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Date: Mon, 25 Aug 1997 02:28:50 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199708241628.CAA16264@godzilla.zeta.org.au>
To: bde@zeta.org.au, current@FreeBSD.ORG
Subject: Re: another mount arg incompatibility
Sender: owner-freebsd-current@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

I wrote:
>After `mount -t msdos /dev/fd0 /mnt' (which works and gives a mode of
>root.wheel for the mount point), `mount -t msdos -o '' /dev/fd0 /mnt'
>changes the mode to 4022327920.8338.

I should have written:
After `mount -t msdos /dev/fd0 /mnt' (which works and gives ownership of
root.wheel for the mount point), `mount -u -o '' /dev/fd0 /mnt'
changes the ownership to 4022327920.8338.

`mount -u -t msdos ...' fails early because mount_msdos doesn't support
the MNT_UPDATE flag although msdosfs sort of supports it.  Support for
MNT_FORCE is similarly broken.  Support for MNT_SYNCHRONOUS is slightly
more broken - it is a general vfs flag (it mainly affects vn_write(), so
it belongs in MNT_STD more that some of the other options in MNT_STD
(it doesn't apply to inherently readonly file systems, but neither does
MNT_NOATIME, and support for quotas is not standard...).  Perhaps the
support shouldn't be limited in individual mount utilities.  However,
many kernel mount routines just ignore unsupported flags.

`mount -u -o '' /dev/fd0 /mnt' is immune to the above problem because
mount(8) calls mount(2) directly.  mount(2) somehow gets as far as
msdosfs_mount().  msdosfs_mount() then uses invalid mount args.

Another bug: after

	`mount -t msdos /dev/fd0 /mnt'		#works
	`mount -t ext2fs /dev/wd0s1 /mnt'	#works?

it seems to be impossible to unmount either file system.

Bruce