newfs: Add an option to disable soft updates

[des]

Summary

A previous commit turned soft updates on by default for UFS2 without
providing a way to turn them off. This corrects that by adding a new -u
flag which forces soft updates (and soft updates journaling) off.

MFC after: 1 week
Sponsored by: Klara, Inc.
Sponsored by: NetApp, Inc.
Fixes: 61dece6d27fb ("Enable soft updates by default for UFS2 filesystems.")

[mckusick]

You do not specify what happens if both -U and -u are specified. In practice, whichever one is second wins out. I think it should be flagged as an error.

sbin/newfs/newfs.8

101–115

You have this same sentence twice. I suggest deleting this first instance of it.

[des]

In D54576#1247249, @mckusick wrote:

You do not specify what happens if both -U and -u are specified. In practice, whichever one is second wins out. I think it should be flagged as an error.

That is deliberate and consistent with other utilities. For instance, df does not error out if you specify more than one of -k, -m, -g, -h, but simply obeys whichever one was specified last.

sbin/newfs/newfs.8

101–115

The duplication is deliberate and consistent with our other manual pages.

[mckusick]

sbin/newfs/newfs.8

101–115

Give me an example where the same sentence appears with just one short sentence between it. This reads horribly.

[des]

sbin/newfs/newfs.8

101–115

It reads horribly in the mandoc source, but less so in the rendered result:

-U      Enable soft updates on the new file system.  If neither -U nor -u
        is specified, soft updates are enabled by default for UFS2 format
        file systems and disabled otherwise.

-u      Do not enable soft updates on the new file system.  If neither -U
        nor -u is specified, soft updates are enabled by default for UFS2
        format file systems and disabled otherwise.

Again, compare with df(1), which repeats “This overrides any BLOCKSIZE specification from the environment” for every option for which that applies.