I take the blame for that one. I added the hook because, if a process 
were to die whilst holding one or more grants, there were no hooks that 
would make it possible to carry out the grant-unmap. All existing hooks 
on either the device or the VMA were called *after* the PTEs were cleared.

It gets better, though. The same hook is used in the version of blktap 
in linux-2.6.18-xen (not, as far as I can see, in the sparse tree for 
xen-3.1-testing):
 
http://xenbits.xensource.com/linux-2.6.18-xen.hg?file/fd879c0688bf/drivers/xen/blktap/blktap.c

Reverting back to the old (hookless) behaviour would be a retrograde 
step IMHO.

Cheers,

Derek Murray.

Gerd Hoffmann wrote:

Stephen C. Tweedie wrote:

quoted

Hi all,

  driver domains

Looked at the gntdev (grant table mappings for user space) driver,
noticed that one is not self-contained.  It needs a hook for page unmapping:

  http://xenbits.xensource.com/xen-3.1-testing.hg?rev/7180d2e61f92
  plus an s/ptep_get_and_clear_full/zap_pte/ fixup a few changesets
  later.

Upstreaming that one could become *uhm* intresting.  Nevertheless the
gntdev functionality is quite useful for writing pure userspace
backend drivers ...

cheers,
  Gerd

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