Trace these operations on two memory listeners.  It helps to verify the
new memory listener fix, and good to keep them there.
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180122060244.29368-2-peterx@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

It helps ASAN to detect more leaks on coroutine stacks, and to get rid
of some extra warnings.

Before:

tests/test-coroutine -p
/basic/lifecycle
/basic/lifecycle: ==20781==WARNING: ASan doesn't fully support
makecontext/swapcontext functions and may produce false positives in
some cases!
==20781==WARNING: ASan is ignoring requested __asan_handle_no_return:
stack top: 0x7ffcb184d000; bottom 0x7ff6c4cfd000; size: 0x0005ecb50000
(25446121472)
False positive error reports may follow
For details see https://github.com/google/sanitizers/issues/189
OK

After:

tests/test-coroutine -p /basic/lifecycle
/basic/lifecycle: ==21110==WARNING: ASan doesn't fully support
makecontext/swapcontext functions and may produce false positives in
some cases!
OK

A similar work would need to be done for sigaltstack & windows fibers
to have similar coverage. Since ucontext is preferred, I didn't bother
checking the other coroutine implementations for now.

Update travis to fix the build with ASAN annotations.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180116151152.4040-4-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Typical slowdown introduced by AddressSanitizer is 2x.
UBSan shouldn't have much impact on runtime cost.

Enable it by default when --enable-debug, unless --disable-sanitizers.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180116151152.4040-3-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

gcc 5.4.0-6ubuntu1~16.04.5 build with UBSAN enabled error:

  CC      hw/display/exynos4210_fimd.o
/home/petmay01/linaro/qemu-for-merges/hw/display/exynos4210_fimd.c: In
function ‘fimd_get_buffer_id’:
/home/petmay01/linaro/qemu-for-merges/hw/display/exynos4210_fimd.c:1105:5:
error: case label does not reduce to an integer constant
     case FIMD_WINCON_BUF2_STAT:

Because FIMD_WINCON_BUF2_STAT case contains an integer
overflow, use U suffix to get the unsigned type.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180116151152.4040-2-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The inet_parse() function looks for 'ipv4' and 'ipv6' flags, but only
treats them as bare bool flags. The normal QemuOpts parsing would allow
on/off values to be set too.

This updates inet_parse() so that its handling of the 'ipv4' and 'ipv6'
flags matches that done by QemuOpts.

This impacts the NBD block driver parsing the legacy filename syntax and
the migration code parsing the socket scheme.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Message-Id: <20180125171412.21627-1-berrange@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

We dropped support for ia64 host CPUs in the 2.11 release (removing
the TCG backend for it, and advertising the support as being
completely removed in the changelog).  However there are a few bits
and pieces of code still floating about.  Remove those, too.

We can drop the check in configure for "ia64 or hppa host?"
entirely, because we don't support hppa hosts either any more.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <1516897189-11035-1-git-send-email-peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Add the BSD license there.
Reported-by: NIzik Eidus <izik@veertu.com>
Message-Id: <20180123123639.35255-3-izik@veertu.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hvf.c and vmx.h contain code from hvdos.c that is released as public domain:

from hvdos github: https://github.com/mist64/hvdos

"License

See LICENSE.txt (2-clause-BSD).

In order to simplify use of this code as a template, you can consider any parts from "hvdos.c" and "interface.h" as being in the public domain."
Signed-off-by: NIzik Eidus <izik@veertu.com>
Message-Id: <20180123123639.35255-2-izik@veertu.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The i2c core and the at24c EEPROM should only be compiled and linked
on the machines that support i2c. Otherwise it's quite strange to see
the at24c-eeprom to be "available" on qemu-system-s390x for example.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1516634853-15883-1-git-send-email-thuth@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The memory-internal.h header claims that it is for "obsolete
exec.c functions" which "will be removed soon". This statement
was added in 2011, six years ago, but the header is still here.
(Admittedly none of the prototypes added in commit 67d95c15
are still in the header.)

