Xen devel - Oct 2005 - [PATCH 0/2] Change xs_read_watch interfaces to support variable arguments

The following set of changes modify the read_watch interface in 
userspace and in the kernel to support variable arguments.  This is in 
preparation for adding domid to @{introduce,release}Domain watches.  
This will allow backends to automatically reap on domain destruction 
which should eliminate a large number of the zombie problems we''re 
having on domain destruction since Xend no longer plays a role in 
freeing that memory.

The interface for read_watch is now consistent between userspace and 
kernel space.  It''s modelled after xs_read_directory.  The returned 
array is indexable via XS_WATCH_* macros.

While slightly awkward, IMHO it seems like the cleanest and most 
flexible option of the proposed interfaces.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori

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I should mention that I ran the xenstore testsuite (which rocks btw) and 
tested the block devices and network devices.  I haven''t tested blktap 
and vtpm but the changes are identical (and I don''t have any test cases
for those).

Regards,

Anthony Liguori

Anthony Liguori wrote:
> The following set of changes modify the read_watch interface in 
> userspace and in the kernel to support variable arguments.  This is in 
> preparation for adding domid to @{introduce,release}Domain watches.  
> This will allow backends to automatically reap on domain destruction 
> which should eliminate a large number of the zombie problems we''re
> having on domain destruction since Xend no longer plays a role in 
> freeing that memory.
>
> The interface for read_watch is now consistent between userspace and 
> kernel space.  It''s modelled after xs_read_directory.  The
returned
> array is indexable via XS_WATCH_* macros.
>
> While slightly awkward, IMHO it seems like the cleanest and most 
> flexible option of the proposed interfaces.
>
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
>
> Regards,
>
> Anthony Liguori
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>

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On Mon, Oct 03, 2005 at 11:43:43PM -0500, Anthony Liguori wrote:
> The following set of changes modify the read_watch interface in 
> userspace and in the kernel to support variable arguments.  This is in 
> preparation for adding domid to @{introduce,release}Domain watches.  
> This will allow backends to automatically reap on domain destruction 
> which should eliminate a large number of the zombie problems we''re
> having on domain destruction since Xend no longer plays a role in 
> freeing that memory.
Hi Anthony,

What you''ve done in your patch stands as a sensible thing on its own, I
think,
so I''m not objecting to that, but I am interested in why you think it
will
help with the zombies.  On domain destruction, xend is _supposed_ to remove
all the relevant entries of the store, and the backend drivers are _supposed_
to notice this and close themselves down.  If you have evidence that either of
those things aren''t happening, then we should regard that as a bug,
independent of your patch.  Have you seen that happening?

Ewan.

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Ewan Mellor wrote:
>On domain destruction, xend is _supposed_ to remove
>all the relevant entries of the store, and the backend drivers are
_supposed_
>to notice this and close themselves down.  If you have evidence that either
of
>those things aren''t happening, then we should regard that as a bug,
>independent of your patch.  Have you seen that happening?
>  
>
Hi Ewan,

I should have been more specific.  Zombie domains is a bug that 
frequently appears.  I''ve not seen it recently but it''s one of
those
things that frequently creeps into the tree.

Regards,

Anthony Liguori
>Ewan.
>
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.xensource.com
>http://lists.xensource.com/xen-devel
>
>  
>

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On Tue, Oct 04, 2005 at 09:34:43AM -0500, Anthony Liguori wrote:
> I should have been more specific.  Zombie domains is a bug that 
> frequently appears.  I''ve not seen it recently but it''s
one of those
> things that frequently creeps into the tree.
Good, that''s fine.  Hopefully there''ll be fewer creeping
zombies and a lot
more slaying from now on ;-)

Ewan.

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