fixes for 2.9-rc1, plus removal of -mno-cygwin references

# gpg: Signature made Mon 20 Mar 2017 11:25:07 GMT
# gpg:                using RSA key 0xBFFBD25F78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>"
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  hax: fix breakage in locking
  configure: remove Cygwin
  xen: do not build backends for targets that do not support xen
  qemu-ga: obey LISTEN_PID when using systemd socket activation
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

sdl is probed before audio, so we can simply look at $sdl so see
whenever we have support or not.  Throw an error in case sdl audio
is requested without sdl being available.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Tested-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1490000743-3615-1-git-send-email-kraxel@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

The Cygwin target is really compiling for native Win32 with -mno-cygwin.
Except, GCC 4.7.0 has finally removed the long deprecated -mno-cygwin
option, and that happened about five years ago.

Let it rest in peace.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NStefan Weil <sw@weilnetz.de>
Message-id: 20170317160811.28370-1-pbonzini@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

MIPS patches 2017-03-20

Changes:
* Fix clang warnings
* Fix delay slot detection in gen_msa_branch()
* Fix rc4030 interval timer
* Fix rc4030 to tranlate memory accesses only when they occur
* Fix 4c4030 a mixed declarations and code warning
* Update MAINTAINERS file

# gpg: Signature made Mon 20 Mar 2017 12:46:01 GMT
# gpg:                using RSA key 0x2238EB86D5F797C2
# gpg: Good signature from "Yongbok Kim <yongbok.kim@imgtec.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 8600 4CF5 3415 A5D9 4CFA  2B5C 2238 EB86 D5F7 97C2

* remotes/yongbok/tags/mips-20170320:
  MAINTAINERS: update for MIPS devices
  dma/rc4030: fix a mixed declarations and code warning
  dma/rc4030: translate memory accesses only when they occur
  dma: rc4030: limit interval timer reload value
  target/mips: fix delay slot detection in gen_msa_branch()
  target-mips: replace few LOG_DISAS() with trace points
  target-mips: replace break by goto cp0_unimplemented
  target-mips: log bad coprocessor0 register accesses with LOG_UNIMP
  target-mips: remove old & unuseful comments
  target-mips: fix compiler warnings (clang 5)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm queue:
 * fix MSR/MRS decoding for M profile CPUs

# gpg: Signature made Mon 20 Mar 2017 12:53:26 GMT
# gpg:                using RSA key 0x3C2525ED14360CDE
# gpg: Good signature from "Peter Maydell <peter.maydell@linaro.org>"
# gpg:                 aka "Peter Maydell <pmaydell@gmail.com>"
# gpg:                 aka "Peter Maydell <pmaydell@chiark.greenend.org.uk>"
# Primary key fingerprint: E1A5 C593 CD41 9DE2 8E83  15CF 3C25 25ED 1436 0CDE

* remotes/pmaydell/tags/pull-target-arm-20170320:
  arm: Fix APSR writes via M profile MSR
  arm: Enforce should-be-1 bits in MRS decoding
  arm: Don't decode MRS(banked) or MSR(banked) for M profile
  arm: HVC and SMC encodings don't exist for M profile
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Our implementation of writes to the APSR for M-profile via the MSR
instruction was badly broken.

First and worst, we had the sense wrong on the test of bit 2 of the
SYSm field -- this is supposed to request an APSR write if bit 2 is 0
but we were doing it if bit 2 was 1.  This bug was introduced in
commit 58117c9b, so hasn't been in a QEMU release.

Secondly, the choice of exactly which parts of APSR should be written
is defined by bits in the 'mask' field.  We were not passing these
through from instruction decode, making it impossible to check them
in the helper.

Pass the mask bits through from the instruction decode to the helper
function and process them appropriately; fix the wrong sense of the
SYSm bit 2 check.

Invalid mask values and invalid combinations of mask and register
number are UNPREDICTABLE; we choose to treat them as if the mask
values were valid.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1487616072-9226-5-git-send-email-peter.maydell@linaro.org
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>

The MRS instruction requires that bits [19..16] are all 1s, and for
A/R profile also that bits [7..0] are all 0s.  At this point in the
decode tree we have checked all of the rest of the instruction but
were allowing these to be any value.  If these bits are not set then
the result is architecturally UNPREDICTABLE, but choosing to UNDEF is
more helpful to the user and avoids unexpected odd behaviour if the
encodings are used for some purpose in future architecture versions.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Message-id: 1487616072-9226-4-git-send-email-peter.maydell@linaro.org

M profile doesn't have the MSR(banked) and MRS(banked) instructions
and uses the encodings for different kinds of M-profile MRS/MSR.
Guard the relevant bits of the decode logic to make sure we don't
accidentally fall into them by accident on M-profile.

