Update vendor/illumos/dist and vendor-sys/illumos/dist

to illumos-gate 14052:1a272fe1337b

Illumos ZFS issues:
  3740 Poor ZFS send / receive performance due to snapshot
       hold / release processing

7 files changed, 161 insertions, 137 deletions

diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c
index 5e95aed..55368ff 100644
--- a/cmd/zfs/zfs_main.c
+++ b/cmd/zfs/zfs_main.c
@@ -25,6 +25,7 @@
  * Copyright (c) 2012 by Delphix. All rights reserved.
  * Copyright 2012 Milan Jurik. All rights reserved.
  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland.  All rights reserved.
  */
 
 #include <assert.h>
@@ -5164,8 +5165,7 @@ zfs_do_hold_rele_impl(int argc, char **argv, boolean_t holding)
 			continue;
 		}
 		if (holding) {
-			if (zfs_hold(zhp, delim+1, tag, recursive,
-			    B_FALSE, -1) != 0)
+			if (zfs_hold(zhp, delim+1, tag, recursive, -1) != 0)
 				++errors;
 		} else {
 			if (zfs_release(zhp, delim+1, tag, recursive) != 0)
diff --git a/cmd/zhack/zhack.c b/cmd/zhack/zhack.c
index d9ad36c..4e5e1e4 100644
--- a/cmd/zhack/zhack.c
+++ b/cmd/zhack/zhack.c
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 /*
@@ -153,7 +154,7 @@ import_pool(const char *target, boolean_t readonly)
 	g_importargs.poolname = g_pool;
 	pools = zpool_search_import(g_zfs, &g_importargs);
 
-	if (pools == NULL || nvlist_next_nvpair(pools, NULL) == NULL) {
+	if (nvlist_empty(pools)) {
 		if (!g_importargs.can_be_active) {
 			g_importargs.can_be_active = B_TRUE;
 			if (zpool_search_import(g_zfs, &g_importargs) != NULL ||
diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index 980615e..3aca1fe 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -22,6 +22,7 @@
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 /*
@@ -4711,7 +4712,7 @@ ztest_dmu_snapshot_hold(ztest_ds_t *zd, uint64_t id)
 
 	error = user_release_one(fullname, tag);
 	if (error)
-		fatal(0, "user_release_one(%s)", fullname, tag);
+		fatal(0, "user_release_one(%s, %s) = %d", fullname, tag, error);
 
 	VERIFY3U(dmu_objset_hold(fullname, FTAG, &origin), ==, ENOENT);
 
diff --git a/lib/libzfs/common/libzfs.h b/lib/libzfs/common/libzfs.h
index 4d1e818..cb84b62 100644
--- a/lib/libzfs/common/libzfs.h
+++ b/lib/libzfs/common/libzfs.h
@@ -24,6 +24,7 @@
  * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 #ifndef	_LIBZFS_H
@@ -594,7 +595,8 @@ extern int zfs_send(zfs_handle_t *, const char *, const char *,
 
 extern int zfs_promote(zfs_handle_t *);
 extern int zfs_hold(zfs_handle_t *, const char *, const char *,
-    boolean_t, boolean_t, int);
+    boolean_t, int);
+extern int zfs_hold_nvl(zfs_handle_t *, int, nvlist_t *);
 extern int zfs_release(zfs_handle_t *, const char *, const char *, boolean_t);
 extern int zfs_get_holds(zfs_handle_t *, nvlist_t **);
 extern uint64_t zvol_volsize_to_reservation(uint64_t, nvlist_t *);
diff --git a/lib/libzfs/common/libzfs_dataset.c b/lib/libzfs/common/libzfs_dataset.c
index 257b77e..635bc87 100644
--- a/lib/libzfs/common/libzfs_dataset.c
+++ b/lib/libzfs/common/libzfs_dataset.c
@@ -25,6 +25,7 @@
  * Copyright (c) 2012 DEY Storage Systems, Inc.  All rights reserved.
  * Copyright 2012 Nexenta Systems, Inc. All rights reserved.
  * Copyright (c) 2013 Martin Matuska. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 #include <ctype.h>
@@ -3104,18 +3105,14 @@ static int
 zfs_check_snap_cb(zfs_handle_t *zhp, void *arg)
 {
 	struct destroydata *dd = arg;
-	zfs_handle_t *szhp;
 	char name[ZFS_MAXNAMELEN];
 	int rv = 0;
 
 	(void) snprintf(name, sizeof (name),
 	    "%s@%s", zhp->zfs_name, dd->snapname);
 
-	szhp = make_dataset_handle(zhp->zfs_hdl, name);
-	if (szhp) {
+	if (lzc_exists(name))
 		verify(nvlist_add_boolean(dd->nvl, name) == 0);
-		zfs_close(szhp);
-	}
 
 	rv = zfs_iter_filesystems(zhp, zfs_check_snap_cb, dd);
 	zfs_close(zhp);
@@ -3135,7 +3132,7 @@ zfs_destroy_snaps(zfs_handle_t *zhp, char *snapname, boolean_t defer)
 	verify(nvlist_alloc(&dd.nvl, NV_UNIQUE_NAME, 0) == 0);
 	(void) zfs_check_snap_cb(zfs_handle_dup(zhp), &dd);
 
-	if (nvlist_next_nvpair(dd.nvl, NULL) == NULL) {
+	if (nvlist_empty(dd.nvl)) {
 		ret = zfs_standard_error_fmt(zhp->zfs_hdl, ENOENT,
 		    dgettext(TEXT_DOMAIN, "cannot destroy '%s@%s'"),
 		    zhp->zfs_name, snapname);
@@ -3160,7 +3157,7 @@ zfs_destroy_snaps_nvl(libzfs_handle_t *hdl, nvlist_t *snaps, boolean_t defer)
 	if (ret == 0)
 		return (0);
 
-	if (nvlist_next_nvpair(errlist, NULL) == NULL) {
+	if (nvlist_empty(errlist)) {
 		char errbuf[1024];
 		(void) snprintf(errbuf, sizeof (errbuf),
 		    dgettext(TEXT_DOMAIN, "cannot destroy snapshots"));
@@ -4082,18 +4079,14 @@ static int
 zfs_hold_one(zfs_handle_t *zhp, void *arg)
 {
 	struct holdarg *ha = arg;
-	zfs_handle_t *szhp;
 	char name[ZFS_MAXNAMELEN];
 	int rv = 0;
 
 	(void) snprintf(name, sizeof (name),
 	    "%s@%s", zhp->zfs_name, ha->snapname);
 
-	szhp = make_dataset_handle(zhp->zfs_hdl, name);
-	if (szhp) {
+	if (lzc_exists(name))
 		fnvlist_add_string(ha->nvl, name, ha->tag);
-		zfs_close(szhp);
-	}
 
 	if (ha->recursive)
 		rv = zfs_iter_filesystems(zhp, zfs_hold_one, ha);
@@ -4103,14 +4096,10 @@ zfs_hold_one(zfs_handle_t *zhp, void *arg)
 
 int
 zfs_hold(zfs_handle_t *zhp, const char *snapname, const char *tag,
-    boolean_t recursive, boolean_t enoent_ok, int cleanup_fd)
+    boolean_t recursive, int cleanup_fd)
 {
 	int ret;
 	struct holdarg ha;
-	nvlist_t *errors;
-	libzfs_handle_t *hdl = zhp->zfs_hdl;
-	char errbuf[1024];
-	nvpair_t *elem;
 
 	ha.nvl = fnvlist_alloc();
 	ha.snapname = snapname;
@@ -4118,26 +4107,44 @@ zfs_hold(zfs_handle_t *zhp, const char *snapname, const char *tag,
 	ha.recursive = recursive;
 	(void) zfs_hold_one(zfs_handle_dup(zhp), &ha);
 
-	if (nvlist_next_nvpair(ha.nvl, NULL) == NULL) {
+	if (nvlist_empty(ha.nvl)) {
+		char errbuf[1024];
+
 		fnvlist_free(ha.nvl);
 		ret = ENOENT;
-		if (!enoent_ok) {
-			(void) snprintf(errbuf, sizeof (errbuf),
-			    dgettext(TEXT_DOMAIN,
-			    "cannot hold snapshot '%s@%s'"),
-			    zhp->zfs_name, snapname);
-			(void) zfs_standard_error(hdl, ret, errbuf);
-		}
+		(void) snprintf(errbuf, sizeof (errbuf),
+		    dgettext(TEXT_DOMAIN,
+		    "cannot hold snapshot '%s@%s'"),
+		    zhp->zfs_name, snapname);
+		(void) zfs_standard_error(zhp->zfs_hdl, ret, errbuf);
 		return (ret);
 	}
 
-	ret = lzc_hold(ha.nvl, cleanup_fd, &errors);
+	ret = zfs_hold_nvl(zhp, cleanup_fd, ha.nvl);
 	fnvlist_free(ha.nvl);
 
-	if (ret == 0)
+	return (ret);
+}
+
+int
+zfs_hold_nvl(zfs_handle_t *zhp, int cleanup_fd, nvlist_t *holds)
+{
+	int ret;
+	nvlist_t *errors;
+	libzfs_handle_t *hdl = zhp->zfs_hdl;
+	char errbuf[1024];
+	nvpair_t *elem;
+
+	errors = NULL;
+	ret = lzc_hold(holds, cleanup_fd, &errors);
+
+	if (ret == 0) {
+		/* There may be errors even in the success case. */
+		fnvlist_free(errors);
 		return (0);
+	}
 
-	if (nvlist_next_nvpair(errors, NULL) == NULL) {
+	if (nvlist_empty(errors)) {
 		/* no hold-specific errors */
 		(void) snprintf(errbuf, sizeof (errbuf),
 		    dgettext(TEXT_DOMAIN, "cannot hold"));
@@ -4177,10 +4184,6 @@ zfs_hold(zfs_handle_t *zhp, const char *snapname, const char *tag,
 		case EEXIST:
 			(void) zfs_error(hdl, EZFS_REFTAG_HOLD, errbuf);
 			break;
-		case ENOENT:
-			if (enoent_ok)
-				return (ENOENT);
-			/* FALLTHROUGH */
 		default:
 			(void) zfs_standard_error(hdl,
 			    fnvpair_value_int32(elem), errbuf);
@@ -4191,30 +4194,21 @@ zfs_hold(zfs_handle_t *zhp, const char *snapname, const char *tag,
 	return (ret);
 }
 
-struct releasearg {
-	nvlist_t *nvl;
-	const char *snapname;
-	const char *tag;
-	boolean_t recursive;
-};
-
 static int
 zfs_release_one(zfs_handle_t *zhp, void *arg)
 {
 	struct holdarg *ha = arg;
-	zfs_handle_t *szhp;
 	char name[ZFS_MAXNAMELEN];
 	int rv = 0;
 
 	(void) snprintf(name, sizeof (name),
 	    "%s@%s", zhp->zfs_name, ha->snapname);
 
-	szhp = make_dataset_handle(zhp->zfs_hdl, name);
-	if (szhp) {
+	if (lzc_exists(name)) {
 		nvlist_t *holds = fnvlist_alloc();
 		fnvlist_add_boolean(holds, ha->tag);
 		fnvlist_add_nvlist(ha->nvl, name, holds);
-		zfs_close(szhp);
+		fnvlist_free(holds);
 	}
 
 	if (ha->recursive)
@@ -4229,7 +4223,7 @@ zfs_release(zfs_handle_t *zhp, const char *snapname, const char *tag,
 {
 	int ret;
 	struct holdarg ha;
-	nvlist_t *errors;
+	nvlist_t *errors = NULL;
 	nvpair_t *elem;
 	libzfs_handle_t *hdl = zhp->zfs_hdl;
 	char errbuf[1024];
@@ -4240,7 +4234,7 @@ zfs_release(zfs_handle_t *zhp, const char *snapname, const char *tag,
 	ha.recursive = recursive;
 	(void) zfs_release_one(zfs_handle_dup(zhp), &ha);
 
-	if (nvlist_next_nvpair(ha.nvl, NULL) == NULL) {
+	if (nvlist_empty(ha.nvl)) {
 		fnvlist_free(ha.nvl);
 		ret = ENOENT;
 		(void) snprintf(errbuf, sizeof (errbuf),
@@ -4254,10 +4248,13 @@ zfs_release(zfs_handle_t *zhp, const char *snapname, const char *tag,
 	ret = lzc_release(ha.nvl, &errors);
 	fnvlist_free(ha.nvl);
 
-	if (ret == 0)
+	if (ret == 0) {
+		/* There may be errors even in the success case. */
+		fnvlist_free(errors);
 		return (0);
+	}
 
-	if (nvlist_next_nvpair(errors, NULL) == NULL) {
+	if (nvlist_empty(errors)) {
 		/* no hold-specific errors */
 		(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
 		    "cannot release"));
diff --git a/lib/libzfs/common/libzfs_sendrecv.c b/lib/libzfs/common/libzfs_sendrecv.c
index ea0634e..cf6d32f 100644
--- a/lib/libzfs/common/libzfs_sendrecv.c
+++ b/lib/libzfs/common/libzfs_sendrecv.c
@@ -23,6 +23,7 @@
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012 by Delphix. All rights reserved.
  * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 #include <assert.h>
@@ -793,6 +794,7 @@ typedef struct send_dump_data {
 	int outfd;
 	boolean_t err;
 	nvlist_t *fss;
+	nvlist_t *snapholds;
 	avl_tree_t *fsavl;
 	snapfilter_cb_t *filter_cb;
 	void *filter_cb_arg;
@@ -942,41 +944,19 @@ dump_ioctl(zfs_handle_t *zhp, const char *fromsnap, uint64_t fromsnap_obj,
 	return (0);
 }
 
-static int
-hold_for_send(zfs_handle_t *zhp, send_dump_data_t *sdd)
+static void
+gather_holds(zfs_handle_t *zhp, send_dump_data_t *sdd)
 {
-	zfs_handle_t *pzhp;
-	int error = 0;
-	char *thissnap;
-
 	assert(zhp->zfs_type == ZFS_TYPE_SNAPSHOT);
 
-	if (sdd->dryrun)
-		return (0);
-
 	/*
-	 * zfs_send() only opens a cleanup_fd for sends that need it,
+	 * zfs_send() only sets snapholds for sends that need them,
 	 * e.g. replication and doall.
 	 */
-	if (sdd->cleanup_fd == -1)
-		return (0);
-
-	thissnap = strchr(zhp->zfs_name, '@') + 1;
-	*(thissnap - 1) = '\0';
-	pzhp = zfs_open(zhp->zfs_hdl, zhp->zfs_name, ZFS_TYPE_DATASET);
-	*(thissnap - 1) = '@';
-
-	/*
-	 * It's OK if the parent no longer exists.  The send code will
-	 * handle that error.
-	 */
-	if (pzhp) {
-		error = zfs_hold(pzhp, thissnap, sdd->holdtag,
-		    B_FALSE, B_TRUE, sdd->cleanup_fd);
-		zfs_close(pzhp);
-	}
+	if (sdd->snapholds == NULL)
+		return;
 
-	return (error);
+	fnvlist_add_string(sdd->snapholds, zhp->zfs_name, sdd->holdtag);
 }
 
 static void *
@@ -1032,28 +1012,23 @@ dump_snapshot(zfs_handle_t *zhp, void *arg)
 	send_dump_data_t *sdd = arg;
 	progress_arg_t pa = { 0 };
 	pthread_t tid;
-
 	char *thissnap;
 	int err;
 	boolean_t isfromsnap, istosnap, fromorigin;
 	boolean_t exclude = B_FALSE;
 
+	err = 0;
 	thissnap = strchr(zhp->zfs_name, '@') + 1;
 	isfromsnap = (sdd->fromsnap != NULL &&
 	    strcmp(sdd->fromsnap, thissnap) == 0);
 
 	if (!sdd->seenfrom && isfromsnap) {
-		err = hold_for_send(zhp, sdd);
-		if (err == 0) {
-			sdd->seenfrom = B_TRUE;
-			(void) strcpy(sdd->prevsnap, thissnap);
-			sdd->prevsnap_obj = zfs_prop_get_int(zhp,
-			    ZFS_PROP_OBJSETID);
-		} else if (err == ENOENT) {
-			err = 0;
-		}
+		gather_holds(zhp, sdd);
+		sdd->seenfrom = B_TRUE;
+		(void) strcpy(sdd->prevsnap, thissnap);
+		sdd->prevsnap_obj = zfs_prop_get_int(zhp, ZFS_PROP_OBJSETID);
 		zfs_close(zhp);
-		return (err);
+		return (0);
 	}
 
 	if (sdd->seento || !sdd->seenfrom) {
@@ -1104,14 +1079,7 @@ dump_snapshot(zfs_handle_t *zhp, void *arg)
 		return (0);
 	}
 
-	err = hold_for_send(zhp, sdd);
-	if (err) {
-		if (err == ENOENT)
-			err = 0;
-		zfs_close(zhp);
-		return (err);
-	}
-
+	gather_holds(zhp, sdd);
 	fromorigin = sdd->prevsnap[0] == '\0' &&
 	    (sdd->fromorigin || sdd->replicate);
 
@@ -1379,7 +1347,7 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 	avl_tree_t *fsavl = NULL;
 	static uint64_t holdseq;
 	int spa_version;
-	pthread_t tid;
+	pthread_t tid = 0;
 	int pipefd[2];
 	dedup_arg_t dda = { 0 };
 	int featureflags = 0;
@@ -1452,11 +1420,8 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 				*debugnvp = hdrnv;
 			else
 				nvlist_free(hdrnv);
-			if (err) {
-				fsavl_destroy(fsavl);
-				nvlist_free(fss);
+			if (err)
 				goto stderr_out;
-			}
 		}
 
 		if (!flags->dryrun) {
@@ -1480,8 +1445,6 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 			}
 			free(packbuf);
 			if (err == -1) {
-				fsavl_destroy(fsavl);
-				nvlist_free(fss);
 				err = errno;
 				goto stderr_out;
 			}
@@ -1492,8 +1455,6 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 			drr.drr_u.drr_end.drr_checksum = zc;
 			err = write(outfd, &drr, sizeof (drr));
 			if (err == -1) {
-				fsavl_destroy(fsavl);
-				nvlist_free(fss);
 				err = errno;
 				goto stderr_out;
 			}
@@ -1505,7 +1466,7 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 	/* dump each stream */
 	sdd.fromsnap = fromsnap;
 	sdd.tosnap = tosnap;
-	if (flags->dedup)
+	if (tid != 0)
 		sdd.outfd = pipefd[0];
 	else
 		sdd.outfd = outfd;
@@ -1542,36 +1503,71 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 			err = errno;
 			goto stderr_out;
 		}
+		sdd.snapholds = fnvlist_alloc();
 	} else {
 		sdd.cleanup_fd = -1;
+		sdd.snapholds = NULL;
 	}
-	if (flags->verbose) {
+	if (flags->verbose || sdd.snapholds != NULL) {
 		/*
 		 * Do a verbose no-op dry run to get all the verbose output
-		 * before generating any data.  Then do a non-verbose real
-		 * run to generate the streams.
+		 * or to gather snapshot hold's before generating any data,
+		 * then do a non-verbose real run to generate the streams.
 		 */
 		sdd.dryrun = B_TRUE;
 		err = dump_filesystems(zhp, &sdd);
-		sdd.dryrun = flags->dryrun;
-		sdd.verbose = B_FALSE;
-		if (flags->parsable) {
-			(void) fprintf(stderr, "size\t%llu\n",
-			    (longlong_t)sdd.size);
-		} else {
-			char buf[16];
-			zfs_nicenum(sdd.size, buf, sizeof (buf));
-			(void) fprintf(stderr, dgettext(TEXT_DOMAIN,
-			    "total estimated size is %s\n"), buf);
+
+		if (err != 0)
+			goto stderr_out;
+
+		if (flags->verbose) {
+			if (flags->parsable) {
+				(void) fprintf(stderr, "size\t%llu\n",
+				    (longlong_t)sdd.size);
+			} else {
+				char buf[16];
+				zfs_nicenum(sdd.size, buf, sizeof (buf));
+				(void) fprintf(stderr, dgettext(TEXT_DOMAIN,
+				    "total estimated size is %s\n"), buf);
+			}
+		}
+
+		/* Ensure no snaps found is treated as an error. */
+		if (!sdd.seento) {
+			err = ENOENT;
+			goto err_out;
 		}
+
+		/* Skip the second run if dryrun was requested. */
+		if (flags->dryrun)
+			goto err_out;
+
+		if (sdd.snapholds != NULL) {
+			err = zfs_hold_nvl(zhp, sdd.cleanup_fd, sdd.snapholds);
+			if (err != 0)
+				goto stderr_out;
+
+			fnvlist_free(sdd.snapholds);
+			sdd.snapholds = NULL;
+		}
+
+		sdd.dryrun = B_FALSE;
+		sdd.verbose = B_FALSE;
 	}
+
 	err = dump_filesystems(zhp, &sdd);
 	fsavl_destroy(fsavl);
 	nvlist_free(fss);
 
-	if (flags->dedup) {
-		(void) close(pipefd[0]);
+	/* Ensure no snaps found is treated as an error. */
+	if (err == 0 && !sdd.seento)
+		err = ENOENT;
+
+	if (tid != 0) {
+		if (err != 0)
+			(void) pthread_cancel(tid);
 		(void) pthread_join(tid, NULL);
+		(void) close(pipefd[0]);
 	}
 
 	if (sdd.cleanup_fd != -1) {
@@ -1599,9 +1595,13 @@ zfs_send(zfs_handle_t *zhp, const char *fromsnap, const char *tosnap,
 stderr_out:
 	err = zfs_standard_error(zhp->zfs_hdl, err, errbuf);
 err_out:
+	fsavl_destroy(fsavl);
+	nvlist_free(fss);
+	fnvlist_free(sdd.snapholds);
+
 	if (sdd.cleanup_fd != -1)
 		VERIFY(0 == close(sdd.cleanup_fd));
-	if (flags->dedup) {
+	if (tid != 0) {
 		(void) pthread_cancel(tid);
 		(void) pthread_join(tid, NULL);
 		(void) close(pipefd[0]);
diff --git a/lib/libzfs_core/common/libzfs_core.c b/lib/libzfs_core/common/libzfs_core.c
index 5e8ee07..990beaf 100644
--- a/lib/libzfs_core/common/libzfs_core.c
+++ b/lib/libzfs_core/common/libzfs_core.c
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 Steven Hartland. All rights reserved.
  */
 
 /*
@@ -254,8 +255,11 @@ lzc_snapshot(nvlist_t *snaps, nvlist_t *props, nvlist_t **errlist)
  * marked for deferred destruction, and will be destroyed when the last hold
  * or clone is removed/destroyed.
  *
+ * The return value will be ENOENT if none of the snapshots existed.
+ *
  * The return value will be 0 if all snapshots were destroyed (or marked for
- * later destruction if 'defer' is set) or didn't exist to begin with.
+ * later destruction if 'defer' is set) or didn't exist to begin with and
+ * at least one snapshot was destroyed.
  *
  * Otherwise the return value will be the errno of a (unspecified) snapshot
  * that failed, no snapshots will be destroyed, and the errlist will have an
@@ -286,7 +290,6 @@ lzc_destroy_snaps(nvlist_t *snaps, boolean_t defer, nvlist_t **errlist)
 	nvlist_free(args);
 
 	return (error);
-
 }
 
 int
@@ -346,11 +349,22 @@ lzc_exists(const char *dataset)
  * uncleanly, the holds will be released when the pool is next opened
  * or imported.
  *
- * The return value will be 0 if all holds were created. Otherwise the return
- * value will be the errno of a (unspecified) hold that failed, no holds will
- * be created, and the errlist will have an entry for each hold that
- * failed (name = snapshot).  The value in the errlist will be the error
- * code (int32).
+ * Holds for snapshots which don't exist will be skipped and have an entry
+ * added to errlist, but will not cause an overall failure, except in the
+ * case that all holds where skipped.
+ *
+ * The return value will be ENOENT if none of the snapshots for the requested
+ * holds existed.
+ *
+ * The return value will be 0 if the nvl holds was empty or all holds, for
+ * snapshots that existed, were succesfully created and at least one hold
+ * was created.
+ *
+ * Otherwise the return value will be the errno of a (unspecified) hold that
+ * failed and no holds will be created.
+ *
+ * In all cases the errlist will have an entry for each hold that failed
+ * (name = snapshot), with its value being the error code (int32).
  */
 int
 lzc_hold(nvlist_t *holds, int cleanup_fd, nvlist_t **errlist)
@@ -387,11 +401,20 @@ lzc_hold(nvlist_t *holds, int cleanup_fd, nvlist_t **errlist)
  * The snapshots must all be in the same pool.
  * The value is a nvlist whose keys are the holds to remove.
  *
- * The return value will be 0 if all holds were removed.
- * Otherwise the return value will be the errno of a (unspecified) release
- * that failed, no holds will be released, and the errlist will have an
- * entry for each snapshot that has failed releases (name = snapshot).
- * The value in the errlist will be the error code (int32) of a failed release.
+ * Holds which failed to release because they didn't exist will have an entry
+ * added to errlist, but will not cause an overall failure, except in the
+ * case that all releases where skipped.
+ *
+ * The return value will be ENOENT if none of the specified holds existed.
+ *
+ * The return value will be 0 if the nvl holds was empty or all holds that
+ * existed, were successfully removed and at least one hold was removed.
+ *
+ * Otherwise the return value will be the errno of a (unspecified) hold that
+ * failed to release and no holds will be released.
+ *
+ * In all cases the errlist will have an entry for each hold that failed to
+ * to release.
  */
 int
 lzc_release(nvlist_t *holds, nvlist_t **errlist)