Re: [Qemu-devel] [PATCH] cpus: Fix event order on resume of stopped guest

[Kevin Wolf <kwolf@redhat.com>]

Am 23.04.2018 um 17:47 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
> 
> > Am 23.04.2018 um 10:45 hat Markus Armbruster geschrieben:
> >> When resume of a stopped guest immediately runs into block device
> >> errors, the BLOCK_IO_ERROR event is sent before the RESUME event.
> >> 
> >> Reproducer:
> >> 
> >> 1. Create a scratch image
> >>    $ dd if=/dev/zero of=scratch.img bs=1M count=100
> >> 
> >>    Size doesn't actually matter.
> >> 
> >> 2. Prepare blkdebug configuration:
> >> 
> >>    $ cat >blkdebug.conf <<EOF
> >>    [inject-error]
> >>    event = "write_aio"
> >>    errno = "5"
> >>    EOF
> >> 
> >>    Note that errno 5 is EIO.
> >> 
> >> 3. Run a guest with an additional scratch disk, i.e. with additional
> >>    arguments
> >>    -drive if=none,id=scratch-drive,format=raw,werror=stop,file=blkdebug:blkdebug.conf:scratch.img
> >>    -device virtio-blk-pci,id=scratch,drive=scratch-drive
> >> 
> >>    The blkdebug part makes all writes to the scratch drive fail with
> >>    EIO.  The werror=stop pauses the guest on write errors.
> >> 
> >> 4. Connect to the QMP socket e.g. like this:
> >>    $ socat UNIX:/your/qmp/socket READLINE,history=$HOME/.qmp_history,prompt='QMP> '
> >> 
> >>    Issue QMP command 'qmp_capabilities':
> >>    QMP> { "execute": "qmp_capabilities" }
> >> 
> >> 5. Boot the guest.
> >> 
> >> 6. In the guest, write to the scratch disk, e.g. like this:
> >> 
> >>    # dd if=/dev/zero of=/dev/vdb count=1
> >> 
> >>    Do double-check the device specified with of= is actually the
> >>    scratch device!
> >> 
> >> 7. Issue QMP command 'cont':
> >>    QMP> { "execute": "cont" }
> >> 
> >> After step 6, I get a BLOCK_IO_ERROR event followed by a STOP event.  Good.
> >> 
> >> After step 7, I get BLOCK_IO_ERROR, then RESUME, then STOP.  Not so
> >> good; I'd expect RESUME, then BLOCK_IO_ERROR, then STOP.
> >
> > Do you want to rephrase this in the form of a script for qemu-iotests?
> >
> > I suppose the 'dd' line can be replaced by a 'qemu-io' monitor command.
> 
> Makes sense, but I'm quite pretty much a noob there.  Perhaps I can copy
> an existing test and hack it up.  Which one would you recommend?

Depends on how much control you actually need for this test. At first
sight, it might be enough to copy one of the tests implementing a
run_qemu() function. These are tests that do essentially this:

    qemu-system-x86_64 -qmp stdio <<EOF
    ...commands here....
    EOF

This is all you need if you don't have a reason to wait for or even
parse QMP results. (The results end up in stdout, so they are validated
with the usual diffing.)

If you need a bit more, copy one of the tests that use ./common.qemu.
This is a bit more complex but allows you to wait for expected QMP
results before you continue with the next action. Probably you don't
need this here.

(And if even that is not powerful enough, Python test cases with
iotests.py are what you want. Almost certainly overkill for this one.)

Kevin