Once there, make  count field to always be accessed with atomic
operations.  To make blocking operations, we need to know that the
thread is running, so create a bool to indicate that.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

--

Once here, s/terminate_multifd_*-threads/multifd_*_terminate_threads/
This is consistente with every other function

Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

Signed-off-by: NJuan Quintela <quintela@redhat.com>

No need to write it to a file.  Just need a proper firmware O:-)
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NLaurent Vivier <lvivier@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>

Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NPeter Xu <peterx@redhat.com>

Fix the bug introduced by da3f56cb (migration: remove
ram_save_compressed_page()), It should be 'return' rather than
'res'

Sorry for this stupid mistake :(
Signed-off-by: NXiao Guangrong <xiaoguangrong@tencent.com>
Message-Id: <20180428081045.8878-1-xiaoguangrong@tencent.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

Block layer patches:

- Switch AIO/callback based block drivers to a byte-based interface
- Block jobs: Expose error string via query-block-jobs
- Block job cleanups and fixes
- hmp: Allow using a qdev id in block_set_io_throttle

# gpg: Signature made Tue 15 May 2018 16:33:10 BST
# gpg:                using RSA key 7F09B272C88F2FD6
# 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: (37 commits)
  iotests: Add test for -U/force-share conflicts
  qemu-img: Use only string options in img_open_opts
  qemu-io: Use purely string blockdev options
  block: Document BDRV_REQ_WRITE_UNCHANGED support
  qemu-img: Check post-truncation size
  iotests: Add test for COR across nodes
  iotests: Copy 197 for COR filter driver
  iotests: Clean up wrap image in 197
  block: Support BDRV_REQ_WRITE_UNCHANGED in filters
  block/quorum: Support BDRV_REQ_WRITE_UNCHANGED
  block: Set BDRV_REQ_WRITE_UNCHANGED for COR writes
  block: Add BDRV_REQ_WRITE_UNCHANGED flag
  block: BLK_PERM_WRITE includes ..._UNCHANGED
  block: Add COR filter driver
  iotests: Skip 181 and 201 without userfaultfd
  iotests: Add failure matching to common.qemu
  docs: Document the new default sizes of the qcow2 caches
  qcow2: Give the refcount cache the minimum possible size by default
  specs/qcow2: Clarify that compressed clusters have the COPIED bit reset
  Fix error message about compressed clusters with OFLAG_COPIED
  ...
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

- Copy-on-read block driver
- The qcow2 default refcount cache size has been decreased
- Various bug fixes

# gpg: Signature made Tue May 15 16:18:25 2018 CEST
# gpg:                using RSA key F407DB0061D5CF40
# 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-2018-05-15: (21 commits)
  iotests: Add test for -U/force-share conflicts
  qemu-img: Use only string options in img_open_opts
  qemu-io: Use purely string blockdev options
  block: Document BDRV_REQ_WRITE_UNCHANGED support
  qemu-img: Check post-truncation size
  iotests: Add test for COR across nodes
  iotests: Copy 197 for COR filter driver
  iotests: Clean up wrap image in 197
  block: Support BDRV_REQ_WRITE_UNCHANGED in filters
  block/quorum: Support BDRV_REQ_WRITE_UNCHANGED
  block: Set BDRV_REQ_WRITE_UNCHANGED for COR writes
  block: Add BDRV_REQ_WRITE_UNCHANGED flag
  block: BLK_PERM_WRITE includes ..._UNCHANGED
  block: Add COR filter driver
  iotests: Skip 181 and 201 without userfaultfd
  iotests: Add failure matching to common.qemu
  docs: Document the new default sizes of the qcow2 caches
  qcow2: Give the refcount cache the minimum possible size by default
  specs/qcow2: Clarify that compressed clusters have the COPIED bit reset
  Fix error message about compressed clusters with OFLAG_COPIED
  ...
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180502202051.15493-4-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

img_open_opts() takes a QemuOpts and converts them to a QDict, so all
values therein are strings.  Then it may try to call qdict_get_bool(),
however, which will fail with a segmentation fault every time:

$ ./qemu-img info -U --image-opts \
    driver=file,filename=/dev/null,force-share=off
[1]    27869 segmentation fault (core dumped)  ./qemu-img info -U
--image-opts driver=file,filename=/dev/null,force-share=off

Fix this by using qdict_get_str() and comparing the value as a string.
Also, when adding a force-share value to the QDict, add it as a string
so it fits the rest of the dict.

