[Bug 1381846] Re: Data sent to parallel port in guest is lost if host buffer fills up

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to another 
system. For this we need to know which bugs are still valid and which could be 
closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state 
back to "New" within the next 60 days, otherwise this report will be marked as 
"Expired". Or mark it as "Fix Released" if the problem has been solved with a 
newer version of QEMU already. Thank you and sorry for the inconvenience.

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1381846

Title:
  Data sent to parallel port in guest is lost if host buffer fills up

Status in QEMU:
  Incomplete

Bug description:
  It appears that qemu will blindly write characters out to the chardev
  and drop them on the floor if a write fails with EAGAIN, without
  initiating flow control (via BUSY and ACK) back to the guest. If the
  host buffer is too small, or is talking to a hardware device that is
  too slow, data will be lost.

  I notice this problem when I run a DOS program with this on the qemu command 
line:
  -parallel /dev/usb/lp0

  I can work around this problem by buffering via a pipe, but this looks
  like a general problem. Is there a way to wire up the readiness of the
  output chardev to the parallel port ACK and BUSY lines, and signal an
  ISA interrupt? I don't know the code well enough to tell.

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