Re: [Qemu-devel] [PATCH v2 5/7] qmp: add set-bootindex command

[Gonglei (Arei)]

Hi, Markus

> >> >> Subject: Re: [Qemu-devel] [PATCH v2 5/7] qmp: add set-bootindex
> command
> >> >>
> >> >> On Fri, Jul 25, 2014 at 02:52:50PM +0800, address@hidden
> wrote:
> >> >> > From: Gonglei <address@hidden>
> >> >> >
> >> >> > Adds "set-bootindex id=xx,bootindex=xx,suffix=xx" QMP command.
> >> >> >
> >> >> > Example QMP command:
> >> >> > -> { "execute": "set-bootindex", "arguments": { "id": "ide0-0-1",
> >> >> > "bootindex":
> >> >> 1, "suffix": "/address@hidden"}}
> >> >> > <- { "return": {} }
> >> >> >
> >> >> > Signed-off-by: Gonglei <address@hidden>
> >> >> > Signed-off-by: Chenliang <address@hidden>
> >> >> > ---
> >> >> >  qapi-schema.json | 16 ++++++++++++++++
> >> >> >  qmp-commands.hx  | 24 ++++++++++++++++++++++++
> >> >> >  qmp.c            | 17 +++++++++++++++++
> >> >> >  3 files changed, 57 insertions(+)
> >> >> >
> >> >> > diff --git a/qapi-schema.json b/qapi-schema.json
> >> >> > index b11aad2..a9ef0be 100644
> >> >> > --- a/qapi-schema.json
> >> >> > +++ b/qapi-schema.json
> >> >> > @@ -1704,6 +1704,22 @@
> >> >> >  { 'command': 'device_del', 'data': {'id': 'str'} }
> >> >> >
> >> >> >  ##
> >> >> > +# @set-bootindex:
> >> >> > +#
> >> >> > +# set bootindex of a devcie
> >> >> > +#
> >> >> > +# @id: the name of the device
> >> >> > +# @bootindex: the bootindex of the device
> >> >> > +# @suffix: #optional a suffix of the device
> >> >> > +#
> >> >> > +# Returns: Nothing on success
> >> >> > +#          If @id is not a valid device, DeviceNotFound
> >> >> > +#
> >> >> > +# Since: 2.2
> >> >> > +##
> >> >> > +{ 'command': 'set-bootindex', 'data': {'id': 'str', 'bootindex':
> >> >> > int', '*suffix':
> >> >> 'str'} }
> >> >> > +
> >> >> > +##
> >> >>
> >> >> I wonder if we could simply use qom-set for that. How many devices
> >> >> actually support having multiple bootindex entries with different
> >> >> suffixes?
> >> >>
> >> > AFAICT, the floppy device support two bootindex with different suffixes.
> >>
> >> Block device models commonly a single block device.  By convention,
> >> property "drive" is the backend, and property "bootindex" the bootindex,
> >> if the device model supports that.
> >>
> >> The device ID suffices to identify a block device for such device
> >> models.
> >>
> >> The floppy device model is an exception.  It folds multiple real-world
> >> objects into one: the controller and the actual drives.  Have a look at
> >> -device isa-fdc,help:
> >>
> >>     isa-fdc.iobase=uint32
> >>     isa-fdc.irq=uint32
> >>     isa-fdc.dma=uint32
> >>     isa-fdc.driveA=drive
> >>     isa-fdc.driveB=drive
> >>     isa-fdc.bootindexA=int32
> >>     isa-fdc.bootindexB=int32
> >>     isa-fdc.check_media_rate=on/off
> >>
> >> The properties ending with 'A' or 'B' apply to the first and the second
> >> drive, the others to the controller.
> >>
> >> Unfortunately, this means the device ID by itself doesn't identify the
> >> floppy device.
> >>
> > Yes.
> >
> >> Arguably, this is lousy modeling --- we really should model separate
> >> real-world objects as separate objects.  But making floppies pretty (or
> >> even sane) isn't anyone's priority nowadays.
> >>
> > Hmm... Agreed.
> >
> >> Since qom-set works on *properties*, I can't see why it couldn't be used
> >> for changing bootindexes.  There is no ambiguity even with floppy.
> >
> > Sorry?
> >
> >> You either set bootindexA or bootindexB.  No need to fuzz around with
> >> suffixes.  Or am I missing something?
> >
> > Your mean that we just need to think about change one bootindex? Either
> > set bootindexA or bootindexB, do not need pass suffix for identifying?
> 
> Eduardo suggested to think about using qom-set to update the bootindex.
> 
> Could look like
> 
>     { "execute": "qom-set",
>       "arguments": { "path": "/machine/unattached/device[15]",
>                      "property": "bootindexA", "value": 1 } }
> 
> Demonstrates an existing, well-defined way to identify the bootindex to
> change.  Do we really want to invent another one, based on suffix?
> 
> The value of "path" is the QOM path.  I can't remember offhand how to go
> from qdev ID to QOM path.  Onboard devices like isa-fdc don't have one
> anyway.
> 
> I also don't remember whether there's a nicer QOM path than this one.

Thanks for your explaining. TBH I haven't used "qom-set" before, so I
don't know what your mean (like Eduardo, sorry again). 

But now, I have a look at the implement of "qom-set" command, and 
I find the command is just change a device's property value, do not have
any other logic. For my case, we really change value of the global 
fw_boot_order list, 
which the device's bootindex property worked for actually. Only in this way,
we can attach our original target.

Best regards,
-Gonglei