It's convenient to have a place to put prototypes for functions
which are used internally to the various .c files of the memory
system or by the accel/tcg code, which is inevitably fairly
closely coupled. So keep the header but update the comments to
reflect what we're actually using it for.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <1511276888-17834-1-git-send-email-peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This is required otherwise python complains because of the
accentuated letter in Alex's last name:

Traceback (most recent call last):
  File "scripts/qemu-gdb.py", line 29, in <module>
    from qemugdb import aio, mtree, coroutine, tcg, timers
  File "scripts/qemugdb/timers.py", line 1
SyntaxError: Non-ASCII character '\xc3' in file scripts/qemugdb/timers.py
 on line 1, but no encoding declared;
 see http://www.python.org/peps/pep-0263.html for details
Signed-off-by: NGreg Kurz <groug@kaod.org>
Message-Id: <151629549711.18276.15497684562308683805.stgit@bahia.lan>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Since commit e5dc1a6c, QEMU aborts on exit if completion was used
in the monitor:

*** Error in `obj/ppc64-softmmu/qemu-system-ppc64': double free or
 corruption (fasttop): 0x00000100331069d0 ***

 /home/greg/Work/qemu/qemu-spapr/util/readline.c:514
 /home/greg/Work/qemu/qemu-spapr/monitor.c:586
 /home/greg/Work/qemu/qemu-spapr/monitor.c:4125
 argv=<optimized out>, envp=<optimized out>) at
 /home/greg/Work/qemu/qemu-spapr/vl.c:4795

Completion strings are not persistent accross completions (why would
they?). They are allocated under readline_completion(), which already
takes care of freeing them before returning.

Maybe all completion related bits should be moved out of ReadLineState
to a dedicated structure ?

In the meantime, let's drop the offending lines from readline_free()
to fix the crash.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Message-Id: <151627206353.4505.4602428849861610759.stgit@bahia.lan>
Fixes: e5dc1a6cSigned-off-by: NPaolo Bonzini <pbonzini@redhat.com>

glib reported error when pty chardev used:

$ ./qemu-system-x86_64 -chardev pty,id=foo -device isa-serial,chardev=foo
qemu-system-x86_64: -chardev pty,id=foo: char device redirected to /dev/pts/2 (label foo)
(qemu-system-x86_64:27885): GLib-CRITICAL **: g_source_unref: assertion 'source != NULL' failed
(qemu-system-x86_64:27885): GLib-CRITICAL **: g_source_unref: assertion 'source != NULL' failed

This patch fixes that.

Fixes: 2c716ba1 ("chardev: introduce qemu_chr_timeout_add_ms()")
CC: Paolo Bonzini <pbonzini@redhat.com>
Reported-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180118052049.31119-1-peterx@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Coverity doesn't like the ignored return value introduced in
9d3b1551 (hw/block: Fix the return type), and other callers are
converted already in ceff3e1f.

This one was added lately in d9bcd6f7 and missed the train. Do it
now.
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-Id: <20180118025245.13042-1-famz@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

We should set ioeventfd_update_pending same as memory_region_update_pending.
Signed-off-by: Nlinzhecheng <linzc@zju.edu.cn>
Message-Id: <1515934519-16158-1-git-send-email-linzc@zju.edu.cn>
Cc: qemu-stable@nongnu.org
Fixes: ade9c1aaSigned-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Improve hugepage allocation failure message, indicating
what is happening to the user.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

Message-Id: <20180115201700.GA4439@amt.cnet>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This adds a tracepoint to trace the KVM_SET_USER_MEMORY_REGION ioctl
parameters which is quite useful for debugging VFIO memory regions
being actually registered with KVM.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20171215052326.21386-1-aik@ozlabs.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

changes generated using the following Coccinelle patch:

  @@
  type DeviceParentClass;
  DeviceParentClass *pc;
  DeviceClass *dc;
  identifier parent_fn;
  identifier child_fn;
  @@
  (
  +device_class_set_parent_realize(dc, child_fn, &pc->parent_fn);
  -pc->parent_fn = dc->realize;
  ...
  -dc->realize = child_fn;
  |
  +device_class_set_parent_unrealize(dc, child_fn, &pc->parent_fn);
  -pc->parent_fn = dc->unrealize;
  ...
  -dc->unrealize = child_fn;
  |
  +device_class_set_parent_reset(dc, child_fn, &pc->parent_fn);
  -pc->parent_fn = dc->reset;
  ...
  -dc->reset = child_fn;
  )
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180114020412.26160-4-f4bug@amsat.org>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Acked-by: NDavid Gibson <david@gibson.dropbear.id.au>
Acked-by: NCornelia Huck <cohuck@redhat.com>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

QOM API learning curve is quite hard, in particular when devices inherit from
abstract parent.
To be more explicit about when a device class change the parent hooks, add few
helpers hoping a device class_init() will be easier to understand.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180114020412.26160-3-f4bug@amsat.org>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

following the DeviceRealize and DeviceUnrealize typedefs,
this unify a bit the new QOM API.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180114020412.26160-2-f4bug@amsat.org>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Signed-off-by: NJay Zhou <jianjay.zhou@huawei.com>
Message-Id: <1515043788-38300-1-git-send-email-jianjay.zhou@huawei.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

ui: use QIONetListener in vnc, bugfixes for sdl1 and vnc.

