Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- qcow2: Support for external data files
- qcow2: Default to 4KB for the qcow2 cache entry size
- Ap

Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Block layer patches:

- qcow2: Support for external data files
- qcow2: Default to 4KB for the qcow2 cache entry size
- Apply block driver whitelist for -drive format=help
- Several qemu-iotests improvements

# gpg: Signature made Fri 08 Mar 2019 12:54:27 GMT
# gpg: using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <kwolf@redhat.com>" [full]
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74 56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream: (33 commits)
qcow2 spec: Describe string header extensions
qemu-iotests: Add dependency to qemu-nbd tool
ahci-test: Add dependency to qemu-img tool
qemu-iotests: amend with external data file
qemu-iotests: General tests for qcow2 with external data file
qemu-iotests: Preallocation with external data file
qcow2: Implement data-file-raw create option
qcow2: Store data file name in the image
qcow2: Creating images with external data file
qcow2: Add basic data-file infrastructure
qcow2: Support external data file in qemu-img check
qcow2: Return error for snapshot operation with data file
qcow2: External file I/O
qcow2: Prepare qcow2_co_block_status() for data file
qcow2: Return 0/-errno in qcow2_alloc_compressed_cluster_offset()
qcow2: Don't assume 0 is an invalid cluster offset
qcow2: Prepare count_contiguous_clusters() for external data file
qcow2: Prepare qcow2_get_cluster_type() for external data file
qcow2: Pass bs to qcow2_get_cluster_type()
qcow2: Basic definitions for external data files
...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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qemu-iotests: Preallocation with external data file

Test that preallocating metadata results in a somewhat larger qcow2
file, but preallocating data only affects the disk usage of the data
file and

qemu-iotests: Preallocation with external data file

Test that preallocating metadata results in a somewhat larger qcow2
file, but preallocating data only affects the disk usage of the data
file and the qcow2 file stays small.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

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qemu-iotests: Test qcow2 preallocation modes

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>