The original code was wrong, because effectively it ignored errors
from kernel, because kernel does not return -1 on error case but
returns -errno, and does not return -EPERM for this particular ioctl.
But in some cases kernel actually returned unsuccessful result,
namely, when the dirty bitmap in requested slot does not exist
it returns -ENOENT. With new code this condition becomes an
error when it shouldn't be.
Revert that patch instead of fixing it properly this late in the
release process. I disagree with this approach, but let's make
things move _somewhere_, instead of arguing endlessly whch of
the 2 proposed fixes is better.
Peter Maydell [Mon, 14 Apr 2014 13:02:12 +0000 (14:02 +0100)]
Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging
acpi: SSDT update
This has a fix by Igor for a regression introduced by
bridge hotplug code.
Expected test files were updated accordingly.
Signed-off-by: Michael S. Tsirkin <[email protected]>
# gpg: Signature made Mon 14 Apr 2014 13:13:35 BST using RSA key ID D28D5469
# gpg: Good signature from "Michael S. Tsirkin <[email protected]>"
# gpg: aka "Michael S. Tsirkin <[email protected]>"
ide: Correct improper smart self test counter reset in ide core.
The SMART self test counter was incorrectly being reset to zero,
not 1. This had the effect that on every 21st SMART EXECUTE OFFLINE:
* We would write off the beginning of a dynamically allocated buffer
* We forgot the SMART history
Fix this.
Igor Mammedov [Sun, 13 Apr 2014 21:55:51 +0000 (23:55 +0200)]
acpi: fix incorrect encoding for 0x{F-1}FFFF
Fix typo in build_append_int() which causes integer
truncation when it's in range 0x{F-1}FFFF by packing it
as WordConst instead of required DWordConst.
In partucular this fixes a regression: hotplug in slots 16,17,18 and 19
didn't work, since SSDT had code like this:
Peter Maydell [Fri, 11 Apr 2014 16:13:52 +0000 (17:13 +0100)]
configure: Make stack-protector test check both compile and link
Since we use the -fstack-protector argument at both compile and
link time in the build, we must check that it works with both
a compile and a link:
* MacOSX only fails in the compile step, not linking
* some gcc cross environments only fail at the link stage (if they
require a libssp and it's not present for some reason)
When VM guest programs multicast addresses for
a virtio net card, it supplies a 32 bit
entries counter for the number of addresses.
These addresses are read into tail portion of
a fixed macs array which has size MAC_TABLE_ENTRIES,
at offset equal to in_use.
To avoid overflow of this array by guest, qemu attempts
to test the size as follows:
- if (in_use + mac_data.entries <= MAC_TABLE_ENTRIES) {
however, as mac_data.entries is uint32_t, this sum
can overflow, e.g. if in_use is 1 and mac_data.entries
is 0xffffffff then in_use + mac_data.entries will be 0.
Qemu will then read guest supplied buffer into this
memory, overflowing buffer on heap.
Peter Maydell [Fri, 11 Apr 2014 13:07:24 +0000 (14:07 +0100)]
Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging
Block patches for 2.0.0-rc3
# gpg: Signature made Fri 11 Apr 2014 13:37:34 BST using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <[email protected]>"
* remotes/kevin/tags/for-upstream:
block-commit: speed is an optional parameter
iscsi: Remember to set ret for iscsi_open in error case
bochs: Fix catalog size check
bochs: Fix memory leak in bochs_open() error path
Max Reitz [Thu, 10 Apr 2014 17:36:25 +0000 (19:36 +0200)]
block-commit: speed is an optional parameter
As speed is an optional parameter for the QMP block-commit command, it
should be set to 0 if not given (as it is undefined if has_speed is
false), that is, the speed should not be limited.
Kevin Wolf [Wed, 9 Apr 2014 10:10:34 +0000 (12:10 +0200)]
bochs: Fix catalog size check
The old check was off by a factor of 512 and didn't consider cases where
we don't get an exact division. This could lead to an out-of-bounds
array access in seek_to_sector().
input: sdl2: Fix relative mode to match SDL1 behavior
Right now relative mode accelerates too fast, and has the 'invisible wall'
problem. SDL2 added an explicit API to handle this use case, so let's use
it.