(The bit being checked for this (bit 5) is part of the SYSm field on
M-profile, but since no currently allocated system registers have
encodings with bit 5 of SYSm set, this hasn't been a problem in
practice.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Message-id: 1487616072-9226-3-git-send-email-peter.maydell@linaro.org

M profile doesn't have the HVC or SMC encodings, so make them always
UNDEF rather than generating calls to helper functions that assume
A/R profile.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Message-id: 1487616072-9226-2-git-send-email-peter.maydell@linaro.org

use qemu_mutex_lock_iothread consistently in qemu_hax_cpu_thread_fn() as
done in other _thread_fn functions, instead of grabbing directly the
BQL. This way we ensure that iothread_locked is properly set.

On v2.9.0-rc0, QEMU was dying in an assertion in the mutex code when
running with '--enable-hax' either on OSX or Windows. This bug was triggered
since the code modification for multithreading added new usages of
qemu_mutex_iothread_locked.
This fixes the breakage on both platforms, I can now run again a full
Chromium OS image with HAX kernel acceleration.
Signed-off-by: NVincent Palatin <vpalatin@chromium.org>
Message-Id: <20170320101549.150076-1-vpalatin@chromium.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Add myself to MIPSSIM and new entry for Fulong 2E.
Add an entry for Boston machine (Paul Burton).

cc: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>

Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>
Reviewed-by: NHervé Poussineau <hpoussin@reactos.org>

This simplifies the code a lot, and this fixes big memory leaks
introduced in a3d586f7

Windows NT is now able to boot without using gigabytes of ram on the host.
Signed-off-by: NHervé Poussineau <hpoussin@reactos.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

The JAZZ RC4030 chipset emulator has a periodic timer and
associated interval reload register. The reload value is used
as divider when computing timer's next tick value. If reload
value is large, it could lead to divide by zero error. Limit
the interval reload value to avoid it.
Reported-by: NHuawei PSIRT <psirt@huawei.com>
Signed-off-by: NPrasad J Pandit <pjp@fedoraproject.org>
Tested-by: NHervé Poussineau <hpoussin@reactos.org>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

It is unnecessary to test R6 from delay/forbidden slot check
in gen_msa_branch().

https://bugs.launchpad.net/qemu/+bug/1663287Reported-by: NBrian Campbell <bacam@z273.org.uk>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

this fixes many warnings like:

target/mips/translate.c:6253:13: warning: Value stored to 'rn' is never read
            rn = "invalid sel";
            ^    ~~~~~~~~~~~~~

Reported-by: Clang Static Analyzer
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

static code analyzer complain:

target/mips/helper.c:453:5: warning: Function call argument is an uninitialized value
    qemu_log_mask(CPU_LOG_MMU,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~

'physical' and 'prot' are uninitialized if 'ret' is not TLBRET_MATCH.

Reported-by: Clang Static Analyzer
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NYongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: NYongbok Kim <yongbok.kim@imgtec.com>

One bugfix for device plug/unplug and migration in the
channel subsystem code.

# gpg: Signature made Mon 20 Mar 2017 08:45:59 GMT
# gpg:                using RSA key 0xDECF6B93C6F02FAF
# gpg: Good signature from "Cornelia Huck <huckc@linux.vnet.ibm.com>"
# gpg:                 aka "Cornelia Huck <cornelia.huck@de.ibm.com>"
# Primary key fingerprint: C3D0 D66D C362 4FF6 A8C0  18CE DECF 6B93 C6F0 2FAF

* remotes/cohuck/tags/s390x-20170320:
  s390x/css: reassign subchannel if schid is changed after migration
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

fixes for 2.9: vnc, cirrus, tcg display updates.

