Always refuse receving non-resume stream when resume state exists

This fixes a hole in the situation where the resume state is left from
receiving a new dataset and, so, the state is set on the dataset itself
(as opposed to %recv child).

Additionally, distinguish incremental and resume streams in error
messages.

Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andriy Gapon <avg@FreeBSD.org>
Closes #9252

lib/libzfs/libzfs_sendrecv.c

@@ -3992,11 +3992,18 @@ zfs_receive_one(libzfs_handle_t *hdl, int infd, const char *tosnap,
 		}
 	} else {
 		/*
-		 * if the fs does not exist, look for it based on the
-		 * fromsnap GUID
+		 * If the fs does not exist, look for it based on the
+		 * fromsnap GUID.
 		 */
-		(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
-		    "cannot receive incremental stream"));
+		if (resuming) {
+			(void) snprintf(errbuf, sizeof (errbuf),
+			    dgettext(TEXT_DOMAIN,
+			    "cannot receive resume stream"));
+		} else {
+			(void) snprintf(errbuf, sizeof (errbuf),
+			    dgettext(TEXT_DOMAIN,
+			    "cannot receive incremental stream"));
+		}
 
 		(void) strcpy(name, destsnap);
 		*strchr(name, '@') = '\0';

module/zfs/dmu_recv.c

@@ -86,21 +86,25 @@ recv_begin_check_existing_impl(dmu_recv_begin_arg_t *drba, dsl_dataset_t *ds,
 	boolean_t raw = (featureflags & DMU_BACKUP_FEATURE_RAW) != 0;
 	boolean_t embed = (featureflags & DMU_BACKUP_FEATURE_EMBED_DATA) != 0;
 
-	/* temporary clone name must not exist */
+	/* Temporary clone name must not exist. */
 	error = zap_lookup(dp->dp_meta_objset,
 	    dsl_dir_phys(ds->ds_dir)->dd_child_dir_zapobj, recv_clone_name,
 	    8, 1, &val);
 	if (error != ENOENT)
 		return (error == 0 ? EBUSY : error);
 
-	/* new snapshot name must not exist */
+	/* Resume state must not be set. */
+	if (dsl_dataset_has_resume_receive_state(ds))
+		return (SET_ERROR(EBUSY));
+
+	/* New snapshot name must not exist. */
 	error = zap_lookup(dp->dp_meta_objset,
 	    dsl_dataset_phys(ds)->ds_snapnames_zapobj,
 	    drba->drba_cookie->drc_tosnap, 8, 1, &val);
 	if (error != ENOENT)
 		return (error == 0 ? EEXIST : error);
 
-	/* must not have children if receiving a ZVOL */
+	/* Must not have children if receiving a ZVOL. */
 	error = zap_count(dp->dp_meta_objset,
 	    dsl_dir_phys(ds->ds_dir)->dd_child_dir_zapobj, &children);
 	if (error != 0)