Peter Maydell [Thu, 10 Apr 2014 22:07:55 +0000 (23:07 +0100)]
Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging
acpi: DSDT update
Two fixes here:
- Test fix to avoid warning with make check.
- Hex file update so people building QEMU
without installing iasl get exactly the same ACPI
as with.
Both should help avoid user confusion.
As it's very easy to check that the produced ACPI
binary didn't change, I think these are very low risk.
Signed-off-by: Michael S. Tsirkin <[email protected]>
# gpg: Signature made Thu 10 Apr 2014 17:09:43 BST using RSA key ID D28D5469
# gpg: Good signature from "Michael S. Tsirkin <[email protected]>"
# gpg: aka "Michael S. Tsirkin <[email protected]>"
Peter Maydell [Wed, 9 Apr 2014 11:04:47 +0000 (12:04 +0100)]
configure: use do_cc when checking for -fstack-protector support
MacOSX clang silently swallows unrecognized -f options when doing a link
with '-framework' also on the command line, so to detect support for
the various -fstack-protector options we must do a plain .c to .o compile,
not a complete compile-and-link.
Peter Maydell [Tue, 8 Apr 2014 15:51:11 +0000 (16:51 +0100)]
hw/pci-host/prep: Don't reverse IO accesses on bigendian hosts
The raven_io_read() and raven_io_write() functions pass and
return values in little-endian format (since the IO op struct
is marked DEVICE_LITTLE_ENDIAN); however they were storing the
values in the buffer to pass to address_space_read/write()
in host-endian order, which meant that on big-endian hosts
the values were inadvertently reversed. Use the *_le_p()
accessors instead so that we are consistent regardless of
host endianness.
Strictly speaking the byte order of the buffer for
address_space_rw() is target byte order (which for PPC
will be BE) but it doesn't actually matter as long as we
are consistent about the marking on the IO op struct and
which stl_*_p().
This bug was probably introduced due to confusion caused by
the two different versions of ldl_p() and friends:
bswap.h defines versions meaning "host endianness access"
cpu-all.h defines versions meaning "target endianness access"
As a target-independent source file prep.c gets the bswap.h
versions; the very similar looking code in ioport.c is
compiled per-target and gets the cpu-all.h versions.
Peter Maydell [Tue, 8 Apr 2014 12:59:28 +0000 (13:59 +0100)]
Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging
acpi bug fix
Here is a single last minute fix for 2.0
This changes the HID of the container used to claim
resources for CPU hotplug.
As a result, windows XP SP3 no longer brings up
an annoying "found new hardware" wizard on boot.
Signed-off-by: Michael S. Tsirkin <[email protected]>
# gpg: Signature made Tue 08 Apr 2014 13:23:30 BST using RSA key ID D28D5469
# gpg: Good signature from "Michael S. Tsirkin <[email protected]>"
# gpg: aka "Michael S. Tsirkin <[email protected]>"
* remotes/mst/tags/for_upstream:
dsdt: tweak ACPI ID for hotplug resource device
ACPI0004 seems too new:
Windows XP complains about an unrecognized device.
This is a regression since 1.7.
Use PNP0A06 instead - Generic Container Device.
gtk: Implement grab-on-click behavior in relative mode
This patch changes the behavior in the relative mode to be compatible
with other UIs, namely, grabbing the input at the first left click.
It improves the usability a lot; otherwise you have to press ctl-alt-G
or select from menu at each time you want to move the pointer. Also,
the input grab is cleared when the current mode is switched to the
absolute mode.
The automatic reset of the implicit grabbing is needed since the
switching to the absolute mode happens always after the click even on
Gtk. That is, we cannot check whether the absolute mode is already
available at the first click time even though it should have been
switched in X11 input driver side.