# gpg: Signature made Mon 20 Mar 2017 08:52:34 GMT
# gpg:                using RSA key 0x4CB6D8EED3E87138
# 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/pull-fixes-20170320-1:
  vnc: fix a qio-channel leak
  cirrus: fix off-by-one in cirrus_bitblt_rop_bkwd_transp_*_16
  ui/console: ensure graphic updates don't race with TCG vCPUs
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

The subchannel is a means to access a device. While the device number is
assigned by the administrator, the subchannel number is assigned by
the channel subsystem in an ascending order on cold and hot plug.
When doing unplug and replug operations, the same device may end up on
a different subchannel; for example

- We start with a device fe.1.2222, which ends up at subchannel
  fe.1.0000.
- Now we detach the device, attach a device fe.1.3333 (which would get
  the now-free subchannel fe.1.0000), re-attach fe.1.2222 (which ends
  up at subchannel fe.1.0001) and detach fe.1.3333.
- We now have the same device (fe.1.2222) available to the guest; it
  just shows up on a different subchannel.

In such a case, the subchannel numbers are different from what a
QEMU would create during cold plug when parsing the command line.

As this would cause a guest visible change on migration, we do restore
the source system's value of the subchannel number on load.

So we are now fine from the guest perspective. From the host
perspective this will cause an inconsistent state in our internal data
structures, though.

For example, the subchannel 0 might not be at array position 0. This will
lead to problems when we continue doing hot (un/re) plug operations.

Let's fix this by cleaning up our internal data structures.
Reported-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NDong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>

Spotted by ASAN.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NDaniel P. Berrange <berrange@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170317092802.17973-1-marcandre.lureau@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

The Cygwin target is really compiling for native Win32 with -mno-cygwin.
Except, GCC 4.7.0 has finally removed the long deprecated -mno-cygwin
option, and that happened about five years ago.

Let it rest in peace.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Change Makefile.objs to use CONFIG_XEN instead of CONFIG_XEN_BACKEND, so
that the Xen backends are only built for targets that support Xen.

Set CONFIG_XEN in the toplevel Makefile to ensure that files that are
built only once pick up Xen support properly.
Signed-off-by: NStefano Stabellini <stefano@aporeto.com>
Tested-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NGreg Kurz <groug@kaod.org>
CC: pbonzini@redhat.com
CC: peter.maydell@linaro.org
CC: rth@twiddle.net
CC: stefanha@redhat.com
Message-Id: <1489694518-16978-1-git-send-email-sstabellini@kernel.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

qemu-ga's socket activation support was not obeying the LISTEN_PID
environment variable, which avoids that a process uses a socket-activation
file descriptor meant for its parent.

Mess can for example ensue if a process forks a children before consuming
the socket-activation file descriptor and therefore setting O_CLOEXEC
on it.

Luckily, qemu-nbd also got socket activation code, and its copy does
support LISTEN_PID.  Some extra fixups are needed to ensure that the
code can be used for both, but that's what this patch does.  The
main change is to replace get_listen_fds's "consume" argument with
the FIRST_SOCKET_ACTIVATION_FD macro from the qemu-nbd code.

Cc: "Richard W.M. Jones" <rjones@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Add a const qom link between the CPU and the IIC instead
of passing the CPU link through a qom property.
Signed-off-by: NMarek Vasut <marex@denx.de>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Message-id: 20170317210627.23532-1-marex@denx.de
Cc: Alexander Graf <agraf@suse.de>
Cc: Chris Wulff <crwulff@gmail.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jeff Da Silva <jdasilva@altera.com>
Cc: Ley Foon Tan <lftan@altera.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Sandra Loosemore <sandra@codesourcery.com>
Cc: Yves Vandervennet <yvanderv@altera.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/xtensa fixes for 2.9:

- fix build failure when FDT support is not enabled;
- correctly pass command line arguments to semihosting guests.

# gpg: Signature made Fri 17 Mar 2017 18:14:01 GMT
# gpg:                using RSA key 0x51F9CC91F83FA044
# gpg: Good signature from "Max Filippov <filippov@cadence.com>"
# gpg:                 aka "Max Filippov <max.filippov@cogentembedded.com>"
# gpg:                 aka "Max Filippov <jcmvbkbc@gmail.com>"
# Primary key fingerprint: 2B67 854B 98E5 327D CDEB  17D8 51F9 CC91 F83F A044

* remotes/xtensa/tags/20170317-xtensa:
  target/xtensa: fix semihosting argc/argv implementation
  target/xtensa: xtfpga: load DTB only when FDT support is enabled
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

si_band is not found in OpenBSD.   It is marked as obsolescent in
POSIX, so we can delete it without any remorse.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20170317152214.6148-1-pbonzini@redhat.com
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

EPROTO is not found in OpenBSD.   We usually use EIO when no better
errno is available, do that here too.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20170317152412.8472-1-pbonzini@redhat.com
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Block layer fixes for 2.9.0-rc1

