Re: [PATCH 0/2] Introduce printer subsystem and USB printer device

[Gerd Hoffmann]

  Hi,

> This patchset introduces:
> 
> 1) Skeleton of QEMU printer subsystem with a dummy builtin driver.
> 
> 2) USB printer device emulation, with definitions in the extension of 
> IPP-over-
>    USB [3].
> 
> WIP:
> 
> 1) QEMU printer subsystem interfaces, which will be finalized with a concrete
>    backend driver.
> 
> 2) IPP-over-USB implementation.

Hmm, I'm wondering what uses cases you have in mind and whenever
it makes sense to introduce a printer subsystem?

Having an ipp-over-usb device looks useful, but the only use case I can
see is to allow guests access a network printer.  I can't see the
benefits of a printer subsystem, especially in a world where non-ipp
printers are going extinct.  We would most likely have just a single
kind of printer backend, where the only job qemu will have is to
forwarding requests and replies, maybe with some http header rewriting.

Likewise usb would be the one and only device (parallel ports are long
gone in printers).  So the indirection added by a printer subsystem
doesn't buy us anything because we just don't need that flexibility.
I'd suggest to pass the url directly to the device instead:

qemu -device usb-ipp-printer,url=ipp://hostname/ipp/printer

take care,
  Gerd