[Bug 271352] "live" dump -- with a snapshot -- broken by recent upgrade

From: <bugzilla-noreply_at_freebsd.org>
Date: Wed, 10 May 2023 15:10:05 UTC 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=271352

            Bug ID: 271352
           Summary: "live" dump -- with a snapshot -- broken by recent
                    upgrade
           Product: Base System
           Version: Unspecified
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: mi@ALDAN.algebra.com

For years now the nightly dumps of /home were running here from cron:

exec lockf -t 0 /tmp/home-dump-lock dump 0uaCLf 16 - /home | .....

After upgrading to the 13-stable as of May 5th (after 265 days of uptime), that
job started failing with:

  DUMP: Date of this level 0 dump: Wed May 10 10:58:00 2023
  DUMP: Date of last level 0 dump: the epoch
  DUMP: Dumping snapshot of /dev/ada0h (/home) to standard output
dump: Cannot find file system superblock: No such file or directory

(Note, that the file system is happily mounted and in use.)

Rerunning the same command without the "L" switch works (with a warning):

  DUMP: WARNING: should use -L when dumping live read-write filesystems!
  DUMP: Date of this level 0 dump: Wed May 10 10:58:07 2023
  DUMP: Date of last level 0 dump: the epoch
  DUMP: Dumping /dev/ada0h (/home) to standard output
  DUMP: mapping (Pass I) [regular files]
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 57211585 tape blocks.
  DUMP: dumping (Pass III) [directories]
  DUMP: dumping (Pass IV) [regular files]
...

Seems like something is broken about the snapshot-creation. The /home/.snap
exists -- and is empty... The machine has 32Gb of RAM, and /home is only about
13% full at present:

root@symbion:~ # df -m /home
Filesystem 1M-blocks  Used  Avail Capacity  Mounted on
/dev/ada0h    458392 56009 365711    13%    /home
root@symbion:~ # tunefs -p /dev/ada0h
tunefs: POSIX.1e ACLs: (-a)                                disabled
tunefs: NFSv4 ACLs: (-N)                                   disabled
tunefs: MAC multilabel: (-l)                               disabled
tunefs: soft updates: (-n)                                 enabled
tunefs: soft update journaling: (-j)                       disabled
tunefs: gjournal: (-J)                                     disabled
tunefs: trim: (-t)                                         enabled
tunefs: maximum blocks per file in a cylinder group: (-e)  4096
tunefs: average file size: (-f)                            16384
tunefs: average number of files in a directory: (-s)       64
tunefs: minimum percentage of free space: (-m)             8%
tunefs: space to hold for metadata blocks: (-k)            2600
tunefs: optimization preference: (-o)                      time
tunefs: volume label: (-L)                                 home

I recall it being formatted as UFS1 -- but don't know, how to ascertain that.

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