Re: [Xen-devel] [RFC PATCH] blkif.h: document scsi/0x12/0x83 node

[Bob Liu <bob.liu@xxxxxxxxxx>]

On 03/17/2016 07:12 PM, Ian Jackson wrote:
> David Vrabel writes ("Re: [Xen-devel] [RFC PATCH] blkif.h: document 
> scsi/0x12/0x83 node"):
>> On 16/03/16 13:59, Bob Liu wrote:
>>> But we'd like to get the VPD information(of underlying storage device) also 
>>> in Linux blkfront, even blkfront is not a SCSI device.
>>
>> Why does blkback/blkfront need to involved here?  This is just some
>> xenstore keys that can be written by the toolstack and directly read by
>> the relevant application in the guest.
> 

They want a more generic way because the application may run on all kinds of 
environment including baremetal.
So they prefers to just call ioctl(SG_IO) against a storage device.

> I'm getting rather a different picture here than at first.  Previously
> I thought you had some 3rd-party application, not under your control,
> which expected to see this VPD data.
> 
> But now I think that you're saying the application is under your own
> control.  I don't understand why synthetic VPD data is the best way to
> give your application the information it needs.
> 
> What is the application doing with this VPD data ?  I mean,
> which specific application functions, and how do they depend on the
> VPD data ?
> 

From the feedbacks I just got, they do *not* want the details to be in public.

Anyway, I think this is not a block of this patch.
In Windows PV block driver, we already use the same way to get the raw INQUIRY 
data.
 * The Windows PV block driver accepts ioctl(SG_IO).
 * Then it reads this /scsi/0x12/0x83 node.
 * Then return the raw INQURIY data back to ioctl.

Since Linux guest also wants to do the same thing, let's making this mechanism 
to be a generic interface!
I'll post a patch adding ioctl(SG_IO) support to xen-blkfront together with a 
updated version of this patch soon.

Thanks,
Bob

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