Peter Maydell [Tue, 8 Apr 2014 09:58:31 +0000 (10:58 +0100)]
Merge remote-tracking branch 'remotes/agraf/tags/signed-ppc-for-upstream' into staging
Patch queue for ppc - 2014-04-08
This is the final queue for 2.0! It fixes a lot of bugs people have
seen during testing:
- Fix e500 SMP
- Fix book3s_64 DEC
- Fix VSX (new feature in 2.0) for LE hosts
- Fix PR KVM on top of pHyp (SLOF update)
# gpg: Signature made Tue 08 Apr 2014 10:24:18 BST using RSA key ID 03FEDC60
# gpg: Can't check signature: public key not found
* remotes/agraf/tags/signed-ppc-for-upstream:
PPC: Add l1 cache sizes for 970 and above systems
ppce500_spin: Initialize struct properly
PPC: Only enter MSR_POW when no interrupts pending
PPC: Clean up DECR implementation
target-ppc: Correct VSX Integer to FP Conversion
target-ppc: Correct VSX FP to Integer Conversion
target-ppc: Correct VSX FP to FP Conversions
target-ppc: Correct VSX Scalar Compares
target-ppc: Correct Simple VSR LE Host Inversions
target-ppc: Correct LE Host Inversion of Lower VSRs
target-ppc: Define Endian-Correct Accessors for VSR Field Access
target-ppc: Bug: VSX Convert to Integer Should Truncate
softfloat: Introduce float32_to_uint64_round_to_zero
pseries: Update SLOF firmware image to qemu-slof-20140404
PPC: E500: Set PIR default reset value rather than SPR value
Alexander Graf [Sat, 5 Apr 2014 23:32:06 +0000 (01:32 +0200)]
PPC: Clean up DECR implementation
There are 3 different variants of the decrementor for BookE and BookS.
The BookE variant sets TSR[DIS] to 1 when the DEC value becomes 1 or 0. TSR[DIS]
is then the indicator whether the decrementor interrupt line is asserted or not.
The old BookS variant treats DEC as an edge interrupt that gets triggered when
the DEC value's top bit turns 1 from 0.
The new BookS variant maintains the assertion bit inside DEC itself. Whenever
the DEC value becomes negative (top bit set) the DEC interrupt line is asserted.
So far we implemented mostly the old BookS variant. Let's do them all properly.
This fixes booting pseries ppc64 guest images in TCG mode for me.
Tom Musta [Mon, 31 Mar 2014 21:04:03 +0000 (16:04 -0500)]
target-ppc: Correct VSX Integer to FP Conversion
This patch corrects the VSX integer to floating point conversion instructions
by using the endian correct accessors. The auxiliary "j" index used by the
existing macros is now obsolete and is removed. The JOFFSET preprocessor
macro is also obsolete and removed.
Tom Musta [Mon, 31 Mar 2014 21:04:02 +0000 (16:04 -0500)]
target-ppc: Correct VSX FP to Integer Conversion
This patch corrects the VSX floating point to integer conversion
instructions by using the endian correct accessors. The auxiliary
"j" index used by the existing macros is now obsolete and is removed.
Tom Musta [Mon, 31 Mar 2014 21:04:01 +0000 (16:04 -0500)]
target-ppc: Correct VSX FP to FP Conversions
This change corrects the VSX double precision to single precision and
single precision to double precisions conversion routines. The endian
correct accessors are now used. The auxiliary "j" index is no longer
necessary and is eliminated.
Tom Musta [Mon, 31 Mar 2014 21:03:59 +0000 (16:03 -0500)]
target-ppc: Correct Simple VSR LE Host Inversions
A common pattern in the VSX helper code macros is the use of "x.fld[i]" where
"x" is a VSR and "fld" is an argument to a macro ("f64" or "f32" is passed).
This is not always correct on LE hosts.
This change addresses all instances of this pattern to be "x.fld" where "fld" is:
- "VsrD(0)" for scalar instructions accessing 64-bit numbers
- "VsrD(i)" for vector instructions accessing 64-bit numbers
- "VsrW(i)" for vector instructions accessing 32-bit numbers
Note that there are no instances of this pattern where a scalar instruction
accesses a 32-bit number.
Note also that it would be correct to use "VsrD(i)" for scalar instructions since
the loop index is only ever "0". I have choosen to use "VsrD(0)" instead ... it
seems a little clearer.
Tom Musta [Mon, 31 Mar 2014 21:03:58 +0000 (16:03 -0500)]
target-ppc: Correct LE Host Inversion of Lower VSRs
This change properly orders the doublewords of the VSRs 0-31. Because these
registers are constructed from separate doublewords, they must be inverted
on Little Endian hosts. The inversion is performed both when the VSR is read
and when it is written.
