IRC, freenode, #hurd, 2011-10-15
<antrik> youpi: I'm not at all talking about ordinary tmpfs. I'm talking
about the proposed variant using a separate backing store
<antrik> youpi: and as you might remember, I once came up with a crazy
passive translator command line (based on another crazy passive
translator command line from tschwinge) that can automatically do the
<antrik> so there is really very little benefit in using something else
than ext2fs when not paging to the swap partition
<antrik> real tmpfs IMHO is mostly useful precisely because it uses the
ordinary swap, and doesn't have an explicit size limit...
<youpi> well, it is still quite a waste to bounce data betwen page cache
and memory storage
<youpi> or is ext2fs able to map the store data directly?
<youpi> then there's only the medata bounce which is spurious
<youpi> and still, even a one-liner settrans doesn't fit with the "is just
an fs alternative for the existing tmpfs-mounting scripts"
<antrik> youpi: well, if the invocation is the major concern, it would be
trivial to write a tiny wrapper binary or script that acts like a
<youpi> antrik: could you write it then?
<antrik> you mean a shell script that uses ext2fs on a memory store to act
like a "proper" tmpfs?
<youpi> I mean whatever that permits to just run mount none /tmp -t tmpfs
<youpi> and just works already nowadays
<youpi> which we could e.g. ship instead of our currently-completely bugged
<antrik> I suspect the mount script just looks for /hurd/tmpfs in this
case? if so, that should indeed be pretty trivial. let's see if I can dig
up my crazy command line -- turning that into a "proper" script should be
quite easy I hope...
<antrik> hm... I digged up
http://lists.gnu.org/archive/html/bug-hurd/2007-04/msg00013.html ; but I
wonder how much of it is really necessary for a generic pseudo-tmpfs...
<antrik> the major complication seems to be the chmod, which I guess we
don't need for most use cases...
<youpi> I actually don't see why it's inlined there
<youpi> doesn't the caller do it if it needs it?
<youpi> ah, well, here there is no caller, it's just a passive entry
<antrik> is it a problem that this solution needs an extra node for the
<youpi> because you need to say where it resides
<youpi> and there's no safe place
<youpi> since such safe place would typically be a mounted tmpfs
<antrik> I feared that much...
<antrik> I suspect we could work around this by not attaching the store to
any node; but this a) doesn't work in a shell script, and b) is much more
<antrik> hm... can we assume /dev/fd to be present? I have a vague crazy
<antrik> I consider hacking settrans so it grows an option which allows
passing the port to the translator as an FD, instead of attaching it to
any node... this way, we could work with anonymous translators in shell
<antrik> (of course that's not less work than just doing the wrapper in
C... but it could be useful in other cases)