mounted snapshots still writeable 1.5 years later (RE: kern/68576)

[John Kozubik]

In July of 2004 (circa 5.2.1-RELEASE) I filed kern/68576 which described
how snapshot files can be mounted read/write and altered.  New files can
be added to them, existing files can be deleted or altered, and the
snapshot file can be returned to read-only state and still be used.

It was generally agreed that this was a bad thing - it is unexpected
behavior that contradicts the technical requirements of UFS2 snapshots as
well as the behavior that the FreeBSD documentation provides.  It is also
potentially dangerous.

It is now Nov. 2005, circa 5.4-RELEASE, and the behavior described in this
PR has not changed.

-----
John Kozubik - john at kozubik.com - http://www.kozubik.com