Re: [Qemu-devel] [Bug 1224444] [NEW] virtio-serial loses writes when used over virtio-mmio

["Laszlo Ersek \(Red Hat\)" <lersek@redhat.com>]

On 09/12/13 14:04, Richard Jones wrote:

> +     -chardev
socket,path=/home/rjones/d/libguestfs/tmp/libguestfsLa9dE2/guestfsd.sock,id=channel0
\

Is this a socket that libguestfs pre-creates on the host-side?

> the socket is never added to any poll/ppoll syscall, so it's no
> wonder that qemu never sees any data on the socket


This should be happening:

qemu_chr_open_socket() [qemu-char.c]
  unix_connect_opts() [util/qemu-sockets.c]
    qemu_socket()
    connect()
  qemu_set_nonblock() [util/oslib-posix.c]
  qemu_chr_open_socket_fd()
    socket_set_nodelay() [util/osdep.c]
    io_channel_from_socket()
      g_io_channel_unix_new()
    tcp_chr_connect()
      io_add_watch_poll()
        g_source_new()
        g_source_attach()
        g_source_unref()
      qemu_chr_be_generic_open()

io_add_watch_poll() should make sure the fd is polled starting with the
next main loop iteration.

Interestingly, even in the "successful" case, there's a slew of ppoll()
calls between connect() returning 6, and the first ppoll() that actually
covers fd=6.

Laszlo

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https://bugs.launchpad.net/bugs/1224444

Title:
  virtio-serial loses writes when used over virtio-mmio

Status in QEMU:
  New

Bug description:
  virtio-serial appears to lose writes, but only when used on top of
  virtio-mmio.  The scenario is this:

  /home/rjones/d/qemu/arm-softmmu/qemu-system-arm \
      -global virtio-blk-device.scsi=off \
      -nodefconfig \
      -nodefaults \
      -nographic \
      -M vexpress-a15 \
      -machine accel=kvm:tcg \
      -m 500 \
      -no-reboot \
      -kernel /home/rjones/d/libguestfs/tmp/.guestfs-1001/kernel.27944 \
      -dtb /home/rjones/d/libguestfs/tmp/.guestfs-1001/dtb.27944 \
      -initrd /home/rjones/d/libguestfs/tmp/.guestfs-1001/initrd.27944 \
      -device virtio-scsi-device,id=scsi \
      -drive file=/home/rjones/d/libguestfs/tmp/libguestfsLa9dE2/scratch.1,cache=unsafe,format=raw,id=hd0,if=none \
      -device scsi-hd,drive=hd0 \
      -drive file=/home/rjones/d/libguestfs/tmp/.guestfs-1001/root.27944,snapshot=on,id=appliance,cache=unsafe,if=none \
      -device scsi-hd,drive=appliance \
      -device virtio-serial-device \
      -serial stdio \
      -chardev socket,path=/home/rjones/d/libguestfs/tmp/libguestfsLa9dE2/guestfsd.sock,id=channel0 \
      -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 \
      -append 'panic=1 mem=500M console=ttyAMA0 udevtimeout=600 no_timer_check acpi=off printk.time=1 cgroup_disable=memory root=/dev/sdb selinux=0 guestfs_verbose=1 TERM=xterm-256color'

  After the guest starts up, a daemon writes 4 bytes to a virtio-serial
  socket.  The host side reads these 4 bytes correctly and writes a 64
  byte message.  The guest never sees this message.

  I enabled virtio-mmio debugging, and this is what is printed (## = my
  comment):

  ## guest opens the socket:
  trying to open virtio-serial channel '/dev/virtio-ports/org.libguestfs.channel.0'
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x3
  opened the socket, sock = 3
  udevadm settle
  ## guest writes 4 bytes to the socket:
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x5
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  sent magic GUESTFS_LAUNCH_FLAG
  ## host reads 4 bytes successfully:
  main_loop libguestfs: recv_from_daemon: received GUESTFS_LAUNCH_FLAG
  libguestfs: [14605ms] appliance is up
  Guest launched OK.
  ## host writes 64 bytes to socket:
  libguestfs: writing the data to the socket (size = 64)
  waiting for next request
  libguestfs: data written OK
  ## hangs here forever with guest in read() call never receiving any data

  I am using qemu from git today (2d1fe1873a984).

  Some notes:

  - It's not 100% reproducible.  Sometimes everything works fine, although it fails "often" (eg > 2/3rds of the time).
  - KVM is being used.
  - We've long used virtio-serial on x86 and have never seen anything like this.

  This is what the output looks like when it doesn't fail:

  trying to open virtio-serial channel '/dev/virtio-ports/org.libguestfs.channel.0
  '
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x3
  opened the socket, sock = 3
  udevadm settle
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x5
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  sent magic GUESTlibguestfs: recv_from_daemon: received GUESTFS_LAUNCH_FLAG
  libguestfs: [14710ms] appliance is up
  Guest launched OK.
  libguestfs: writing the data to the socket (size = 64)
  FS_LAUNCH_FLAG
  main_loop waiting for next request
  libguestfs: data written OK
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x2
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x2
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x0
  virtio_mmio: virtio_mmio setting IRQ 0
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  [... more virtio-mmio lines omitted ...]
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x0
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  guestfsd: main_loop: new request, len 0x3c
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x4
  0000: 20 00 f5 f5 00 00 00 04 00 00 00 d2 00 00 00 00 | ...............|virtio_mmio: virtio_mmio_write offset 0x50 value 0x2
  virtio_mmio: virtio_mmio setting IRQ 1

  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  0010: 00 12 34 00 00 00 00 00 00 00 00 00 00 00 00 00 |..4.............|
  0020: 00 00 00 00 00 00 00 00 00 00 00 08 2f 64 65 76 |............/dev|
  0030: 2f 73 64 61 00 00 00 03 6d 62 72 00             |/sda....mbr.    |
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x2
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0
  virtio_mmio: virtio_mmio_write offset 0x50 value 0x2
  virtio_mmio: virtio_mmio setting IRQ 1
  virtio_mmio: virtio_mmio_read offset 0x60
  virtio_mmio: virtio_mmio_write offset 0x64 value 0x1
  virtio_mmio: virtio_mmio setting IRQ 0

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