[Info-vax] QIO Writes to a mailbox

[JF Mezei]

Johnny Billquist wrote:

> No. This is not correct. QIO, as well as QIOW will not copy the data 
> before returning from the system call. 

QIOW by definition waits for an event flag to be set to signal that the
IO has completed, so this garantees that the buffer has not only been
copied, but also been written in full to the mailbox device.

I've always used QIOW to write to mailbox devices. (but QIO to read from
them with AST routines etc).

But when QIO executes, doesn't it invoke some driver code to "queue" the
IO, and isn't it possible that for a write to memory device, that drive
code might actually do the write to the mailbox device ?

And if a mailbox is full, I know that QIOW will cause process to hang on
a RWMBX, but would a QIO also result in this ?