[Info-vax] Backup API mailbox oddity

[Stephen Hoffman]

On 2018-01-10 20:39:23 +0000, osuvman50 at gmail.com said:

> On Wednesday, January 10, 2018 at 1:06:14 PM UTC-5, Stephen Hoffman wrote:
>> On 2018-01-10 17:15:55 +0000, osuvman50 at gmail.com said:
>>> The easy workaround is to make the application WRITEOF before writing 
>>> the file list.
>>> 
>>> Also if you send BACKUP$START() no files, it gets confused and thinks 
>>> you are trying to list a save set.
>> 
>> I'd try $qio calls on the mailbox and quite possibly an AST-driven read 
>>  loop. or would maybe use a binary-mode fopen access request.   Or post 
>>  some code, and we'll have a look.
> 
> The reading part is in the bowels BACKUPSHR.EXE from being told the 
> mailbox logical name is the input file.  The writing to the mailbox is 
> an AST-driven write loop via direct $qio calls.

Ah, nevermind.    I remember this API.  It's a little different.   The 
call to BACKUP$START is synchronous.  It doesn't return until the 
operation is completed.

The following is one of the more remarkable bits of API documentation 
in the whole of the documentation set, too:

"Where possible, the Backup API emulates the behavior of the 
interactive BACKUP utility if you pass a call that contains conflicting 
qualifiers by:
	1	Making a best guess as to your intentions
	2	Ignoring the least likely of the conflicting qualifiers
	3	Issuing a message that warns of the conflicting qualifiers
	4	Processing the BACKUP request"


If it's getting confused and not the "we're going to guess what the 
caller meant" feature, log a bug with VSI.

For this case, post some code, and somebody here can have a look.


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