, int64_t delta,
 	if (delta == 0)
 		return (0);
 
-	int err = zap_lookup(os, obj, name, 8, 1, &value);
+	int err = zap_lookup_by_dnode(dn, name, 8, 1, &value);
 	if (err != 0 && err != ENOENT)
 		return (err);
 	value += delta;
 	if (value == 0)
-		err = zap_remove(os, obj, name, tx);
+		err = zap_remove_by_dnode(dn, name, tx);
 	else
-		err = zap_update(os, obj, name, 8, 1, &value, tx);
+		err = zap_update_by_dnode(dn, name, 8, 1, &value, tx);
+	return (err);
+}
+
+int
+zap_increment(objset_t *os, uint64_t zapobj, const char *name, int64_t delta,
+    dmu_tx_t *tx)
+{
+	dnode_t *dn;
+	int err = dnode_hold(os, zapobj, FTAG, &dn);
+	if (err != 0)
+		return (err);
+	err = zap_increment_by_dnode(dn, name, delta, tx);
+	dnode_rele(dn, FTAG);
 	return (err);
 }