# gpg: Signature made Fri 02 Feb 2018 07:17:36 GMT
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/ui-20180202-pull-request:
  ui: correctly advance output buffer when writing SASL data
  ui: convert VNC server to QIONetListener
  ui: fix mixup between qnum and qcode in SDL1 key handling
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

virtio-gpu: disallow vIOMMU

# gpg: Signature made Fri 02 Feb 2018 08:31:52 GMT
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/vga-20180202-pull-request:
  virtio-gpu: disallow vIOMMU
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

This series is mostly about 9p request cancellation. It fixes a
long standing bug (read "specification violation") where the server
would send an invalid response when the client has cancelled an
in-flight request. This was causing annoying spurious EINTR returns
in linux. The fix comes with some related testing in QTEST.

Other patches are code cleanup and improvements.

# gpg: Signature made Fri 02 Feb 2018 10:16:03 GMT
# gpg:                using RSA key 71D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>"
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>"
# gpg:                 aka "[jpeg image of size 3330]"
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/for-upstream:
  tests/virtio-9p: explicitly handle potential integer overflows
  tests: virtio-9p: add FLUSH operation test
  libqos/virtio: return length written into used descriptor
  tests: virtio-9p: add WRITE operation test
  tests: virtio-9p: add LOPEN operation test
  tests: virtio-9p: use the synth backend
  tests: virtio-9p: wait for completion in the test code
  tests: virtio-9p: move request tag to the test functions
  9pfs: Correctly handle cancelled requests
  9pfs: drop v9fs_register_transport()
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

audio: two small fixes.

# gpg: Signature made Fri 02 Feb 2018 07:49:20 GMT
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/audio-20180202-pull-request:
  hw/audio/sb16.c: change dolog() to qemu_log_mask()
  hw/audio/wm8750: move WM8750 declarations from i2c/i2c.h to audio/wm8750.h
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Lots of litte miscellaneous fixes for the IPMI code, plus
add me as the IPMI maintainer.

# gpg: Signature made Thu 01 Feb 2018 18:44:55 GMT
# gpg:                using RSA key 61F38C90919BFF81
# gpg: Good signature from "Corey Minyard <cminyard@mvista.com>"
# gpg:                 aka "Corey Minyard <minyard@acm.org>"
# gpg:                 aka "Corey Minyard <corey@minyard.net>"
# gpg:                 aka "Corey Minyard <minyard@mvista.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: FD0D 5CE6 7CE0 F59A 6688  2686 61F3 8C90 919B FF81

* remotes/cminyard/tags/for-release-20180201:
  ipmi: Allow BMC device properties to be set
  ipmi: disable IRQ and ATN on an external disconnect
  ipmi: Fix macro issues
  ipmi: Add the platform event message command
  ipmi: Don't set the timestamp on add events that don't have it
  ipmi: Fix SEL get/set time commands
  Add maintainer for the IPMI code
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

# gpg: Signature made Thu 01 Feb 2018 11:15:42 GMT
# gpg:                using RSA key DAE8E10975969CE5
# gpg: Good signature from "Marc-André Lureau <marcandre.lureau@redhat.com>"
# gpg:                 aka "Marc-André Lureau <marcandre.lureau@gmail.com>"
# Primary key fingerprint: 87A9 BD93 3F87 C606 D276  F62D DAE8 E109 7596 9CE5

* remotes/elmarco/tags/dump-pull-request:
  dump-guest-memory.py: skip vmcoreinfo section if not available
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

The idea is to send a victim request that will possibly block in the
server and to send a flush request to cancel the victim request.

This patch adds two test to verifiy that:
- the server does not reply to a victim request that was actually
  cancelled
- the server replies to the flush request after replying to the
  victim request if it could not cancel it

9p request cancellation reference:

http://man.cat-v.org/plan_9/5/flushSigned-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
(groug, change the test to only write a single byte to avoid
        any alignment or endianess consideration)

When a 9p request is flushed (ie, cancelled) by the guest, the device
is expected to simply mark the request as used, without sending a 9p
reply (ie, without writing anything into the used buffer).

