Re: bin/60383: fssconfig(8): distinguish between taking and loading a snapshot

The following reply was made to PR bin/60383; it has been noted by GNATS.

From: Taylor R Campbell <[email protected]>
To: [email protected], [email protected]
Cc: Robert Elz <[email protected]>
Subject: Re: bin/60383: fssconfig(8): distinguish between taking and loading a snapshot
Date: Sat, 25 Jul 2026 19:28:30 +0000

 Another thing that would be nice: mount a snapshot -- or any file
 system, really -- just for the duration of a command, so that you
 could, e.g., easily write a cron job that rsyncs a snapshot without
 having to teach rsync(1) (or tar(1) or tarsnap(1) or borg(1) or
 whatever) how to create snapshots on NetBSD:
 
 	withsnapmount /fs /fs/.snap/snapname /mnt \
 	rsync -aH /mnt/. backuphost:/backups/$(hostname)/.
 
 (How to distinguish taking a new snapshot from loading an existing
 snapshot in this operation is left as an exercise for the reader's
 imagination.)
 
 
 
 Also, for comparison, here's the interface on FreeBSD:
 
 1. Create a snapshot /fs/.snap/snapname of the file system /fs
    (assuming that is, in fact, the mount point) using the
    mksnap_ffs(8) command:
 
 	# mksnap_ffs /fs/.snap/snapname
 
 2. Create a snapshot /fs/.snap/snapname of the file system /fs, using
    the mount(8) command -- but this doesn't actually mount it,
    apparently:
 
 	# mount -u -o snapshot /fs/.snap/snapname /fs
 
 3. Given a snapshot that was previously created, mount it at /mnt:
 
 	# mdconfig -a -t vnode -o readonly -f /fs/.snap/snapname -u 4
 	# mount -r /dev/md4 /mnt
 
 Except for mksnap_ffs(8), this strikes me as very confusing!  I'm not
 sure we want to copy it.
 
 https://web.archive.org/web/20260722195637/https://docs.freebsd.org/en/book=
 s/handbook/disks/#snapshots
 https://web.archive.org/web/20251118192326/https://man.freebsd.org/cgi/man.=
 cgi?query=3Dmksnap_ffs&sektion=3D8&format=3Dhtml
 https://web.archive.org/web/20260220073336/https://man.freebsd.org/cgi/man.=
 cgi?format=3Dhtml&query=3Dmount&sektion=3D8