netdev - Re: [PATCH 0/3] virtio-net: inline header support

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Date:	Fri, 05 Oct 2012 15:13:01 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Thomas Lendacky <tahm@...ux.vnet.ibm.com>, kvm@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, avi@...hat.com,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [PATCH 0/3] virtio-net: inline header support

Paolo Bonzini <pbonzini@...hat.com> writes:

> Il 04/10/2012 14:51, Rusty Russell ha scritto:
>> Paolo Bonzini <pbonzini@...hat.com> writes:
>> 
>>> Il 04/10/2012 02:11, Rusty Russell ha scritto:
>>>>>> There's a reason I haven't done this.  I really, really dislike "my
>>>>>> implemention isn't broken" feature bits.  We could have an infinite
>>>>>> number of them, for each bug in each device.
>>>>>
>>>>> However, this bug affects (almost) all implementations and (almost) all
>>>>> devices.  It even makes sense to reserve a transport feature bit for it
>>>>> instead of a device feature bit.
>>>>
>>>> Perhaps, but we have to fix the bugs first!
>>>
>>> Yes. :)  Isn't that what mst's patch does?
>>>
>>>> As I said, my torture patch broke qemu immediately.  Since noone has
>>>> leapt onto fixing that, I'll take a look now...
>>>
>>> I can look at virtio-scsi.
>> 
>> Actually, you can't, see my reply to Anthony...
>> 
>> Message-ID: <87lifm1y1n.fsf@...tcorp.com.au>
>
>     struct virtio_scsi_req_cmd {
>         // Read-only
>         u8 lun[8];
>         u64 id;
>         u8 task_attr;
>         u8 prio;
>         u8 crn;
>         char cdb[cdb_size];
>         char dataout[];
>         // Write-only part
>         u32 sense_len;
>         u32 residual;
>         u16 status_qualifier;
>         u8 status;
>         u8 response;
>         u8 sense[sense_size];
>         char datain[];
>     };
>
> where cdb_size and sense_size come from configuration space.  The device
> right now expects everything before dataout/datain to be in a single
> descriptor, but that's in no way part of the spec.  Am I missing
> something egregious?

Since you wrote it, I hope not :)

That's good.  But virtio_blk's scsi command is insoluble AFAICT.  As I
said to Anthony, the best rules are "always" and "never", so I'd really
rather not have to grandfather that in.

Cheers,
Rusty.
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