To be able to test this, we need access to the length written by the
device into the used descriptor. This patch adds a uint32_t * argument
to qvirtqueue_get_buf() and qvirtio_wait_used_elem() for this purpose.

All existing users are updated accordingly.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

# gpg: Signature made Thu 01 Feb 2018 04:05:22 GMT
# gpg:                using RSA key BDBE7B27C0DE3057
# gpg: Good signature from "Jeffrey Cody <jcody@redhat.com>"
# gpg:                 aka "Jeffrey Cody <jeff@codyprime.org>"
# gpg:                 aka "Jeffrey Cody <codyprime@gmail.com>"
# Primary key fingerprint: 9957 4B4D 3474 90E7 9D98  D624 BDBE 7B27 C0DE 3057

* remotes/cody/tags/block-pull-request:
  iotests: Make 200 run on tmpfs
  block/ssh: fix possible segmentation fault when .desc is not null-terminated
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

virtio-gpu has special code path that bypassed vIOMMU protection.  So
for now let's disable iommu_platform for the device until we fully
support that (if needed).

After the patch, both virtio-vga and virtio-gpu won't allow to boot with
iommu_platform parameter set.

CC: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-id: 20180131040401.3550-1-peterx@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

Changes all the occurrances of dolog() to qemu_log_mask().
Signed-off-by: NJohn Arbuckle <programmingkidx@gmail.com>
Message-id: 20180201172744.7504-1-programmingkidx@gmail.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

while here use TYPE_WM8750 and declare a data_req_cb() typedef.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170919123053.32675-1-f4bug@amsat.org
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

In this previous commit:

  commit 8f61f1c5
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Mon Dec 18 19:12:20 2017 +0000

    ui: track how much decoded data we consumed when doing SASL encoding

I attempted to fix a flaw with tracking how much data had actually been
processed when encoding with SASL. With that flaw, the VNC server could
mistakenly discard queued data that had not been sent.

The fix was not quite right though, because it merely decremented the
vs->output.offset value. This is effectively discarding data from the
end of the pending output buffer. We actually need to discard data from
the start of the pending output buffer. We also want to free memory that
is no longer required. The correct way to handle this is to use the
buffer_advance() helper method instead of directly manipulating the
offset value.
Reported-by: NLaszlo Ersek <lersek@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Message-id: 20180201155841.27509-1-berrange@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

The VNC server already has the ability to listen on multiple sockets.
Converting it to use the QIONetListener APIs though, will reduce the
amount of code in the VNC server and improve the clarity of what is
left.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Message-id: 20180201164514.10330-1-berrange@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

The previous commit:

  commit 2ec78706
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Wed Jan 17 16:47:15 2018 +0000

    ui: convert GTK and SDL1 frontends to keycodemapdb

changed the x_keymap.c keymap so that its target was qcodes instead of
qnums. It updated the GTK frontend to take account of this change, but
forgot to update the SDL1 frontend. Thus the SDL frontend was getting
qcodes but dispatching them as if they were qnums. IOW, keyboard input
was completely hosed with SDL1. Since the keyboard layout tables are
still all based on qnums, it is easier to just keep SDL1 using qnums as
it will be deleted in a few releases time.
Reported-by: NBALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>
Tested-by: NBALATON Zoltan <balaton@eik.bme.hu>
Message-id: 20180201180033.14255-1-berrange@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

Trivial test of a successful write.
Signed-off-by: NGreg Kurz <groug@kaod.org>
(groug, handle potential overflow when computing request size,
        add missing g_free(buf),
        backend handles one written byte at a time to validate
        the server doesn't do short-reads)
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

Trivial test of a successful open.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>

The purpose of virtio-9p-test is to test the virtio-9p device, especially
the 9p server state machine. We don't really care what fsdev backend we're
using. Moreover, if we want to be able to test the flush request or a
device reset with in-flights I/O, it is close to impossible to achieve
with a physical backend because we cannot ask it reliably to put an I/O
on hold at a specific point in time.

Fortunately, we can do that with the synthetic backend, which allows to
register callbacks on read/write accesses to a specific file. This will
be used by a later patch to test the 9P flush request.

The walk request test is converted to using the synth backend.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>