Re: [dm-devel] [ovirt-devel] blockdev --flushbufs required [was: parted issue/question

[Mike Burns <mburns redhat com>]

Thanks Jim

Moving to correct ovirt-node mailing list (node-devel ovirt org)

On Wed, 2012-01-18 at 14:44 +0100, Jim Meyering wrote:
> [Following up on this thread:
>  http://thread.gmane.org/gmane.linux.kernel.device-mapper.devel/14999]
> 
> Alasdair G Kergon wrote:
> > Try
> >   blkdev --flushbufs
> > after any cmd that writes to a dev to see if that makes any difference.
> 
> Thanks for the work-around.
> Using "blockdev --flushbufs $dev" does indeed make parted
> behave the same with dm-backed storage as with other devices.
> 
> Adjusting my small example,
> 
>   cd /tmp; truncate -s 10m g && loop=$(losetup --show -f g)
>   echo 0 100 linear $loop 0 | dmsetup create zub
>   dev=/dev/mapper/zub
>   parted -s $dev \
>     mklabel gpt \
>     mkpart efi 34s 34s \
>     mkpart root 35s 35s \
>     mkpart roo2 36s 36s \
>     u s p
>   blockdev --flushbufs $dev # FIXME: required with device-mapper-1.02.65-5
> 
>   # write random bits to p1
>   dd of=${dev}p1 if=/dev/urandom count=1
>   dd if=${dev}p1 of=p1-copy.pre count=1
>   parted -s $dev mkpart p4 37s 37s
>   blockdev --flushbufs $dev # FIXME: required with device-mapper-1.02.65-5
> 
>   dd if=${dev}p1 of=p1-copy.post count=1
>   cmp -l p1-copy.pre p1-copy.post
> 
> With that, the "cmp" show no differences.
> 
> Does this sound like a problem in device-mapper land,
> or in how parted interacts with DM?
> 
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