Simplify resume token generation

* Improve naming.
* Reduce indentation.
* Avoid boilerplate logic duplication.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes #12967

include/sys/dsl_dataset.h

@@ -385,8 +385,7 @@ int dsl_dataset_snap_lookup(dsl_dataset_t *ds, const char *name,
 void dsl_dataset_dirty(dsl_dataset_t *ds, dmu_tx_t *tx);
 
 int get_clones_stat_impl(dsl_dataset_t *ds, nvlist_t *val);
-char *get_receive_resume_stats_impl(dsl_dataset_t *ds);
+char *get_receive_resume_token(dsl_dataset_t *ds);
-char *get_child_receive_stats(dsl_dataset_t *ds);
 uint64_t dsl_get_refratio(dsl_dataset_t *ds);
 uint64_t dsl_get_logicalreferenced(dsl_dataset_t *ds);
 uint64_t dsl_get_compressratio(dsl_dataset_t *ds);

module/zfs/dsl_dataset.c

@@ -2331,16 +2331,13 @@ get_clones_stat(dsl_dataset_t *ds, nvlist_t *nv)
 	nvlist_free(propval);
 }
 
-/*
+static char *
- * Returns a string that represents the receive resume stats token. It should
+get_receive_resume_token_impl(dsl_dataset_t *ds)
- * be freed with strfree().
- */
-char *
-get_receive_resume_stats_impl(dsl_dataset_t *ds)
 {
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	if (!dsl_dataset_has_resume_receive_state(ds))
+		return (NULL);
 
-	if (dsl_dataset_has_resume_receive_state(ds)) {
+	dsl_pool_t *dp = ds->ds_dir->dd_pool;
 	char *str;
 	void *packed;
 	uint8_t *compressed;
@@ -2444,48 +2441,37 @@ get_receive_resume_stats_impl(dsl_dataset_t *ds)
 	kmem_free(compressed, packed_size);
 	return (propval);
 }
-	return (kmem_strdup(""));
-}
 
 /*
- * Returns a string that represents the receive resume stats token of the
+ * Returns a string that represents the receive resume state token. It should
- * dataset's child. It should be freed with strfree().
+ * be freed with strfree(). NULL is returned if no resume state is present.
  */
 char *
-get_child_receive_stats(dsl_dataset_t *ds)
+get_receive_resume_token(dsl_dataset_t *ds)
 {
-	char recvname[ZFS_MAX_DATASET_NAME_LEN + 6];
+	/*
+	 * A failed "newfs" (e.g. full) resumable receive leaves
+	 * the stats set on this dataset.  Check here for the prop.
+	 */
+	char *token = get_receive_resume_token_impl(ds);
+	if (token != NULL)
+		return (token);
+	/*
+	 * A failed incremental resumable receive leaves the
+	 * stats set on our child named "%recv".  Check the child
+	 * for the prop.
+	 */
+	/* 6 extra bytes for /%recv */
+	char name[ZFS_MAX_DATASET_NAME_LEN + 6];
 	dsl_dataset_t *recv_ds;
-	dsl_dataset_name(ds, recvname);
+	dsl_dataset_name(ds, name);
-	if (strlcat(recvname, "/", sizeof (recvname)) <
+	if (strlcat(name, "/", sizeof (name)) < sizeof (name) &&
-	    sizeof (recvname) &&
+	    strlcat(name, recv_clone_name, sizeof (name)) < sizeof (name) &&
-	    strlcat(recvname, recv_clone_name, sizeof (recvname)) <
+	    dsl_dataset_hold(ds->ds_dir->dd_pool, name, FTAG, &recv_ds) == 0) {
-	    sizeof (recvname) &&
+		token = get_receive_resume_token_impl(recv_ds);
-	    dsl_dataset_hold(ds->ds_dir->dd_pool, recvname, FTAG,
-	    &recv_ds)  == 0) {
-		char *propval = get_receive_resume_stats_impl(recv_ds);
 		dsl_dataset_rele(recv_ds, FTAG);
-		return (propval);
 	}
-	return (kmem_strdup(""));
+	return (token);
-}
-
-static void
-get_receive_resume_stats(dsl_dataset_t *ds, nvlist_t *nv)
-{
-	char *propval = get_receive_resume_stats_impl(ds);
-	if (strcmp(propval, "") != 0) {
-		dsl_prop_nvlist_add_string(nv,
-		    ZFS_PROP_RECEIVE_RESUME_TOKEN, propval);
-	} else {
-		char *childval = get_child_receive_stats(ds);
-		if (strcmp(childval, "") != 0) {
-			dsl_prop_nvlist_add_string(nv,
-			    ZFS_PROP_RECEIVE_RESUME_TOKEN, childval);
-		}
-		kmem_strfree(childval);
-	}
-	kmem_strfree(propval);
 }
 
