Teach mdmfs about tmpfs and use tmpfs in rc scripts

[Jia-Shiun Li]

On Fri, Mar 7, 2014 at 9:36 PM, Ian Lepore <ian at freebsd.org> wrote:
> I'm not sure what you mean.  If the device on the command line is md the
> program behaves as it always has.  If you ask for 'auto' you get the
> "best" memory filesystem available for some definition of "best".  If
> you don't trust someone else's definition of best (like you need failure
> at allocation time) then you choose the one that behaves the way you
> like.

ehh.. sorry read too fast and did not realize you 'added' new options
in addition to existing 'md'. My bad.

I did not use mdmfs often. My understanding is that it is the help to simplify
mdconfig-newfs-mount process to replace a one-step mount_mfs.
Then I agree with Konstantin, it does not look too appealing.
If the goal is to merge all memory-backed fs to single versatile command,
then the proposal does the job. Otherwise one mount_tmpfs comamnd does
all user needs for tmpfs, and I am not sure the auto decision is good if
user did not know what he need or care. It seems better to leave the decision
to user.

And for rc usage, I think we can just change it to tmpfs. If in the future tmpfs
grows ability to populate content with e.g. a cpio archive at boot time or
passed from command line, md usage can be further replaced.

-Jia-Shiun.