Add ability to scrub from last scrubbed txg

Some users might want to scrub only new data because they would like
to know if the new write wasn't corrupted.  This PR adds possibility
scrub only newly written data.

This introduces new `last_scrubbed_txg` property, indicating the
transaction group (TXG) up to which the most recent scrub operation
has checked and repaired the dataset, so users can run scrub only
from the last saved point. We use a scn_max_txg and scn_min_txg
which are already built into scrub, to accomplish that.

Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mariusz Zaborski <mariusz.zaborski@klarasystems.com>
Sponsored-By: Wasabi Technology, Inc.
Sponsored-By: Klara Inc.
Closes #16301

man/man8/zpool-scrub.8

@@ -26,7 +26,7 @@
 .\" Copyright 2017 Nexenta Systems, Inc.
 .\" Copyright (c) 2017 Open-E, Inc. All Rights Reserved.
 .\"
-.Dd June 22, 2023
+.Dd November 18, 2024
 .Dt ZPOOL-SCRUB 8
 .Os
 .
@@ -36,9 +36,8 @@
 .Sh SYNOPSIS
 .Nm zpool
 .Cm scrub
-.Op Fl s Ns | Ns Fl p
+.Op Ns Fl e | Ns Fl p | Fl s Ns | Fl C Ns
 .Op Fl w
-.Op Fl e
 .Ar pool Ns …
 .
 .Sh DESCRIPTION
@@ -114,6 +113,10 @@ The pool must have been scrubbed at least once with the
 feature enabled to use this option.
 Error scrubbing cannot be run simultaneously with regular scrubbing or
 resilvering, nor can it be run when a regular scrub is paused.
+.It Fl C
+Continue scrub from last saved txg (see zpool
+.Sy last_scrubbed_txg
+property).
 .El
 .Sh EXAMPLES
 .Ss Example 1