[TUHS] UNIX on S/370

Larry McVoy lm at mcvoy.com
Tue Nov 21 15:20:23 AEST 2017


On Mon, Nov 20, 2017 at 10:14:41PM -0700, Warner Losh wrote:
> I assume you aren't talking about things like mmap where you can't really
> bcopy it...

Correct.

> At Fusion I/O we had hooks into our PCIe flash card driver that would do
> DMA directly into user buffers (since we wanted IOPS and any extra copies
> got in the way of that). 

Yeah, cool, sorta like the SGI stuff, but that was stuff that you had to 
add and SGI had to add.

The only place I can see dma right into user buffers would be if the user
blocked in the read, it was to a raw device, *and* the OS took care to make
sure that those page[s] were locked.  I can see the 1st 2 but I've not run
into the last one except for specialized stuff like O_DIRECT.


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