Re: [PATCH/RFC 2.6.21 2/5] ehca: ehca_uverbs.c: "proper" use of mmap

Roland Dreier wrote on 11.01.2007 20:54:58:

 > >  int ehca_mmap(struct ib_ucontext *context, struct vm_area_struct

*vma)

 > >  {
 >
 > Can you split this monster routine into individual functions for
 > each type of mmap please?  With two helpers to get and verify the

cq/qp

 > shared by the individual sub-variants, that would also help to get rid
 > of all those magic offsets.
 >
 > Actually, this routine directly comes from ib_device.mmap - Roland,
 > can you shed some light on what's going on here?

Each userspace-accessible IB device gets a single device node like
/dev/infiniband/uverbsX.  Opening that gives userspace a "context".
One of the things userspace can do with that fd is mmap() on it --
that was originally envisioned as a way to map a page of hardware
registers directly in to the userspace process.

It seems ehca needs to allocate lots of different things in the kernel
via mmap().  What you're saying I guess is that ideally each of these
would be mmap() on a different fd rather than using different
offsets.  It's a little awkward to open multiple device nodes to get
multiple fds, since there's not a good way to attach them all to the
same context.  I guess we could create some hack to return more file
handles, but I think that cure is worse than the disease of using
magic offsets...

Maybe longer term we need to look at a scheme like cell's spufs but
I'm still not confident we have the RDMA interface quite ready to
freeze at the system call level.

 - R.

...as Roland mentions, we're not completely free to change the filehandle
usage,
it's shared by ~5 drivers now.

I'd say lets investigate the direction of an own filesystem unless
there's no other clean solution.
We can polish the current version a bit, but that won't change the "magic
offsets".

Roland, could you take this patchset into your tree?
We hope it adresses the major security concern and vm_insert_page.

We're preparing the next patch for the yield deadlock topic with this
patchset as prereq.

Gruss / Regards . . . Christoph Raisch