 uint64_t
@@ -2761,7 +2747,7 @@ dsl_get_mountpoint(dsl_dataset_t *ds, const char *dsname, char *value,
 void
 dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 {
-	dsl_pool_t *dp = ds->ds_dir->dd_pool;
+	dsl_pool_t *dp __maybe_unused = ds->ds_dir->dd_pool;
 
 	ASSERT(dsl_pool_config_held(dp));
 
@@ -2823,28 +2809,11 @@ dsl_dataset_stats(dsl_dataset_t *ds, nvlist_t *nv)
 	}
 
 	if (!dsl_dataset_is_snapshot(ds)) {
-		/*
+		char *token = get_receive_resume_token(ds);
-		 * A failed "newfs" (e.g. full) resumable receive leaves
+		if (token != NULL) {
-		 * the stats set on this dataset.  Check here for the prop.
+			dsl_prop_nvlist_add_string(nv,
-		 */
+			    ZFS_PROP_RECEIVE_RESUME_TOKEN, token);
-		get_receive_resume_stats(ds, nv);
+			kmem_strfree(token);
-
-		/*
-		 * A failed incremental resumable receive leaves the
-		 * stats set on our child named "%recv".  Check the child
-		 * for the prop.
-		 */
-		/* 6 extra bytes for /%recv */
-		char recvname[ZFS_MAX_DATASET_NAME_LEN + 6];
-		dsl_dataset_t *recv_ds;
-		dsl_dataset_name(ds, recvname);
-		if (strlcat(recvname, "/", sizeof (recvname)) <
-		    sizeof (recvname) &&
-		    strlcat(recvname, recv_clone_name, sizeof (recvname)) <
-		    sizeof (recvname) &&
-		    dsl_dataset_hold(dp, recvname, FTAG, &recv_ds) == 0) {
-			get_receive_resume_stats(recv_ds, nv);
-			dsl_dataset_rele(recv_ds, FTAG);
 		}
 	}
 }

module/zfs/zcp_get.c

@@ -344,19 +344,13 @@ get_special_prop(lua_State *state, dsl_dataset_t *ds, const char *dsname,
 		}
 		break;
 	case ZFS_PROP_RECEIVE_RESUME_TOKEN: {
-		char *token = get_receive_resume_stats_impl(ds);
+		char *token = get_receive_resume_token(ds);
-
+		if (token != NULL) {
 			(void) strlcpy(strval, token, ZAP_MAXVALUELEN);
-		if (strcmp(strval, "") == 0) {
-			char *childval = get_child_receive_stats(ds);
-
-			(void) strlcpy(strval, childval, ZAP_MAXVALUELEN);
-			if (strcmp(strval, "") == 0)
-				error = ENOENT;
-
-			kmem_strfree(childval);
-		}
 			kmem_strfree(token);
+		} else {
+			error = ENOENT;
+		}
 		break;
 	}
 	case ZFS_PROP_VOLSIZE: