deprecate deduplicated send streams

cmd/zfs/zfs_main.c

@@ -4328,6 +4328,16 @@ zfs_do_send(int argc, char **argv)
 		}
 	}
 
+	if (flags.dedup) {
+		(void) fprintf(stderr,
+		    gettext("WARNING: deduplicated send is "
+		    "deprecated, and will be removed in a\n"
+		    "future release. (In the future, the flag will be "
+		    "accepted, but a\n"
+		    "regular, non-deduplicated stream will be "
+		    "generated.)\n\n"));
+	}
+
 	if (flags.parsable && flags.verbosity == 0)
 		flags.verbosity = 1;
 

include/libzfs_impl.h

@@ -71,6 +71,7 @@ struct libzfs_handle {
 	int libzfs_pool_iter;
 	char libzfs_chassis_id[256];
 	boolean_t libzfs_prop_debug;
+	boolean_t libzfs_dedup_warning_printed;
 };
 
 #define	ZFSSHARE_MISS	0x01	/* Didn't find entry in cache */

lib/libzfs/libzfs_sendrecv.c

@@ -4699,6 +4699,26 @@ zfs_receive_one(libzfs_handle_t *hdl, int infd, const char *tosnap,
 			(void) printf("found clone origin %s\n", origin);
 	}
 
+	if (!hdl->libzfs_dedup_warning_printed &&
+	    (DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo) &
+	    DMU_BACKUP_FEATURE_DEDUP)) {
+		(void) fprintf(stderr,
+		    gettext("WARNING: This is a deduplicated send stream.  "
+		    "The ability to send and\n"
+		    "receive deduplicated send streams is deprecated.  "
+		    "In the future, the\n"
+		    "ability to receive a deduplicated send stream with "
+		    "\"zfs receive\" will be\n"
+		    "removed. However, in the future, a utility will be "
+		    "provided to convert a\n"
+		    "deduplicated send stream to a regular "
+		    "(non-deduplicated) stream. This\n"
+		    "future utility will require that the send stream be "
+		    "located in a\n"
+		    "seek-able file, rather than provided by a pipe.\n\n"));
+		hdl->libzfs_dedup_warning_printed = B_TRUE;
+	}
+
 	boolean_t resuming = DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo) &
 	    DMU_BACKUP_FEATURE_RESUMING;
 	boolean_t raw = DMU_GET_FEATUREFLAGS(drrb->drr_versioninfo) &

man/man8/zfs-receive.8

@@ -105,6 +105,18 @@ destroyed by using the
 .Nm zfs Cm destroy Fl d
 command.
 .Pp
+Deduplicated send streams can be generated by using the
+.Nm zfs Cm send Fl D
+command.
+\fBThe ability to send and receive deduplicated send streams is deprecated.\fR
+In the future, the ability to receive a deduplicated send stream with
+.Nm zfs Cm receive
+will be removed.
+However, in the future, a utility will be provided to convert a
+deduplicated send stream to a regular (non-deduplicated) stream.
+This future utility will require that the send stream be located in a
+seek-able file, rather than provided by a pipe.
+.Pp
 If
 .Fl o Em property Ns = Ns Ar value
 or

man/man8/zfs-send.8

@@ -87,6 +87,9 @@ By default, a full stream is generated.
 .Bl -tag -width "-D"
 .It Fl D, -dedup
 Generate a deduplicated stream.
+\fBDeduplicated send is deprecated and will be removed in a future release.\fR
+(In the future, the flag will be accepted but a regular, non-deduplicated
+stream will be generated.)
 Blocks which would have been sent multiple times in the send stream will only be
 sent once.
 The receiving system must also support this feature to receive a deduplicated