I have to allow non-root users to mount a CD-ROMs(CD9660, UDF) and
diskettes (MSDOSFS) filesystems.

I've set vfs.usermount to 1, changed permissions of devices in
/etc/devfs.conf, permissions of mount points - everything according to
FreeBSD faq #9.22.

But our users speak Russian and use CD-ROM/diskettes with Cyrillic
letters in filenames and I've added corresponding options to /etc/fstab
/dev/acd0 /cdrom cd9660  ro,noauto,-CUTF-8 0 0
(users use KDE so their locale is ru_RU.UTF-8).

And this option made impossible for users to mount cdrom!

Because it loads kiconv charset translation table that is allowed to
root only.  Searching internet showed a common solution to this problem
is creating small startup script in /usr/local/etc/rc.d with mount/umount
commands only:

  #!/bin/sh
  mount /cdrom
  umount /cdrom

Besides ugly error messages on console this script increases boot time.

So I've written this little utility that loads the charset conversion tables.
IMHO, it could be useful for many other people. And it's worth to include it in FreeBSD.

Script loadfscharsets should be placed in /etc/rc.d/.
Script expects next variables in /etc/rc.conf:

loadfscharsets_enabled={YES|NO}
loadfscharsets_fstypes={list of filesystems that use kiconv filename translation, defaults to "cd9660 udf msdosfs"}
loadfscharsets_cspairs={list of charset pairs|Russian|Japanese}

loadfscharsets_fstypes specifies list of filesystem types that use
external kernel modules for file name translation.

The kernel module <filesystem type name>_iconv have to exist in
/boot/kernel directory.

loadfscharsets_cspairs could be list of charsets pairs like UTF-8 (which
is equal to UTF-8:UTF-16BE), UTF-8:CP866, eucJP:CP932 or words like
Russian (equal to "UTF-8 UTF-8:CP866" list), Japanese (equal to
"UTF-8 UTF-8:CP92), some locale names (ru_RU.UTF-8, ru_RU.KOI-8 etc)

How-To-Repeat: After boot:
root# sysctl vfs.usermount=1
root# chown user /dev/acd0
root# chown user /cdrom
root# su user
user$ mount_cd9660 -CUTF-8 /dev/acd0 /cdrom
mount_cd9660: cd9660_iconv: Operation not permitted
root# mount_cd9660 -CUTF-8 /dev/acd0 /cdrom
root# umount /cdrom
user$ mount_cd9660 -CUTF-8 /dev/acd0 /cdrom
user$ mount | fgrep cdrom
/dev/acd0 on /cdrom (cd9660, local, nosuid, read-only, mounted by user)