Re: [Qemu-devel] [PATCH 2/3] scsi-disk: Add device_id property

[Peter Krempa <pkrempa@redhat.com>]

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On Fri, Jan 25, 2019 at 18:46:52 +0100, Kevin Wolf wrote:
> The new device_id property specifies which value to use for the vendor
> specific designator in the Device Identification VPD page.
> 
> In particular, this is necessary for libvirt to maintain guest ABI
> compatibility when no serial number is given and a VM is switched from
> -drive (where the BlockBackend name is used) to -blockdev (where the
> vendor specific designator is left out by default).
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  hw/scsi/scsi-disk.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)

[...]

> @@ -2904,7 +2910,9 @@ static const TypeInfo scsi_disk_base_info = {
>      DEFINE_PROP_STRING("ver", SCSIDiskState, version),               \
>      DEFINE_PROP_STRING("serial", SCSIDiskState, serial),             \
>      DEFINE_PROP_STRING("vendor", SCSIDiskState, vendor),             \
> -    DEFINE_PROP_STRING("product", SCSIDiskState, product)
> +    DEFINE_PROP_STRING("product", SCSIDiskState, product),           \
> +    DEFINE_PROP_STRING("device_id", SCSIDiskState, device_id)

This adds the property only to 'scsi-disk', whereas libvirt will use
'scsi-cd' or 'scsi-hd' depending on the media type if the 'scsi-cd'
device is detected. The following logic decides:

https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/qemu/qemu_command.c;h=3e46f3ced3c1e6a4865e98e2d0cdce3214c4a5d2;hb=HEAD#l1978

This brings multiple questions:

1) Is this necssary also for scsi-cd/scsi-hd and if yes, the property
does not seem to be present for those

2) Is actually using 'scsi-cd'/'scsi-hd' the better option than
'scsi-disk'?

3) Since upstream libvirt supports qemu-1.5 and newer and 'scsi-cd' is
already supported there, can we assume that all newer versions support
it? (Basically the question is whether it can be compiled out by
upstream means).



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