zdb: add -B option to generate backup stream

This is more-or-less like `zfs send`, but specifying the snapshot by its objset id for situations where it can't be referenced any other way. Sponsored-By: Klara, Inc. Signed-off-by: Rob Norris <[email protected]>
openzfs · Mar 21, 2023 · 4933fb9 · 4933fb9
1 parent fa46802
commit 4933fb9
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Showing 2 changed files with 112 additions and 4 deletions.
diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
@@ -789,6 +789,9 @@ usage(void)
 	    "\t\t[<poolname>[/<dataset | objset id>] [<object | range> ...]]\n"
 	    "\t%s [-AdiPv] [-e [-V] [-p <path> ...]] [-U <cache>] [-K <key>]\n"
 	    "\t\t[<poolname>[/<dataset | objset id>] [<object | range> ...]\n"
+	    "\t%s -B [-e [-V] [-p <path> ...]] [-I <inflight I/Os>]\n"
+	    "\t\t[-o <var>=<value>]... [-t <txg>] [-U <cache>] [-x <dumpdir>]\n"
+	    "\t\t[-K <key>] <poolname>/<objset id> [<backupflags>]\n"
 	    "\t%s [-v] <bookmark>\n"
 	    "\t%s -C [-A] [-U <cache>]\n"
 	    "\t%s -l [-Aqu] <device>\n"
@@ -802,7 +805,7 @@ usage(void)
 	    "\t%s -S [-AP] [-e [-V] [-p <path> ...]] [-U <cache>] "
 	    "<poolname>\n\n",
 	    cmdname, cmdname, cmdname, cmdname, cmdname, cmdname, cmdname,
-	    cmdname, cmdname, cmdname, cmdname);
+	    cmdname, cmdname, cmdname, cmdname, cmdname);
 
 	(void) fprintf(stderr, "    Dataset name must include at least one "
 	    "separator character '/' or '@'\n");
@@ -825,6 +828,8 @@ usage(void)
 	(void) fprintf(stderr, "    Options to control amount of output:\n");
 	(void) fprintf(stderr, "        -b --block-stats             "
 	    "block statistics\n");
+	(void) fprintf(stderr, "        -B --backup                  "
+	    "backup stream\n");
 	(void) fprintf(stderr, "        -c --checksum                "
 	    "checksum all metadata (twice for all data) blocks\n");
 	(void) fprintf(stderr, "        -C --config                  "
@@ -4866,6 +4871,81 @@ dump_path(char *ds, char *path, uint64_t *retobj)
 	return (err);
 }
 
+static int
+dump_backup_bytes(objset_t *os, void *buf, int len, void *arg)
+{
+	const char *p = (const char *)buf;
+	ssize_t nwritten;
+
+	(void) os;
+	(void) arg;
+
+	/* Write the data out, handling short writes and signals. */
+	while ((nwritten = write(STDOUT_FILENO, p, len)) < len) {
+		if (nwritten < 0) {
+			if (errno == EINTR)
+				continue;
+			return (errno);
+		}
+		p += nwritten;
+		len -= nwritten;
+	}
+
+	return (0);
+}
+
+static void
+dump_backup(const char *pool, uint64_t objset_id, const char *flagstr)
+{
+	boolean_t embed = B_FALSE;
+	boolean_t large_block = B_FALSE;
+	boolean_t compress = B_FALSE;
+	boolean_t raw = B_FALSE;
+
+	const char *c;
+	for (c = flagstr; c != NULL && *c != '\0'; c++) {
+		switch (*c) {
+			case 'e':
+				embed = B_TRUE;
+				break;
+			case 'L':
+				large_block = B_TRUE;
+				break;
+			case 'c':
+				compress = B_TRUE;
+				break;
+			case 'w':
+				raw = B_TRUE;
+				break;
+			default:
+				fprintf(stderr, "dump_backup: invalid flag "
+				    "'%c'\n", *c);
+				return;
+		}
+	}
+
+	if (isatty(STDOUT_FILENO)) {
+		fprintf(stderr, "dump_backup: stream cannot be written "
+		    "to a terminal\n");
+		return;
+	}
+
+	offset_t off = 0;
+	dmu_send_outparams_t out = {
+	    .dso_outfunc = dump_backup_bytes,
+	    .dso_dryrun  = B_FALSE,
+	};
+
+	int err = dmu_send_obj(pool, objset_id, /* fromsnap */0, embed,
+	    large_block, compress, raw, /* saved */ B_FALSE, STDOUT_FILENO,
+	    &off, &out);
+	if (err != 0) {
+		fprintf(stderr, "dump_backup: dmu_send_obj: %s\n",
+		    strerror(err));
+		return;
+	}
+}
+
 static int
 zdb_copy_object(objset_t *os, uint64_t srcobj, char *destfile)
 {
@@ -8651,6 +8731,7 @@ main(int argc, char **argv)
 	struct option long_options[] = {
 		{"ignore-assertions",	no_argument,		NULL, 'A'},
 		{"block-stats",		no_argument,		NULL, 'b'},
+		{"backup",		no_argument,		NULL, 'B'},
 		{"checksum",		no_argument,		NULL, 'c'},
 		{"config",		no_argument,		NULL, 'C'},
 		{"datasets",		no_argument,		NULL, 'd'},
@@ -8692,10 +8773,11 @@ main(int argc, char **argv)
 	};
 
