Assuming I understand your question, i.e. "what does use_diag control?"
As Obi-Wan would say, "Use the Source, Luke!"

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c

<quote>

818 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L818>
*/**819 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L819>
* * use_diag controls whether the driver should use diag rather than
ssch*820 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L820>
* * to talk to the device*821
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L821>
* */*822 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L822>
static ssize_t 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=ssize_t>823
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L823>
dasd_use_diag_show
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dasd_use_diag_show>(struct
device <http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=device>
*dev <http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dev>,
struct device_attribute
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=device_attribute>
*attr <http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=attr>,
char *buf <http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=buf>)824
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L824>
{825 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L825>
        struct dasd_devmap
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dasd_devmap>
*devmap;826 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L826>
        int use_diag;827
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L827>
828 
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L828>
        devmap = dasd_find_busid
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dasd_find_busid>(dev_name
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dev_name>(dev
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=dev>));829
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L829>
        if (!IS_ERR
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=IS_ERR>(devmap))830
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L830>
                use_diag = (devmap->features
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=features> &
DASD_FEATURE_USEDIAG) != 0;831
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L831>
        else832
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L832>
                use_diag = (DASD_FEATURE_DEFAULT &
DASD_FEATURE_USEDIAG) != 0;833
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L833>
        return sprintf
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=sprintf>(buf
<http://www.cs.fsu.edu/~baker/devices/lxr/http/ident?i=buf>, use_diag
? *"1\n"* : *"\n"*);834
<http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/drivers/s390/block/dasd_devmap.c#L834>
}

</quote>

On Mon, Dec 31, 2012 at 11:18 AM, Bauer, Bobby (NIH/CIT) [E] <
[email protected]> wrote:

> Been reading, always a dangerous thing.
> In Chapter 25. Configuring an Installed Linux on System z Instance, I see
> in zipl.conf, USE_DIAG=0. In dasd.conf I see USE_DIAG=1. What is the
> difference? Where do I find these? I don't have a USE_DIAG coded in my
> zipl.conf.
>
> Goggling around I also found a hit that said using USE_DIAG=1 doesn't
> allow the allocation of a swap file.
>
> Bobby Bauer
> Center for Information Technology
> National Institutes of Health
> Bethesda, MD 20892-5628
> 301-594-7474
>



--
Maranatha! <><
John McKown

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