Cc: qemu-stable@nongnu.org
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180502202051.15493-3-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Currently, qemu-io only uses string-valued blockdev options (as all are
converted directly from QemuOpts) -- with one exception: -U adds the
force-share option as a boolean.  This in itself is already a bit
questionable, but a real issue is that it also assumes the value already
existing in the options QDict would be a boolean, which is wrong.

That has the following effect:

$ ./qemu-io -r -U --image-opts \
    driver=file,filename=/dev/null,force-share=off
[1]    15200 segmentation fault (core dumped)  ./qemu-io -r -U
--image-opts driver=file,filename=/dev/null,force-share=off

Since @opts is converted from QemuOpts, the value must be a string, and
we have to compare it as such.  Consequently, it makes sense to also set
it as a string instead of a boolean.

Cc: qemu-stable@nongnu.org
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180502202051.15493-2-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Add BDRV_REQ_WRITE_UNCHANGED to the list of flags honored during pwrite
and pwrite_zeroes, and also add a note on when you absolutely need to
support it.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180502140359.18222-1-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Some block drivers (iscsi and file-posix when dealing with device files)
do not actually support truncation, even though they provide a
.bdrv_truncate() method and will happily return success when providing a
new size that does not exceed the current size.  This is because these
drivers expect the user to resize the image outside of qemu and then
provide qemu with that information through the block_resize command
(compare cb1b83e7).

Of course, anyone using qemu-img resize will find that behavior useless.
So we should check the actual size of the image after the supposedly
successful truncation took place, emit an error if nothing changed and
emit a warning if the target size was not met.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1523065Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180421163957.29872-1-mreitz@redhat.com
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

COR across nodes (that is, you have some filter node between the
actually COR target and the node that performs the COR) cannot reliably
work together with the permission system when there is no explicit COR
node that can request the WRITE_UNCHANGED permission for its child.
This is because COR (currently) sneaks its requests by the usual
permission checks, so it can work without a WRITE* permission; but if
there is a filter node in between, that will re-issue the request, which
then passes through the usual check -- and if nobody has requested a
WRITE_UNCHANGED permission, that check will fail.

There is no real direct fix apart from hoping that there is someone who
has requested that permission; in case of just the qemu-io HMP command
(and no guest device), however, that is not the case.  The real real fix
is to implement the copy-on-read flag through an implicitly added COR
node.  Such a node can request the necessary permissions as shown in
this test.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180421132929.21610-10-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

iotest 197 tests copy-on-read using the (now old) copy-on-read flag.
Copy it to 215 and modify it to use the COR filter driver instead.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180421132929.21610-9-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-8-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Update the rest of the filter drivers to support
BDRV_REQ_WRITE_UNCHANGED.  They already forward write request flags to
their children, so we just have to announce support for it.

This patch does not cover the replication driver because that currently
does not support flags at all, and because it just grabs the WRITE
permission for its children when it can, so we should be fine just
submitting the incoming WRITE_UNCHANGED requests as normal writes.

It also does not cover format drivers for similar reasons.  They all use
bdrv_format_default_perms() as their .bdrv_child_perm() implementation
so they just always grab the WRITE permission for their file children
whenever possible.  In addition, it often would be difficult to
ascertain whether incoming unchanging writes end up as unchanging writes
in their files.  So we just leave them as normal potentially changing
writes.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-7-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

We just need to forward it to quorum's children (except in case of a
rewrite because of corruption), but for that we first have to support
flags in child requests at all.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-6-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-5-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

