Add `zstream redup` command to convert deduplicated send streams

Deduplicated send and receive is deprecated.  To ease migration to the
new dedup-send-less world, the commit adds a `zstream redup` utility to
convert deduplicated send streams to normal streams, so that they can
continue to be received indefinitely.

The new `zstream` command also replaces the functionality of
`zstreamdump`, by way of the `zstream dump` subcommand.  The
`zstreamdump` command is replaced by a shell script which invokes
`zstream dump`.

The way that `zstream redup` works under the hood is that as we read the
send stream, we build up a hash table which maps from `<GUID, object,
offset> -> <file_offset>`.

Whenever we see a WRITE record, we add a new entry to the hash table,
which indicates where in the stream file to find the WRITE record for
this block. (The key is `drr_toguid, drr_object, drr_offset`.)

For entries other than WRITE_BYREF, we pass them through unchanged
(except for the running checksum, which is recalculated).

For WRITE_BYREF records, we change them to WRITE records.  We find the
referenced WRITE record by looking in the hash table (for the record
with key `drr_refguid, drr_refobject, drr_refoffset`), and then reading
the record header and payload from the specified offset in the stream
file.  This is why the stream can not be a pipe.  The found WRITE record
replaces the WRITE_BYREF record, with its `drr_toguid`, `drr_object`,
and `drr_offset` fields changed to be the same as the WRITE_BYREF's
(i.e. we are writing the same logical block, but with the data supplied
by the previous WRITE record).

This algorithm requires memory proportional to the number of WRITE
records (same as `zfs send -D`), but the size per WRITE record is
relatively low (40 bytes, vs. 72 for `zfs send -D`).  A 1TB send stream
with 8KB blocks (`recordsize=8k`) would use around 5GB of RAM to
"redup".

Reviewed-by: Jorgen Lundman <[email protected]>
Reviewed-by: Paul Dagnelie <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Matthew Ahrens <[email protected]>
Closes #10124 
Closes #10156 

1 files changed, 61 insertions, 0 deletions

diff --git a/cmd/zstream/zstream.c b/cmd/zstream/zstream.c
new file mode 100644
index 000000000..95578c97c
--- /dev/null
+++ b/cmd/zstream/zstream.c
@@ -0,0 +1,61 @@
+/*
+ * CDDL HEADER START
+ *
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * http://www.illumos.org/license/CDDL.
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2020 by Delphix. All rights reserved.
+ */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <strings.h>
+#include <unistd.h>
+#include <libintl.h>
+#include <stddef.h>
+#include <libzfs.h>
+#include "zstream.h"
+
+void
+zstream_usage(void)
+{
+	(void) fprintf(stderr,
+	    "usage: zstream command args ...\n"
+	    "Available commands are:\n"
+	    "\n"
+	    "\tzstream dump [-vCd] FILE\n"
+	    "\t... | zstream dump [-vCd]\n"
+	    "\n"
+	    "\tzstream redup [-v] FILE | ...\n");
+	exit(1);
+}
+
+int
+main(int argc, char *argv[])
+{
+	if (argc < 2)
+		zstream_usage();
+
+	char *subcommand = argv[1];
+
+	if (strcmp(subcommand, "dump") == 0) {
+		return (zstream_do_dump(argc - 1, argv + 1));
+	} else if (strcmp(subcommand, "redup") == 0) {
+		return (zstream_do_redup(argc - 1, argv + 1));
+	} else {
+		zstream_usage();
+	}
+}