[dbolgheroni]

OpenBSD uses vnconfig (also FreeBSD; on NetBSD it's vndconfig). An example:

  # vnconfig vnd0 install63.fs

Then you can treat vnd0 as if it was a disk:

  # disklabel vnd0
  # /dev/rvnd0c:
  type: vnd
  disk: vnd device
  label: fictitious
  duid: 138b4f2a2e184426
  flags:
  bytes/sector: 512
  sectors/track: 100
  tracks/cylinder: 1
  sectors/cylinder: 100
  cylinders: 7382
  total sectors: 738240
  boundstart: 1024
  boundend: 737280
  drivedata: 0 
  
  16 partitions:
  #                size           offset  fstype [fsize bsize   cpg]
    a:           736256             1024  4.2BSD   2048 16384 16142 
    c:           738240                0  unused                    
    i:              960               64   MSDOS                    

For instance, to mount the 'a' partition:

  # mount /dev/vnd0a /mnt

You can also associate an encryption key with the device. All data written to the diskimage will then be encrypted.

[floatboth]

FreeBSD does not use vnconfig, FreeBSD uses mdconfig:

    # mdconfig -f smartos-latest-USB.img
    md0
    # gpart list md0
    ...
    scheme: MBR
    Providers:
    1. Name: md0s1
       ...
    # mount -o ro -t msdosfs /dev/md0s1 /mnt
    // (or, use labels)
    # mount -o ro -t msdosfs /dev/msdosfs/SMARTOSBOOT /mnt

Or for ISOs, in one line:

    # mount -t cd9660 /dev/$(mdconfig -f image.iso) /mnt

[jlgaddis]

I was just about to correct your correction, because I can quite clearly recall using vnconfig on FreeBSD.

Apparently that's been a little while, however. According to vnconfig(8):

> The mdconfig utility first appeared in FreeBSD 5.0 as a cleaner replacement for the vn(4) and vnconfig(8) combo.

5.0 was released just over 15 years ago.