[Qemu-devel] [Bug 1185228] Re: with 'monitor pty', it needs to flush pts device after sending command to it

[Paolo Bonzini]

This is not a bug.  What happens is that QEMU echoes the command you
type onto the PTY. If you do not do a "cat /dev/pts/8", the PTY's buffer
gets full and QEMU stops reading from the PTY until it is emptied.

It doesn't happen if you use QMP.

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

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https://bugs.launchpad.net/bugs/1185228

Title:
  with 'monitor pty', it needs to flush pts device after sending command
  to it

Status in QEMU:
  Invalid

Bug description:
  Environment:
  ------------
  Host OS (ia32/ia32e/IA64):ia32e
  Guest OS (ia32/ia32e/IA64):ia32e
  Guest OS Type (Linux/Windows):Linux
  kvm.git Commit: 660696d1d16a71e15549ce1bf74953be1592bcd3
  qemu.git Commit: 64afc2b4d48fb21e085517c38a59a3f61a11283c
  Host Kernel Version:3.9.0-rc3
  Hardware: SandyBridge

  Bug detailed description:
  --------------------------
  when creating guest with parameter "-monitor pty", then send command (e.g. 
migrate, device_add) to the pts device.  If I don't flush the pts device (e.g. 
using cat /dev/pts/8) to flush the pts device, the monitor command doesn't take 
effect. I know some old qemu (e.g. 1.3) didn't have this issue.

  
  create KVM guest:
  address@hidden ~]# qemu-system-x86_64 -enable-kvm -m 1024 -smp 2  -net none 
/root/cathy/rhel6u4.qcow -monitor pty
  char device redirected to /dev/pts/8 (label compat_monitor0)
  VNC server running on `::1:5900'

  hot plug a PCI device:
  address@hidden ~]# echo "device_add pci-assign,host=05:10.0,id=nic" 
>/dev/pts/8
   (here, the device cannot hot plug to the guest.)

  if you run command "cat /dev/pts/8", the device will hot plug to the
  guest.

  hot remove the device:
  address@hidden ~]# echo "device_del nic">/dev/pts/8
  (here, the device cannot hot remove from the guest.)

  if you run command "cat /dev/pts/8" the device can hot remove from the
  guest


  Reproduce steps:
  ----------------
  1. qemu-system-x86_64 -enable-kvm -m 1024 -smp 2  -net none 
/root/cathy/rhel6u4.qcow -monitor pty
  2. echo "device_add pci-assign,host=05:10.0,id=nic" >/dev/pts/8
  (or using 'migrate' command in qemu monitor redirection device /dev/pts/8 )

  
  Current result:
  ----------------
  device can not hot plug or hot remove from the guest before exec 'cat 
/dev/pts/8'.

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