This flag signifies that a write request will not change the visible
disk content.  With this flag set, it is sufficient to have the
BLK_PERM_WRITE_UNCHANGED permission instead of BLK_PERM_WRITE.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-4-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Currently we never actually check whether the WRITE_UNCHANGED
permission has been taken for unchanging writes.  But the one check that
is commented out checks both WRITE and WRITE_UNCHANGED; and considering
that WRITE_UNCHANGED is already documented as being weaker than WRITE,
we should probably explicitly document WRITE to include WRITE_UNCHANGED.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-3-mreitz@redhat.com
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

This adds a simple copy-on-read filter driver.  It relies on the already
existing COR functionality in the central block layer code, which may be
moved here once we no longer need it there.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180421132929.21610-2-mreitz@redhat.com
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

userfaultfd support depends on the host kernel, so it may not be
available.  If so, 181 and 201 should be skipped.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180406151731.4285-3-mreitz@redhat.com
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Currently, common.qemu only allows to match for results indicating
success.  The only way to fail is by provoking a timeout.  However,
sometimes we do have a defined failure output and can match for that,
which saves us from having to wait for the timeout in case of failure.
Because failure can sometimes just result in a _notrun in the test, it
is actually important to care about being able to fail quickly.

Also, sometimes we simply do not get any specific output in case of
success.  The only way to handle this currently would be to define an
error message as the string to look for, which means that actual success
results in a timeout.  This is really bad because it unnecessarily slows
down a succeeding test.

Therefore, this patch adds a new parameter $success_or_failure to
_timed_wait_for and _send_qemu_cmd.  Setting this to a non-empty string
makes both commands expect two match parameters: If the first matches,
the function succeeds.  If the second matches, the function fails.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180406151731.4285-2-mreitz@redhat.com
Signed-off-by: NMax Reitz <mreitz@redhat.com>

We have just reduced the refcount cache size to the minimum unless
the user explicitly requests a larger one, so we have to update the
documentation to reflect this change.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Message-id: c5f0bde23558dd9d33b21fffc76ac9953cc19c56.1523968389.git.berto@igalia.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

The L2 and refcount caches have default sizes that can be overridden
using the l2-cache-size and refcount-cache-size (an additional
parameter named cache-size sets the combined size of both caches).

Unless forced by one of the aforementioned parameters, QEMU will set
the unspecified sizes so that the L2 cache is 4 times larger than the
refcount cache.

This is based on the premise that the refcount metadata needs to be
only a fourth of the L2 metadata to cover the same amount of disk
space. This is incorrect for two reasons:

 a) The amount of disk covered by an L2 table depends solely on the
    cluster size, but in the case of a refcount block it depends on
    the cluster size *and* the width of each refcount entry.
    The 4/1 ratio is only valid with 16-bit entries (the default).

 b) When we talk about disk space and L2 tables we are talking about
    guest space (L2 tables map guest clusters to host clusters),
    whereas refcount blocks are used for host clusters (including
    L1/L2 tables and the refcount blocks themselves). On a fully
    populated (and uncompressed) qcow2 file, image size > virtual size
    so there are more refcount entries than L2 entries.

Problem (a) could be fixed by adjusting the algorithm to take into
account the refcount entry width. Problem (b) could be fixed by
increasing a bit the refcount cache size to account for the clusters
used for qcow2 metadata.

However this patch takes a completely different approach and instead
of keeping a ratio between both cache sizes it assigns as much as
possible to the L2 cache and the remainder to the refcount cache.

The reason is that L2 tables are used for every single I/O request
from the guest and the effect of increasing the cache is significant
and clearly measurable. Refcount blocks are however only used for
cluster allocation and internal snapshots and in practice are accessed
sequentially in most cases, so the effect of increasing the cache is
negligible (even when doing random writes from the guest).

So, make the refcount cache as small as possible unless the user
explicitly asks for a larger one.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Message-id: 9695182c2eb11b77cb319689a1ebaa4e7c9d6591.1523968389.git.berto@igalia.com
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Compressed clusters are not supposed to have the COPIED bit set, but
this is not made explicit in the specs, so let's document it.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Message-id: 74552e1d6e858d3159cb0c0e188e80bc9248e337.1523376013.git.berto@igalia.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Compressed clusters are not supposed to have the COPIED bit set.
"qemu-img check" detects that and prints an error message reporting
the number of the affected host cluster. This doesn't make much sense
because compressed clusters are not aligned to host clusters, so it
would be better to report the offset instead. Plus, the calculation is
wrong and it uses the raw L2 entry as if it was simply an offset.

