Re: bin/57903: umount: Add -d option to umount to detach vnode device

["Robert Elz via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR bin/57903; it has been noted by GNATS.

From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: bin/57903: umount: Add -d option to umount to detach vnode device
Date: Thu, 27 Mar 2025 14:43:33 +0700

     Date:        Thu, 27 Mar 2025 01:10:02 +0000 (UTC)
     From:        "David H. Gutteridge via gnats" <gnats-admin%NetBSD.org@localhost>
     Message-ID:  <20250327011002.3F5411A923D%mollari.NetBSD.org@localhost>
 
   |  It would need to walk backwards from the mounted structure to find the
   |  vnd that originally made it available. (And only unconfigure if there
   |  are no other mount points in use, of course.)
 
 Another reason for a generic ioctl for all devices, wedges could use it
 to remove themselves, and then pass the same ioctl back to its parent
 device, if that also unconfigures itself, it does the same to its parent.
 Once some device/file which does not understand the ioctl is reached,
 it all just stops (and providing at least something was unconfigured,
 succeeds).
 
 An entirely plausible setup is to have a GPT partition in a cgd living in
 a vnd in a file on the filesystem.   And even more than vnd's where it is
 no more than a slight convenience, I'd think unconfiguring a cgd once it
 is no longer mounted would be a much more desirable goal.
 
 kre