Tom Musta [Mon, 31 Mar 2014 21:03:57 +0000 (16:03 -0500)]
target-ppc: Define Endian-Correct Accessors for VSR Field Access
This change defines accessors for VSR doubleword and word fields that
are correct from a host Endian perspective. This allows code to
use the Power ISA indexing numbers in code.
For example, the xscvdpsxws instruction has a target VSR that looks
like this:
Tom Musta [Mon, 31 Mar 2014 21:03:56 +0000 (16:03 -0500)]
target-ppc: Bug: VSX Convert to Integer Should Truncate
The various VSX Convert to Integer instructions should truncate the
floating point number to an integer value, which is equivalent to
a round-to-zero rounding mode. The existing VSX floating point to
integer conversion helpers are erroneously using the rounding mode set
int the PowerPC Floating Point Status and Control Register (FPSCR).
This change corrects this defect by using the appropriate
float*_to_*_round_to_zero() routines fro the softfloat library.
This change adds the float32_to_uint64_round_to_zero function to the softfloat
library. This function fills out the complement of float32 to INT round-to-zero
conversion rountines, where INT is {int32_t, uint32_t, int64_t, uint64_t}.
This contribution can be licensed under either the softfloat-2a or -2b
license.
pseries: Update SLOF firmware image to qemu-slof-20140404
The change log is:
> Isolate sc 1 detection logic
> build: auto-detect ppc64 architecture
> cas: increase hcall buffer size to accomodate 256 cpus
> usb: change device tree naming
> usb-core: adjust port numbers in set_address
> virtio-scsi: correct srplun comment
> Fix kernel loading
> Workaround to make grub2 assign server ip from dhcp ack packet only
> ELF: Enter LE binary in LE mode
> ELF loading should fail for virt != phys
Alexander Graf [Thu, 3 Apr 2014 18:45:27 +0000 (20:45 +0200)]
PPC: E500: Set PIR default reset value rather than SPR value
We now reset SPRs to their reset values on CPU reset. So if we want
to have an SPR persistently changed, we need to change its default
reset value rather than the value itself manually.
Do this for SPR_BOOKE_PIR, fixing e500v2 SMP boot.
Tomoki Sekiyama [Wed, 26 Mar 2014 18:28:51 +0000 (14:28 -0400)]
vss-win32: Fix build with mingw64-headers-3.1.0
In mingw64-headers-3.1.0, definition of _com_issue_error() is added, which
conflicts with definition in install.cpp. This adds version checking for
mingw headers to disable the definition when the headers>=3.1 is used.
Tomoki Sekiyama [Wed, 26 Mar 2014 18:28:45 +0000 (14:28 -0400)]
Makefile: add qga-vss-dll-obj-y to nested variables
The build rule for qga/vss-win32/qga-vss.dll is broken by commit ba1183da9a10b94611cad88c44a5c6df005f9b55, because it misses
qga-vss-dll-obj-y in the list of nested variables.
This fixes build of qga-vss.dll by adding qga-vss-dll-obj-y to the list.
Michael Tokarev [Sat, 5 Apr 2014 14:25:46 +0000 (18:25 +0400)]
Makefile: remove bashism
When installing modules (when --enable-modules is specified for
./configure), Makefile uses the following construct to replace all
slashes with dashes in module name:
${s//\//-}
This is a bash-specific substitution mechanism. POSIX does not
have it, and some operating systems (for example Debian) does not
implement this construct in default shell (for example dash).
Use more traditional way to perform the substitution: use `tr' tool.
Peter Maydell [Mon, 7 Apr 2014 11:27:10 +0000 (12:27 +0100)]
Merge remote-tracking branch 'remotes/kraxel/tags/pull-gtk-4' into staging
gtk: pointer fixes from Takashi Iwai.
# gpg: Signature made Mon 07 Apr 2014 09:51:52 BST using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <[email protected]>"
# gpg: aka "Gerd Hoffmann <[email protected]>"
# gpg: aka "Gerd Hoffmann (private) <[email protected]>"
* remotes/kraxel/tags/pull-gtk-4:
ui: Update MAINTAINERS entry.
gtk: Remember the last grabbed pointer position
gtk: Fix the relative pointer tracking mode
gtk: Use gtk generic event signal instead of motion-notify-event
With Amazon eating Anthonys time status "Maintained" certainly isn't
true any more. Update entry accordingly.
