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Re: [Qemu-block] [Qemu-devel] [PATCH RFC 7/7] nbd/replication: implement

From: Hailiang Zhang
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH RFC 7/7] nbd/replication: implement .bdrv_get_info() for nbd and replication driver
Date: Mon, 24 Oct 2016 10:44:23 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1


On 2016/10/20 23:34, Eric Blake wrote:
On 10/20/2016 08:57 AM, zhanghailiang wrote:
Without this callback, there will be an error reports in the primary side:
"qemu-system-x86_64: Couldn't determine the cluster size of the target image,
which has no backing file: Operation not supported
Aborting, since this may create an unusable destination image"

For nbd driver, it doesn't have cluster size, so here we return
a fake value for it.

Signed-off-by: zhanghailiang <address@hidden>
Signed-off-by: Wen Congyang <address@hidden>
  block/nbd.c         | 12 ++++++++++++
  block/replication.c |  6 ++++++
  2 files changed, 18 insertions(+)

diff --git a/block/nbd.c b/block/nbd.c
index 6bc06d6..96d7023 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -40,6 +40,8 @@

  #define EN_OPTSTR ":exportname="


Why 512?  NBD allows byte-addressable operations (even if it is more
efficient on aligned I/O); and I've been working hard to convert things
to the point that NBD does not enforce alignment on other layers.
Wouldn't 1 be better?

Yes, that makes no difference for block replication driver. :)

+static int nbd_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
+    bdi->cluster_size  = NBD_FAKE_CLUSTER_SIZE;

I also have patches written (but waiting for NBD write zeroes support to
be reviewed first) that add support for the experimental NBD block info,
that lets a server advertise actual sizes to the client rather than
having to guess.  Here's the last time I posted a preview of it:


It would be nice to use that instead of just faking things.

That's great, that's what we really want, here it is just a
temporary solution, I'll drop this patch after you nbd patch been merged.


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