zap: add zap_value_search_by_dnode()

This operates entirely on a cursor, so the two entry points just
instantiate a new cursor and then pass it into the worker.

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

@@ -381,6 +381,8 @@ int zap_increment_by_dnode(dnode_t *dn, const char *name, int64_t delta,
  */
 int zap_value_search(objset_t *os, uint64_t zapobj,
     uint64_t value, uint64_t mask, char *name, uint64_t namelen);
+int zap_value_search_by_dnode(dnode_t *dn,
+    uint64_t value, uint64_t mask, char *name, uint64_t namelen);
 
 /*
  * Manipulate entries where the name + value are the "same" (the name is

module/zfs/zap.c

@@ -906,31 +906,47 @@ zap_increment(objset_t *os, uint64_t zapobj, const char *name, int64_t delta,
 
 /* zap_value_search */
 
-int
-zap_value_search(objset_t *os, uint64_t zapobj, uint64_t value, uint64_t mask,
+static int
+zap_value_search_impl(zap_cursor_t *zc, uint64_t value, uint64_t mask,
     char *name, uint64_t namelen)
 {
-	zap_cursor_t zc;
 	int err;
 
 	if (mask == 0)
 		mask = -1ULL;
 
 	zap_attribute_t *za = zap_attribute_long_alloc();
-	for (zap_cursor_init(&zc, os, zapobj);
-	    (err = zap_cursor_retrieve(&zc, za)) == 0;
-	    zap_cursor_advance(&zc)) {
+	for (; (err = zap_cursor_retrieve(zc, za)) == 0;
+	    zap_cursor_advance(zc)) {
 		if ((za->za_first_integer & mask) == (value & mask)) {
 			if (strlcpy(name, za->za_name, namelen) >= namelen)
 				err = SET_ERROR(ENAMETOOLONG);
 			break;
 		}
 	}
-	zap_cursor_fini(&zc);
+	zap_cursor_fini(zc);
 	zap_attribute_free(za);
 	return (err);
 }
 
+int
+zap_value_search(objset_t *os, uint64_t zapobj, uint64_t value, uint64_t mask,
+    char *name, uint64_t namelen)
+{
+	zap_cursor_t zc;
+	zap_cursor_init(&zc, os, zapobj);
+	return (zap_value_search_impl(&zc, value, mask, name, namelen));
+}
+
+int
+zap_value_search_by_dnode(dnode_t *dn, uint64_t value, uint64_t mask,
+    char *name, uint64_t namelen)
+{
+	zap_cursor_t zc;
+	zap_cursor_init_by_dnode(&zc, dn);
+	return (zap_value_search_impl(&zc, value, mask, name, namelen));
+}
+
 /* zap_*_int */
 
 #define	FORMAT_INT_KEY(name, value)	\