Also add myself, so scripts/get_maintainer.pl will Cc: me, to reduce
the chance ui patches fall through the cracks on our pretty loaded
qemu-devel mailing list.
It's pretty annoying that the pointer reappears at a random place once
after grabbing and ungrabbing the input. Better to restore to the
original position where the pointer was grabbed.
The relative pointer tracking mode was still buggy even after the
previous fix of the motion-notify-event since the events are filtered
out when the pointer moves outside the drawing window due to the
boundary check for the absolute mode.
This patch fixes the issue by moving the unnecessary boundary check
into the if block of absolute mode, and keep the coordinate in the
relative mode even if it's outside the drawing area. But this makes
the coordinate (last_x, last_y) possibly pointing to (-1,-1),
introduce a new flag to indicate the last coordinate has been
updated.
gtk: Use gtk generic event signal instead of motion-notify-event
The GDK motion-notify-event isn't generated when the pointer goes out
of the target window even if the pointer is grabbed, which essentially
means to lose the pointer tracking in gtk-ui.
Meanwhile the generic "event" signal is sent when the pointer is
grabbed, so we can use this and pick the motion notify events manually
there instead.
Paolo Bonzini [Wed, 2 Apr 2014 15:33:02 +0000 (17:33 +0200)]
target-i386: reorder fields in cpu/msr_hyperv_hypercall subsection
The subsection already exists in one well-known enterprise Linux
distribution, but for some strange reason the fields were swapped
when forward-porting the patch to upstream.
Limit headaches for said enterprise Linux distributor when the
time will come to rebase their version of QEMU.
Peter Maydell [Fri, 4 Apr 2014 23:18:19 +0000 (00:18 +0100)]
Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging
Block patches for 2.0.0
# gpg: Signature made Fri 04 Apr 2014 20:25:08 BST using RSA key ID C88F2FD6
# gpg: Good signature from "Kevin Wolf <[email protected]>"
* remotes/kevin/tags/for-upstream:
dataplane: replace iothread object_add() with embedded instance
iothread: make IOThread struct definition public
dma-helpers: Initialize DMAAIOCB in_cancel flag
block: Check bdrv_getlength() return value in bdrv_append_temp_snapshot()
block: Fix snapshot=on for protocol parsed from filename
qemu-iotests: Remove CR line endings in reference output
block: Don't parse 'filename' option
qcow2: Put cache reference in error case
qcow2: Flush metadata during read-only reopen
iscsi: Don't set error if already set in iscsi_do_inquiry
Stefan Hajnoczi [Thu, 20 Mar 2014 14:06:32 +0000 (15:06 +0100)]
dataplane: replace iothread object_add() with embedded instance
Before IOThread was its own object, each virtio-blk device would create
its own internal thread. We need to preserve this behavior for
backwards compatibility when users do not specify -device
virtio-blk-pci,iothread=<id>.
This patch changes how the internal IOThread object is created.
Previously we used the monitor object_add() function, which is really a
layering violation. The problem is that this needs to assign a name but
we don't have a name for this internal object.
Generating names for internal objects is a pain but even worse is that
they may collide with user-defined names.
Paolo Bonzini <[email protected]> suggested that the internal IOThread
object should not be named. This way the conflict cannot happen and we
no longer need object_add().
One gotcha is that internal IOThread objects will not be listed by the
query-iothreads command since they are not named. This is okay though
because query-iothreads is new and the internal IOThread is just for
backwards compatibility. New users should explicitly define IOThread
objects.
Peter Maydell [Fri, 28 Mar 2014 14:22:49 +0000 (14:22 +0000)]
dma-helpers: Initialize DMAAIOCB in_cancel flag
Initialize the dbs->in_cancel flag in dma_bdrv_io(), since qemu_aio_get()
does not return zero-initialized memory. Spotted by the clang sanitizer
(which complained when the value loaded in dma_complete() was not valid
for a bool type); this might have resulted in leaking the AIO block.