# gpg: Signature made Fri 17 Mar 2017 12:06:04 GMT
# gpg:                using RSA key 0x7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream:
  block: quiesce AioContext when detaching from it
  thread-pool: add missing qemu_bh_cancel in completion function
  block: Propagate error in bdrv_open_backing_file
  blockdev: fix bitmap clear undo
  block: Always call bdrv_child_check_perm first
  file-posix: Don't leak fd in hdev_get_max_segments
  replication: clarify permissions
  file-posix: clean up max_segments buffer termination
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Block patches for 2.9-rc1

# gpg: Signature made Fri Mar 17 12:59:20 2017 CET
# gpg:                using RSA key 0xF407DB0061D5CF40
# gpg: Good signature from "Max Reitz <mreitz@redhat.com>"
# Primary key fingerprint: 91BE B60A 30DB 3E88 57D1  1829 F407 DB00 61D5 CF40

* mreitz/tags/pull-block-2017-03-17:
  block: quiesce AioContext when detaching from it
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

While it is true that bdrv_set_aio_context only works on a single
BlockDriverState subtree (see commit message for 53ec73e2, "block: Use
bdrv_drain to replace uncessary bdrv_drain_all", 2015-07-07), it works
at the AioContext level rather than the BlockDriverState level.

Therefore, it is also necessary to trigger pending bottom halves too,
even if no requests are pending.

For NBD this ensures that the aio_co_schedule of a previous call to
nbd_attach_aio_context is completed before detaching from the old
AioContext; it fixes qemu-iotest 094.  Another similar bug happens
when the VM is stopped and the virtio-blk dataplane irqfd is torn down.
In this case it's possible that guest I/O gets stuck if notify_guest_bh
was scheduled but doesn't run.

Calling aio_poll from another AioContext is safe if non-blocking; races
such as the one mentioned in the commit message for c9d1a561 ("block:
only call aio_poll on the current thread's AioContext", 2016-10-28)
are a concern for blocking calls.

I considered other options, including:

- moving the bs->wakeup mechanism to AioContext, and letting the caller
check.  This might work for virtio which has a clear place to wakeup
(notify_place_bh) and check the condition (virtio_blk_data_plane_stop).
For aio_co_schedule I couldn't find a clear place to check the condition.

- adding a dummy oneshot bottom half and waiting for it to trigger.
This has the complication that bottom half list is LIFO for historical
reasons.  There were performance issues caused by bottom half ordering
in the past, so I decided against it for 2.9.

Fixes: 99723548Reported-by: NMax Reitz <mreitz@redhat.com>
Reported-by: NHalil Pasic <pasic@linux.vnet.ibm.com>
Tested-by: NHalil Pasic <pasic@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-id: 20170314111157.14464-2-pbonzini@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

commit 3c80ca15 fixed a deadlock scenarion with nested aio_poll invocations.

However, the rescheduling of the completion BH introcuded unnecessary spinning
in the main-loop. On very fast file backends this can even lead to the
"WARNING: I/O thread spun for 1000 iterations" message popping up.

Callgrind reports about 3-4% less instructions with this patch running
qemu-img bench on a ramdisk based VMDK file.

Fixes: 3c80ca15
Cc: qemu-stable@nongnu.org
Signed-off-by: NPeter Lieven <pl@kamp.de>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

Only undo the action if we actually prepared the action.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

bdrv_child_set_perm alone is not very usable because the caller must
call bdrv_child_check_perm first. This is already encapsulated
conveniently in bdrv_child_try_set_perm, so remove the other prototypes
from the header and fix the one wrong caller, block/mirror.c.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

This fixes a leaked fd introduced in commit 9103f1ce.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

Even if hidden_disk, secondary_disk are backing files, they all need
write permissions in replication scenario. Otherwise we will encouter
below exceptions on secondary side during adding nbd server:

{'execute': 'nbd-server-add', 'arguments': {'device': 'colo-disk', 'writable': true } }
{"error": {"class": "GenericError", "desc": "Conflicts with use by hidden-qcow2-driver as 'backing', which does not allow 'write' on sec-qcow2-driver-for-nbd"}}

CC: Zhang Hailiang <zhang.zhanghailiang@huawei.com>
CC: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
CC: Wen Congyang <wencongyang2@huawei.com>
Signed-off-by: NChanglong Xie <xiecl.fnst@cn.fujitsu.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>