Re: [Qemu-devel] [RFC 10/15] s390-bios: Support for running format-0/1 channel programs

[Cornelia Huck]

On Fri, 6 Jul 2018 10:35:06 -0400
"Jason J. Herne" <address@hidden> wrote:

> On 07/06/2018 04:03 AM, Cornelia Huck wrote:
> > On Thu,  5 Jul 2018 13:25:38 -0400
> > "Jason J. Herne" <address@hidden> wrote:

> >> +    senseIdCcw.count = sizeof(senseData);
> >> +
> >> +    if (do_cio(schid, ptr2u32(&senseIdCcw), CCW_FMT1)) {
> >> +        panic("Failed to run SenseID CCw\n");
> >> +    }
> >> +
> >> +    return senseData.cu_type;
> >> +}
> >> +
> >> +static bool irb_error(Irb *irb)
> >> +{
> >> +    /* We have to ignore Incorrect Length (cstat == 0x40) indicators 
> >> because
> >> +     * real devices expect a 24 byte SenseID  buffer, and virtio devices 
> >> expect
> >> +     * a much larger buffer. Neither device type can tolerate a buffer 
> >> size
> >> +     * different from what they expect so they set this indicator.  
> > 
> > Hm... do you have details? Is that basic vs. extended SenseID
> > information?
> > 
> > (If the code in QEMU is making incorrect assumptions, I'd like to fix
> > that.)  
> 
> I really have no idea and was hoping someone who knows virtio ccw better 
> than myself would have some ideas. This comment simply documents what I 
> discovered in testing. I can look into it more if no one else has any 
> information on this. FWIW, it has been working without issue in my testing.

OK, I've looked at this a bit more. It seems that we always get at
least the basic information; the command, however, provides for a
variable length (the CIWs).

The Linux kernel always tries to get the maximum length (basic sense id
information + maximum number possible number of CIWs), but sets SLI as
it may get less of that. I'm not sure what I should return in QEMU for
emulated devices, the documentation of SenseID I could find is a bit
light on details (as the data can be of variable length). I think you
should simply always use SLI, as you don't know the length of the
SenseID data you can get beforehand.

(BTW, is there a newer public version of SA22-7204-01 - Common I/O
Device Commands - available? That one is a bit dated.)