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Re: [Qemu-block] [Nbd] [PATCH] doc: Propose NBD_FLAG_INIT_ZEROES extensi
From: |
Alex Bligh |
Subject: |
Re: [Qemu-block] [Nbd] [PATCH] doc: Propose NBD_FLAG_INIT_ZEROES extension |
Date: |
Tue, 6 Dec 2016 08:46:43 +0000 |
> On 5 Dec 2016, at 23:42, Eric Blake <address@hidden> wrote:
>
> While not directly related to NBD_CMD_WRITE_ZEROES, the qemu
> team discovered that it is useful if a server can advertise
> whether an export is in a known-all-zeroes state at the time
> the client connects.
I think this is good to go, and ...
> Signed-off-by: Eric Blake <address@hidden>
> ---
> doc/proto.md | 5 +++++
> 1 file changed, 5 insertions(+)
>
> This replaces the following qemu patch attempt:
> https://lists.gnu.org/archive/html/qemu-devel/2016-12/msg00357.html
> which tried to add NBD_CMD_HAS_ZERO_INIT with poor semantics. The
> semantics in this proposal should be much better.
>
> Patch is to the merge of the master branch and the
> extension-write-zeroes branch. By the way, qemu 2.8 is due
> to be released "real soon now", and implements NBD_CMD_WRITE_ZEROES,
> so maybe it is time to consider promoting the extension-write-zeroes
> branch into master.
I would support this.
In fact the patch is sufficiently simple I think I'd merge this
into extension-write-zeroes then merge that into master.
Wouter?
Alex
> diff --git a/doc/proto.md b/doc/proto.md
> index afe71fc..7e4ec7f 100644
> --- a/doc/proto.md
> +++ b/doc/proto.md
> @@ -697,6 +697,11 @@ The field has the following format:
> the export.
> - bit 9, `NBD_FLAG_SEND_BLOCK_STATUS`: defined by the experimental
> `BLOCK_STATUS`
> [extension](https://github.com/NetworkBlockDevice/nbd/blob/extension-blockstatus/doc/proto.md).
> +- bit 10, `NBD_FLAG_INIT_ZEROES`: Indicates that the server guarantees
> + that at the time transmission phase begins, all offsets within the
> + export read as zero bytes. Clients MAY use this information to
> + avoid writing to sections of the export that should still read as
> + zero after the client is done writing.
>
> Clients SHOULD ignore unknown flags.
>
> --
> 2.9.3
>
>
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--
Alex Bligh
Re: [Qemu-block] [PATCH] doc: Propose NBD_FLAG_INIT_ZEROES extension, Stefan Hajnoczi, 2016/12/06
Re: [Qemu-block] [Nbd] [PATCH] doc: Propose NBD_FLAG_INIT_ZEROES extension, Wouter Verhelst, 2016/12/12