Kevin Wolf [Thu, 3 Apr 2014 10:09:34 +0000 (12:09 +0200)]
block: Fix snapshot=on for protocol parsed from filename
Since commit 9fd3171a, BDRV_O_SNAPSHOT uses an option QDict to specify
the originally requested image as the backing file of the newly created
temporary snapshot. This means that the filename is stored in
"file.filename", which is an option that is not parsed for protocol
names. Therefore things like -drive file=nbd:localhost:10809 were
broken because it looked for a local file with the literal name
'nbd:localhost:10809'.
This patch changes the way BDRV_O_SNAPSHOT works once again. We now open
the originally requested image as normal, and then do a similar
operation as for live snapshots to put the temporary snapshot on top.
This way, both driver specific options and parsed filenames work.
As a nice side effect, this results in code movement to factor
bdrv_append_temp_snapshot() out. This is a good preparation for moving
its call to drive_init() and friends eventually.
Peter Maydell [Fri, 4 Apr 2014 16:42:56 +0000 (17:42 +0100)]
cpu-exec: Unlock tb_lock if we longjmp out of code generation
If the guest attempts to execute from unreadable memory, this will
cause us to longjmp back to the main loop from inside the
target frontend decoder. For linux-user mode, this means we will
still hold the tb_ctx.tb_lock, and will deadlock when we try to
start executing code again. Unlock the lock in the return-from-longjmp
code path to avoid this.
page_check_range: don't bail out early after unprotecting page
When checking a page range, if we found that a page was
made read-only by QEMU because it contained translated code,
we were incorrectly returning immediately after unprotecting
that page, rather than continuing to check the entire range,
so we might fail to unprotect pages later in the range, or
might incorrectly return a "success" result even if later
pages were not writable.
In particular, this could cause segfaults in a case where
signals are delivered back to back on a target architecture
which uses trampoline code in the stack frame (as AArch64
currently does). The second signal causes a segfault because
the frame cannot be written to (it was protected because
we translated and executed the restorer trampoline, and the
unprotect logic did not unprotect the whole range).
Peter Maydell [Fri, 4 Apr 2014 16:42:34 +0000 (17:42 +0100)]
hw/arm/vexpress, hw/arm/highbank: Don't insist that CPU has reset-cbar property
For the machine models which can have a Cortex-A15 CPU (vexpress-a15 and
midway), silently continue if the CPU object has no reset-cbar property
rather than failing. This allows these boards to be used under KVM with
the "-cpu host" option, since the 'host' CPU object has no reset-cbar
property.
Kevin Wolf [Thu, 3 Apr 2014 10:48:38 +0000 (12:48 +0200)]
qemu-iotests: Remove CR line endings in reference output
qemu doesn't print these CRs any more. The test still didn't fail
because the output comparison ignores line endings, but the change turns
up each time when you want to update the output.
Kevin Wolf [Thu, 3 Apr 2014 10:45:51 +0000 (12:45 +0200)]
block: Don't parse 'filename' option
When using the QDict option 'filename', it is supposed to be interpreted
literally. The code did correctly avoid guessing the protocol from any
string before the first colon, but it still called bdrv_parse_filename()
which would, for example, incorrectly remove a 'file:' prefix in the
raw-posix driver.
Kevin Wolf [Sat, 8 Feb 2014 16:44:59 +0000 (17:44 +0100)]
qcow2: Put cache reference in error case
When qcow2_get_cluster_offset() sees a zero cluster in a version 2
image, it (rightfully) returns an error. But in doing so it shouldn't
leak an L2 table cache reference.
Kevin Wolf [Thu, 3 Apr 2014 11:47:50 +0000 (13:47 +0200)]
qcow2: Flush metadata during read-only reopen
If lazy refcounts are enabled for a backing file, committing to this
backing file may leave it in a dirty state even if the commit succeeds.
The reason is that the bdrv_flush() call in bdrv_commit() doesn't flush
refcount updates with lazy refcounts enabled, and qcow2_reopen_prepare()
doesn't take care to flush metadata.
In order to fix this, this patch also fixes qcow2_mark_clean(), which
contains another ineffective bdrv_flush() call beause lazy refcounts are
disabled only afterwards. All existing callers of qcow2_mark_clean()
either don't modify refcounts or already flush manually, so that this
fixes only a latent, but not yet actually triggerable bug.
Another instance of the same problem is live snapshots. Again, a real
corruption is prevented by an explicit flush for non-read-only images in
external_snapshot_prepare(), but images using lazy refcounts stay dirty.