Re: [Qemu-devel] [PATCH 1/2] hmp: 'drive_add -n' for creating a node without BB

[Kevin Wolf <kwolf@redhat.com>]

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Am 24.02.2016 um 18:50 hat Max Reitz geschrieben:
> On 23.02.2016 18:16, Kevin Wolf wrote:
> > This patch adds an option to the drive_add HMP command to create only a
> > BlockDriverState without a BlockBackend on top.
> > 
> > The motivation for this is that libvirt needs to specify options to a
> > migration target (specifically, detect-zeroes). drive-mirror doesn't
> > allow specifying options, and the proper way to do this is to create the
> > target BDS separately with blockdev-add (where you can specify options)
> > and then use blockdev-mirror to that BDS.
> > 
> > However, libvirt can't use blockdev-add as long as it is still
> > experimental, and we're expecting that it will still take some time, so
> > we need to resort to drive_add.
> > 
> > The problem with drive_add is that so far it always created a BB, and
> > BDSes with a BB can't be used as a mirroring target as long as we don't
> > support multiple BBs per BDS - and while we're working towards that
> > goal, it's another thing that will still take some time.
> > 
> > So to achieve the goal, the simplest solution to provide the
> > functionality now without adding one-off options to the mirror QMP
> > commands is to extend drive_add to create nodes without BBs.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  blockdev.c                | 30 ++++++++++++++++++++++++++++++
> >  device-hotplug.c          |  7 +++++++
> >  hmp-commands.hx           |  4 ++--
> >  include/block/block_int.h |  2 ++
> >  4 files changed, 41 insertions(+), 2 deletions(-)
> > 
> 
> Patch looks good to me (well, except for it being a pity we have to fall
> back on this HMP command), I only have a minor suggestion:
> 
> [...]
> 
> > diff --git a/hmp-commands.hx b/hmp-commands.hx
> > index bb52e4d..3b44e52 100644
> > --- a/hmp-commands.hx
> > +++ b/hmp-commands.hx
> > @@ -1200,8 +1200,8 @@ ETEXI
> >  
> >      {
> >          .name       = "drive_add",
> > -        .args_type  = "pci_addr:s,opts:s",
> > -        .params     = "[[<domain>:]<bus>:]<slot>\n"
> > +        .args_type  = "node:-n,pci_addr:s,opts:s",
> > +        .params     = "[-n] [[<domain>:]<bus>:]<slot>\n"
> >                        "[file=file][,if=type][,bus=n]\n"
> >                        "[,unit=m][,media=d][,index=i]\n"
> >                        "[,cyls=c,heads=h,secs=s[,trans=t]]\n"
> 
> The description reads:
> 
> > Add drive to PCI storage controller.
> 
> Maybe this should be extended now?

It was already wrong before this patch, but I guess I could just add
another patch to the series anyway.

Kevin

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