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Re: Make vnd(4) work on sparse files

On Fri, Jun 24, 2011 at 04:13:14PM -0400, Thor Lancelot Simon wrote:
> On Fri, Jun 24, 2011 at 10:00:26PM +0200, J. Hannken-Illjes wrote:
> > ... this time with a diff attached:
> > 
> > With the attached diff vnd(4) devices will work on sparse files.
> > - Make the strategy decision a device flag and set to VNF_USE_VN_RDWR for
> >  files known to be sparse.
> What will the consumer of the vnd (in the important case, Xen, I suppose)
> see happen if there are no free blocks available when it writes into a
> hole?

the block device backen response can only be: BLKIF_RSP_EOPNOTSUPP,
allowed for a write, so the only possible solution is BLKIF_RSP_ERROR
(assuming the write to the vnd will return an error - which I really hope
it will do !)

Manuel Bouyer <>
     NetBSD: 26 ans d'experience feront toujours la difference

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