Questions on mmap()

["Martin Frey" <frey@scs.ch>]

Dear all,

I'm trying to write an example on how to export kmalloc()
and vmalloc() allocated areas from a device driver into
user space. The example is running so far, but I want to
make sure to have all the details right.

So here I have couple of questions:
- for kmalloc, I just call remap_page_range() in my drivers
  mmap method. Do I have to grab any locks before doing
  so (kernel 2.4.x), e.g. big kernel lock?
- Do I have to set any flags in vm_area_struct->vm_flags?
  I see some drivers setting VM_LOCKED while others don't.
  As far as I understand the kernel will try to swap the
  area out starting in swp_out_mm, calling swp_out_vma.
  If VM_LOCKED I will return if VM_LOCKED is set. If not,
  I will fall into swap_out_pXX until I finally hit
  the reserve bit of the page that should go out.
  If I understand the code right, setting VM_LOCKED is
  not necessary, I will be safe without. But performancewise
  have VM_LOCKED set will make me fall out of the swap-out
  attempt earlier. Is this correct?
- To map a vmalloc() allocated area, I set up my own
  page fault handler (vm_ops). Again, are any flags
  needed in the vm_flags field?
- In my pagefault handler I parse the pagetables as e.g.
  done in uvirt_to_kva in the bttv-driver. Do I need
  to grab a lock before doing so? 
- What is the purpose and usage of the VMALLOC_VMADDR
  macro?

Any help is appreciated.

Thanks and best regards,

Martin Frey

-- 
Supercomputing Systems AG       email: frey@scs.ch
Martin Frey                     web:   http://www.scs.ch/~frey/
at Compaq Computer Corporation  phone: +1 603 884 4266
ZKO2-3N25, 110 Spit Brook Road, Nashua, NH 03062

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