 	while ((c = getopt_long(argc, argv,
-	    "AbcCdDeEFGhiI:kK:lLmMNo:Op:PqrRsSt:uU:vVx:XYyZ",
+	    "AbBcCdDeEFGhiI:kK:lLmMNo:Op:PqrRsSt:uU:vVx:XYyZ",
 	    long_options, NULL)) != -1) {
 		switch (c) {
 		case 'b':
+		case 'B':
 		case 'c':
 		case 'C':
 		case 'd':
@@ -9029,7 +9111,8 @@ main(int argc, char **argv)
 				    checkpoint_pool, error);
 			}
 
-		} else if (target_is_spa || dump_opt['R'] || objset_id == 0) {
+		} else if (target_is_spa || dump_opt['R'] || dump_opt['B'] ||
+		    objset_id == 0) {
 			zdb_set_skip_mmp(target);
 			error = spa_open_rewind(target, &spa, FTAG, policy,
 			    NULL);
@@ -9165,7 +9248,10 @@ main(int argc, char **argv)
 					    strerror(errno));
 			}
 		}
-		if (os != NULL) {
+		if (dump_opt['B']) {
+			dump_backup(target, objset_id,
+			    argc > 0 ? argv[0] : NULL);
+		} else if (os != NULL) {
 			dump_objset(os);
 		} else if (zopt_object_args > 0 && !dump_opt['m']) {
 			dump_objset(spa->spa_meta_objset);

diff --git a/man/man8/zdb.8 b/man/man8/zdb.8
@@ -41,6 +41,13 @@
 .Ar poolname Ns Op Ar / Ns Ar dataset Ns | Ns Ar objset-ID
 .Op Ar object Ns | Ns Ar range Ns …
 .Nm
+.Fl B
+.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
+.Op Fl U Ar cache
+.Op Fl K Ar key
+.Ar poolname Ns Ar / Ns Ar objset-ID
+.Op Ar backup-flags
+.Nm
 .Fl C
 .Op Fl A
 .Op Fl U Ar cache
@@ -123,6 +130,21 @@ Display options:
 Display statistics regarding the number, size
 .Pq logical, physical and allocated
 and deduplication of blocks.
+.It Fl B , -backup
+Generate a backup stream, similar to
+.Nm zfs Cm send ,
+but for the numeric objset ID, and without opening the snapshot.
+This is useful if the snapshot metadata has become corrupted.
+The optional
+.Ar flags
+argument is a string of one or more of the letters
+.Sy e ,
+.Sy L ,
+.Sy c ,
+and
+.Sy w ,
+which correspond to the same flags in
+.Xr zfs-send 8 .
 .It Fl c , -checksum
 Verify the checksum of all metadata blocks while printing block statistics
 .Po see