[Xen-devel] Re: Need help with fixing the Xen waitqueue feature

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 10/11/2011 04:29, "Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx> wrote:

>> The tools are supposed to catch ENOENT and try again.
>> linux_privcmd_map_foreign_bulk() does that. linux_gnttab_grant_map()
>> appears to do that as well. What code path uses qemu that leads to a
>> crash?
> 
> The tools retry as long as IOCTL_PRIVCMD_MMAPBATCH_V2 is supported. Which
> it isn't on mainline linux 3.0, 3.1, etc. Which dom0 kernel are you using?
> 
> And for backend drivers implemented in the kernel (netback, etc), there is
> no retrying.

Getting this working without a new Linux kernel -- and with
as-yet-to-be-written new stuff in it -- is unlikely to be on the cards is
it?

I think you suggested an in-kernel mechanism to wait for page-in and then
retry mapping. If that could be used by the in-kernel drivers and exposed
via our privcmd interface for qemu and rest of userspace too, that may be
the best single solution. Perhaps it could be largely hidden behind the
existing privcmd-mmap ioctls.

 -- Keir



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