Illumos 4891 - want zdb option to dump all metadata

4891 want zdb option to dump all metadata
Reviewed by: Sonu Pillai <sonu.pillai@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Garrett D'Amore <garrett@damore.org>

We'd like a way for zdb to dump metadata in a machine-readable
format, so that we can bring that back from a customer site for
in-house diagnosis.  Think of it as a crash dump for zpools,
which can be used for post-mortem analysis of a malfunctioning
pool

References:
  https://www.illumos.org/issues/4891
  https://github.com/illumos/illumos-gate/commit/df15e41

Porting notes:
- [cmd/zdb/zdb.c]
  - a5778ea zdb: Introduce -V for verbatim import
  - In main() getopt 'opt' variable removed and the code was
    brought back in line with illumos.
- [lib/libzpool/kernel.c]
  - 1e33ac1 Fix Solaris thread dependency by using pthreads
  - f0e324f Update utsname support
  - 4d58b69 Fix vn_open/vn_rdwr error handling
  - In vn_open() allocate 'dumppath' on heap instead of stack
  - Properly handle 'dump_fd == -1' error path
  - Free 'realpath' after added vn_dumpdir_code block

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

man/man8/zdb.8

@@ -11,7 +11,7 @@
 .\"
 .\"
 .\" Copyright 2012, Richard Lowe.
-.\" Copyright (c) 2012 by Delphix. All rights reserved.
+.\" Copyright (c) 2012, 2014 by Delphix. All rights reserved.
 .\"
 .TH "ZDB" "8" "February 15, 2012" "" ""
 
@@ -20,7 +20,7 @@
 
 .SH "SYNOPSIS"
 \fBzdb\fR [-CumdibcsDvhLMXFPA] [-e [-p \fIpath\fR...]] [-t \fItxg\fR]
-    [-U \fIcache\fR] [-I \fIinflight I/Os\fR]
+    [-U \fIcache\fR] [-I \fIinflight I/Os\fR] [-x \fIdumpdir\fR]
     [\fIpoolname\fR [\fIobject\fR ...]]
 
 .P
@@ -372,6 +372,20 @@ Operate on an exported pool, not present in \fB/etc/zfs/zpool.cache\fR. The
 \fB-p\fR flag specifies the path under which devices are to be searched.
 .RE
 
+.sp
+.ne 2
+.na
+\fB-x\fR \fIdumpdir\fR
+.ad
+.sp .6
+.RS 4n
+All blocks accessed will be copied to files in the specified directory.
+The blocks will be placed in sparse files whose name is the same as
+that of the file or device read.  zdb can be then run on the generated files.
+Note that the \fB-bbc\fR flags are sufficient to access (and thus copy)
+all metadata on the pool.
+.RE
+
 .sp
 .ne 2
 .na