>>> On 10/17/2016 at 02:23 AM, Paul Schuster <pgs4ibmm...@pacbell.net> wrote: 
> I am issuing DIAGNOSE 8 on my z/os image under VM (z/vm) to do a QUERY 
> VIRTUAL DASD.  It works*up to a certain point:
> The QUERY VIRTUAL DASD command returns (for me) 38617 (decimal) bytes, 
> according to the CC=0 after the DIAGNOSE 8 command.  My buffer is large 
> enough to accommodate this.  I have tried several different sub-pools of 
> storage.  I PGSER FIX the buffer pages.  I do a SYSEVENT DONTSWAP.  I do a 
> LRA of the virtual address of the start of the buffer.  The DIAGNOSE 
> completes CC=0. But, in my buffer, I am only seeing the first page (4095) 
> bytes of the output.  
> My question: I don*t see any documented restriction in the VM manuals that 
> limits the DIAGNOSE 8 output buffer to 4K (rather the limitation is the 
> architecture limit depending on your amode.) The z/vm manuals say the buffer 
> can cross page boundaries.  So is there a way to force the real storage 
> addresses of the page-fixed pages to be consecutive?  According to the 
> diagnose 8 doc., the buffer needs to be in guest-real storage, hence the LRA. 
>  And it is working for the first 4k page.
> Thank you for any insight you can provide.

I have no idea how well the concepts will transfer, but Linux has had a command 
that issues DIAGNOSE 8 calls for a very long time now.  That command was 
originally "hcp" by Neale Ferguson, but then IBM created a different version 
called "vmcp".  Those commands work, so you might be able to figure out what 
they're doing and apply that to your program.

Mark Post

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