Paolo Bonzini <pbonz...@redhat.com> writes:
> Il 16/09/2014 09:21, Markus Armbruster ha scritto:
>> The rebase onto QOM renamed name to legacy_name, to free name for use as
>> QOM type name (commit cafe5bd).
>
> Also, the QOM type name has strict rules:
>
> - either it is a QAPI type (primitive, enum or struct)
>
> - or it is link<qom-type-name>
>
> - or it is child<qom-type-name>
>
> The qdev type names had no rules. We had uint8, hex8, on/off, drive, etc.
>
>> Human users do, however. I'd object to a degradation of -device
>> FOO,help. Changing it is fine, but it should remain at least as helpful
>> as it is now.
>
> The question is if it is really a degradation.
>
> Example 1:
>
> virtio-blk-pci.physical_block_size=blocksize
> virtio-blk-pci.logical_block_size=blocksize
>
> vs.
>
> virtio-blk-pci.physical_block_size=uint16
> virtio-blk-pci.logical_block_size=uint16
>
> What is a "blocksize"? It is a power of two between 512 and 32768, but
> how does the user know? If the value is too small or invalid, the
> error message is particularly helpful for QEMU standards:
>
> qemu-system-x86_64: -device
> virtio-blk-pci,physical_block_size=128,drive=hd:
> Property .physical_block_size doesn't take value 128 (minimum:
> 512, maximum:
> 32768)
>
> qemu-system-x86_64: -device
> virtio-blk-pci,physical_block_size=1023,drive=hd:
> Property .physical_block_size doesn't take value '1023', it's not
> a power of 2
>
> I think uint16 is actually more informative than "blocksize".
Neither is particularly user-friendly, but I grant you uint16 is less
bad than blocksize in absence of definitions for these terms.
> Example 2:
>
> virtio-blk-pci.drive=drive
>
> vs.
>
> virtio-blk-pci.drive=str
>
> The fact that it points to a -drive is already guessable (for anyone who
> knows the relationship between -drive and -device) from the name of the
> property.
>
> $ qemu-system-x86_64 -drive if=none,file=$HOME/test2.img,id=hd
> -device virtio-blk-pci
> qemu-system-x86_64: -device virtio-blk-pci: drive property not set
> qemu-system-x86_64: -device virtio-blk-pci: Device initialization failed.
> qemu-system-x86_64: -device virtio-blk-pci: Device
> virtio-blk-pci' could not be
> initialized
>
> $ qemu-system-x86_64 -drive if=none,file=$HOME/test2.img,id=hd
> -device virtio-blk-pci,drive=ff
> qemu-system-x86_64: -device virtio-blk-pci,drive=ff: Property
> 'virtio-blk-device.drive' can't find value 'ff'
>
> If we QOMified BlockBackend, BTW, it would show up as
>
> virtio-blk-pci.drive=link<block-backend>
>
> I think both "str" and "link<block-backend>" actually are a small degradation
> compared to "drive", and this is why I kept the legacy_name. But overall I
> think it's not really worth the layering violation that patches 2 and 3 are;
> and it's definitely not stable material.
"str" is clearly a degradation for me. I breaks usage like
for i in `qemu -device help 2>&1 | sed -n 's/^name "\([^"]*\)".*/\1/p'`
do qemu -device $i,help 2>&1
done | grep =drive
Finds all block device models. I've done such things many times.
Whether "link<block-backend>" is a degradation or an improvement is
debatable.
> I'd rather drop the legacy_name at all. Here are the legacy_names currently
> in use:
>
> hw/core/qdev-properties-system.c: .legacy_name = "drive",
> hw/core/qdev-properties-system.c: .legacy_name = "chr",
> hw/core/qdev-properties-system.c: .legacy_name = "netdev",
> hw/core/qdev-properties-system.c: .legacy_name = "vlan",
> hw/core/qdev-properties.c: .legacy_name = "on/off",
> hw/core/qdev-properties.c: .legacy_name = "macaddr",
> hw/core/qdev-properties.c: .legacy_name = "bios-chs-trans",
> hw/core/qdev-properties.c: .legacy_name = "pci-devfn",
> hw/core/qdev-properties.c: .legacy_name = "blocksize",
> hw/core/qdev-properties.c: .legacy_name = "pci-host-devaddr",
You missed
target-ppc/translate_init.c:8047: .legacy_name = "powerpc-server-compat",
which is another enum. Aside: it should really use the infrastructure
for enums.
>
> vlan is just a glorified int, not an id like the others. chr should be
> named chardev. blocksize, I already covered above. bios-chs-trans is
> an enum (QAPI name BiosAtaTranslation) and is useless. on/off vs.
> bool is just bikeshedding. macaddr is obviously a string, whose format
> is clear from the property name.
>
> pci-host-devaddr and pci-devfn are the only ones that do not have an
> obvious property name (respectively "host" and "addr").
Agree on the uselessness of "on/off".
Agree on the uselessness of "blocksize" without a definition of the
term.
"chr" and "netdev" are like "drive", and replacing them by "str" is a
degradation in my book.
Help for enum-valued properties in the form of "prop=ENUM-NAME" is not
really helpful without a definition of ENUM-NAME. It's still useful for
finding devices with this kind of property.
Same for structured strings like macaddr, pci-devfn, pci-host-devaddr.
legacy_name provides lousy help. But it's better than nothing, and I'd
hate to see it dropped without a suitable replacement.
