losetuping files in tmpfs fails?

[Andy Gaynor <silver@silver.unix-fu.org>]

Whilst trying to figure out why my dang stripes won't persist (a separate
but worrisome issue), I wrote a dittie which creates a couple junk files in
/tmp (tmpfs), associates loop devices with them, whoops, losetup craps out.

  /home/root# losetup -d /dev/loop/5 2>/dev/null # Free /dev/loop/5

  /home/root# cd /home/root             # Go home
  /home/root# mount | grep /home        # Filesystem is ...
  /dev/md/8 on /home type reiserfs (rw) #   reiserfs
  /home/root# echo foo > foo            # Create file foo
  /home/root# losetup /dev/loop/5 foo   # Give foo to /dev/loop/5
  /home/root# losetup -d /dev/loop/5    # Free /dev/loop/5
  /home/root# rm foo                    # Remove foo

  /home/root# cd /tmp                   # Go to /tmp
  /tmp# mount | grep tmp                # Filesystem is ...
  tmpfs on /tmp type tmpfs (rw)         #   tmpfs
  /tmp# echo foo > foo                  # Create file foo
  /tmp# losetup /dev/loop/5 foo         # Give foo to /dev/loop/5
  ioctl: LOOP_SET_FD: Invalid argument  #   DISCO!!!                <o >  <o >
  /tmp# rm foo                          # Remove foo

    Version information:

  Distribution: Debian Woody, up-to-date as of a week ago
  Kernel: Linux 2.4.17

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Regards, [Ag]   Andy Gaynor   silver@silver.unix-fu.org