[Info-vax] Migration Source Code Changes (was: Re: The VMS terminal driver...)

[Stephen Hoffman]

On 2018-12-13 04:24:16 +0000, Dave Froble said:

> On 12/12/2018 10:04 PM, Robert A. Brooks wrote:
>> New data structure -- I/O buffer descriptor (IOBD)
>> 
>> It'll be a requirement for X86, and will also work for IA64.
>> ...
> 
> Rob, you don't mention at what level this will be required.  Device 
> drivers?  Any I/O buffer?

What I've gathered from various discussions so far...

◆Most (and likely all) inner-mode code that directly references the 
memory page tables and the page table entries will have to change.  
(This involves some device drivers, some execlets and some UWSS code.  
Unsure about PFN-mapping user-mode code.)
◆By all accounts, the page table design is very different, and I'm 
inferring a whole lot of what amounts to double-mapping of memory pages 
is being implemented.
◆There's a memory page size change inbound, though the new page size 
value is exactly half the size of an existing memory page size and 
which means that most existing Alpha and I64 allocations and mappings 
will continue work.
◆Last I heard, VSI was undecided around presenting mixed memory page 
sizes and particularly the yet-larger page sizes.
◆There are IP-stack-related changes also inbound, around the migration 
away from the HPE TCP/IP Stack. That'll (mostly) hit TCP/IP-specific 
supporting procedures and related tools, and app testing, as the C and 
$qio APIs are intentionally compatible.
◆The 64-bit I/O sector size and addressing promotions, and those will 
(eventually) hit anything that knows about an LBN or a VBN or the 
related fields in the RMS and XQP data structures; that's the second 
part of VAFS support.  These addressing are presently optional for app 
developers, as existing apps will only need these changes when the app 
encounters VAFS use on storage devices past 2 TiB.
◆Migrating to the newer compilers and particularly those with newer 
standards support is presently optional, though some those migrations 
will likely require source changes with at least some of the 
programming languages.

More than a few other details and changes beyond these undoubtedly 
await.   Most user-mode code will be compile-and-go.

VSI is accruing details for their app migration documentation, more 
presentations will be available at future boot camps, etc.


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