Re: [Qemu-devel] [PATCH v2 03/15] qdev: Allow device addressing via 'driver.instance'

[Markus Armbruster]

Jan Kiszka <address@hidden> writes:

> From: Jan Kiszka <address@hidden>
>
> Extend qbus_find_dev to allow addressing of devices without an unique id
> via an optional per-bus instance number. The new formats are
> 'driver.instance' and 'alias.instance'.
>
> Signed-off-by: Jan Kiszka <address@hidden>
> ---
>  docs/qdev-device-use.txt |   12 +++++++++++-
>  hw/qdev.c                |   23 ++++++++++++++++++-----
>  2 files changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/docs/qdev-device-use.txt b/docs/qdev-device-use.txt
> index 9ac1fa1..5939481 100644
> --- a/docs/qdev-device-use.txt
> +++ b/docs/qdev-device-use.txt
> @@ -1,6 +1,6 @@
>  = How to convert to -device & friends =
>  
> -=== Specifying Bus and Address on Bus ===
> +=== Specifying Bus, Address on Bus, and Devices ===
>  
>  In qdev, each device has a parent bus.  Some devices provide one or
>  more buses for children.  You can specify a device's parent bus with
> @@ -24,6 +24,16 @@ Furthermore, if a device only hosts a single bus, the bus 
> name can be
>  omitted in the path.  Example: /i440FX-pcihost/PIIX3 abbreviates
>  /i440FX-pcihost/pci.0/PIIX3/isa.0 as none of the buses has siblings.
>  
> +Existing devices can be addressed either via a unique ID if it was
> +assigned during creation or via the device tree path:
> +
> +/full_bus_address/driver_name[.instance_number]
> +    or
> +abbreviated_bus_address/driver_name[.instance_number]
> +
> +Example: /i440FX-pcihost/pci.0/e1000.2 addresses the second e1000
> +adapter on the bus 'pci.0'.
> +
>  Note: the USB device address can't be controlled at this time.

"instance number" isn't defined in this document.

I understand the problem you're trying to solve; I've had it myself many
times.  But is inventing an instance number the right solution?

The two e1000 devices already have a perfectly fine unique identifier on
their bus: their bus address.  What about recognizing bus addresses in
paths?  Requires a suitable restriction on device names and IDs to avoid
ambiguity, say "start with letter".

qdev currently doesn't abstract bus addresses, but that's fixable.

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