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Re: [Qemu-devel] [PATCH] doc: Allow NBD_CMD_FLAG_NO_HOLE during NBD_CMD_

From: Denis V. Lunev
Subject: Re: [Qemu-devel] [PATCH] doc: Allow NBD_CMD_FLAG_NO_HOLE during NBD_CMD_WRITE
Date: Mon, 4 Apr 2016 17:47:41 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

On 04/04/2016 05:15 PM, Eric Blake wrote:
qemu already has an existing server implementation option that will
explicitly search the payload of NBD_CMD_WRITE for large blocks of
zeroes, and punch holes in the underlying file.  For old clients
that don't know how to use the new NBD_CMD_WRITE_ZEROES, this is a
workaround to keep the server's destination file approximately as
sparse as the client's source.  However, for new clients that know
how to explicitly request holes, it is unnecessary overhead; and
can lead to the server punching a hole and risking fragmentation or
future ENOSPC even when the client explicitly wanted to write
zeroes rather than a hole.  So it makes sense to let the new

Signed-off-by: Eric Blake <address@hidden>

what behaviour do you expect  for QCOW2 file?
We should fully provision that image as far as I could understand,
i.e. allocate data blocks with zero content.

I think that this would work.

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