[Qemu-devel] 100% CPU when sockfd is half-closed and unexpected behavior for qemu_co_send()

[Liu Yuan <namei.unix@gmail.com>]

Hi List,
  This problem can be reproduced by:
  1. start a sheepdog cluster and create a volume 'test'*
  2. attach 'test' to a bootable image like
     $ qemu -hda image -drive if=virtio,file=sheepdog:test
  3. pkill sheep # create a half-closed situation

I have straced it that QEMU is busy doing nonsense read/write() after
select() in os_host_main_loop_wait(). I have no knowledge of
glib_select_xxx, so someone please help fix it.

Another unexpected behavior is that qemu_co_send() will send data
successfully for the half-closed situation, even the other end is
completely down. I think the *expected* behavior is that we get notified
by a HUP and close the affected sockfd, then qemu_co_send() will not
send any data, then the caller of qemu_co_send() can handle error case.

I don't know which one I should Cc, so I only include Stefan in.

* You can easily start up a one node sheepdog cluster as following:
 $ git clone https://github.com/collie/sheepdog.git
 $ cd sheepdog
 $ apt-get install liburcu-dev
 $ ./autogen.sh; ./configure --disable-corosync;make
 #start up a one node sheep cluster
 $ mkdir store;./sheep/sheep store -c local
 $ collie/collie cluster format -c 1
 #create a volume named test
 $ collie/collie vdi create test 1G

Thanks,
Yuan