Re: losetuping files in tmpfs fails?

[Andrew Morton <akpm@zip.com.au>]

Andy Gaynor wrote:
> 
> 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.
> 
> ...
>   /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 >

Yup, tmpfs doesn't provide some of the facilities which the
loop driver requires.   Specifically, prepare_write() and 
commit_write().  

Probably it's not too hard to change loop to use generic_file_write(),
and it will then permit tmpfs file-backed loop mounts.

It's not obvious that there's a burning need to support loop-on-tmpfs
though, is there?

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