Re: equivalent to "-drive if=ide,id=disk0....."

[Kashyap Chamarthy]

On Tue, Jul 28, 2020 at 01:06:48PM +0200, Kevin Wolf wrote:
> Am 27.07.2020 um 23:50 hat Kashyap Chamarthy geschrieben:

[...]

> > IIUC, specifying 'node-name' should be sufficient.  Also, you don't need
> > to specify JSON syntax on the command-line; you can 'flatten it' (see
> > below).
> 
> Indeed, naming BlockBackends is a legacy thing. You should never need
> it. Guest devices can be created like -device ide-hd,drive=<node-name>
> and QMP commands either accept node names (if they are about the
> backend) or the ID of the guest device (if they are about the frontend).

Thanks for the explanation.

> > On 'id' vs. 'node-name', from the documentation of `blockdev-add`,
> > https://git.qemu.org/gitweb.cgi?p=qemu.git;a=blob;f=qapi/block-core.json#l4032
> > 
> >     # Creates a new block device. If the @id option is given at the top 
> > level, a
> >     # BlockBackend will be created; otherwise, @node-name is mandatory at 
> > the top
> >     # level and no BlockBackend will be created.
> 
> This is actually a documentation bug. @id doesn't exist, blockdev-add
> never creates a BlockBackend. This was different in the very first
> versions of the patches to add blockdev-add and we probably just forgot
> to update the documentation after removing it.

Ah, noted; sent this one (per this thread and #qemu, OFTC, IRC discussion):

    https://lists.nongnu.org/archive/html/qemu-devel/2020-07/msg07929.html
    – qapi/block-core.json: Remove stale description of 'blockdev-add'

> > And here's a minimal working example that I use with '-blockdev'
> > 
> > /usr/bin/qemu-system-x86_64        \
> >     -display none                  \
> >     -no-user-config                \
> >     -nodefaults                    \
> >     -serial  stdio                 \
> >     -cpu host                      \
> >     -smp 1,maxcpus=2               \
> >     -machine q35,accel=kvm,usb=off \
> >     -m 2048                        \
> >     -blockdev 
> > node-name=node-Base,driver=qcow2,file.driver=file,file.filename=./base.qcow2
> >  \
> >     -device virtio-blk,drive=node-Base,id=virtio0 \
> 
> Yes, this works. Another option is to define each block node separately:
> 
>     ...
>     -blockdev node-name=base-file,driver=file,filename=base.qcow2 \
>     -blockdev node-name=base,driver=qcow2,file=base-file \
>     ...

That is more readable too; thanks.


> Kevin

-- 
/kashyap