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

[Markus Armbruster]

"Gonglei (Arei)" <address@hidden> writes:

> Hi,
>
>> 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.

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.

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.
You either set bootindexA or bootindexB.  No need to fuzz around with
suffixes.  Or am I missing something?