This patch fixes the error message and reports the offset of the
compressed cluster.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Message-id: 0f687957feb72e80c740403191a47e607c2463fe.1523376013.git.berto@igalia.com
Signed-off-by: NMax Reitz <mreitz@redhat.com>

Commit abd3622c added a case to 122
regarding how the qcow2 driver handles an incorrect compressed data
length value.  This does not really fit into 122, as that file is
supposed to contain qemu-img convert test cases, which this case is not.
So this patch splits it off into its own file; maybe we will even get
more qcow2-only compression tests in the future.

Also, that test case does not work with refcount_bits=1, so mark that
option as unsupported.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180406164108.26118-1-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

The backup block job directly accesses the driver field in BlockJob. Add
a wrapper for getting it.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

This gets us rid of more direct accesses to BlockJob fields from the
job drivers.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

All block job drivers support .set_speed and all of them duplicate the
same code to implement it. Move that code to blockjob.c and remove the
now useless callback.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

Every block job has a RateLimit, and they all do the exact same thing
with it, so it should be common infrastructure. Move the struct field
for a start.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

Block job drivers are not expected to mess with the internals of the
BlockJob object, so provide wrapper functions for one of the cases where
they still do it: Updating the progress counter.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

Every job gets a non-NULL job->txn on creation, but it doesn't
necessarily keep it until it is decommissioned: Finalising a job removes
it from its transaction. Therefore, calling 'blockdev-job-finalize' a
second time on an already concluded job causes an assertion failure.

Remove job->txn from the assertion in block_job_finalize() to fix this.
block_job_do_finalize() still has the same assertion, but if a job is
already removed from its transaction, block_job_apply_verb() will
already error out before we run into that assertion.

Cc: qemu-stable@nongnu.org
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>

When we've reached the concluded state, we need to expose the error
state if applicable. Add the new field.

This should be sufficient for determining if a job completed
successfully or not after concluding; if we want to discriminate
based on how it failed more mechanically, we can always add an
explicit return code enumeration later.

I didn't bother to make it only show up if we are in the concluded
state; I don't think it's necessary.

Cc: qemu-stable@nongnu.org
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

The QMP version of this command can take a qdev ID since 7a9877a0,
but the HMP version is still using the deprecated block device name so
there's no way to refer to a block device added like this:

  -blockdev node-name=disk0,driver=qcow2,file.driver=file,file.filename=hd.qcow2
  -device virtio-blk-pci,id=virtio-blk-pci0,drive=disk0

This patch works around this problem by using the specified name as a
qdev ID if the block device name is not found.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

We have too many driver callback interfaces; simplify the mess
somewhat by merging the flags parameter of .bdrv_co_writev_flags()
into .bdrv_co_writev().  Note that as long as a driver doesn't set
.supported_write_flags, the flags argument will be 0 and behavior is
identical.  Also note that the public function bdrv_co_writev() still
lacks a flags argument; so the driver signature is thus intentionally
slightly different.  But that's not the end of the world, nor the first
time that the driver interface differs slightly from the public
interface.

Ideally, we should be rewriting all of these drivers to use modern
byte-based interfaces.  But that's a more invasive patch to write
and audit, compared to the simplification done here.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

We are gradually moving away from sector-based interfaces, towards
byte-based.  Now that all drivers with aio callbacks are using the
byte-based interfaces, we can remove the sector-based versions.
Signed-off-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

We are gradually moving away from sector-based interfaces, towards
byte-based.  Make the change for the last few sector-based callbacks
in the vxhs driver.

Note that the driver was already using byte-based calls for
performing actual I/O, so this just gets rid of a round trip
of scaling; however, as I don't know if VxHS is tolerant of
non-sector AIO operations, I went with the conservative approach
of adding .bdrv_refresh_limits to override the block layer
defaults back to the pre-patch value of 512.
Signed-off-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>