Improve convert and dd commands

Update to

v1: https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg05699.html
v2: https://lists.gnu.org/archive/html/qemu-devel/2017-02/msg00728.html
v3: https://lists.gnu.org/archive/html/qemu-devel/2017-02/msg04391.html
v4: https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg02153.html
v5: https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg04109.html
v6: https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg00215.html
v7: https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg00242.html
v8: https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg02028.html
v9: https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg03504.html

This series is in response to Max pointing out that you cannot use 'convert' for an encrypted target image.

The 'convert' and 'dd' commands need to first create the image and then open it. The bdrv_create() method takes a set of options for creating the image, which let us provide a key-secret for the encryption key. When the commands then open the new image, they don't provide any options, so the image is unable to be opened due to lack of encryption key. It is also not possible to use the --image-opts argument to provide structured options in the target image name - it must be a plain filename to satisfy the bdrv_create() API contract.

This series addresses these problems to some extent

- Adds a new --target-image-opts flag which is used to say that the target filename is using structured options. It is *only* permitted to use this when -n is also set. ie the target image must be pre-created so convert/dd don't need to run bdrv_create().

- When --target-image-opts is not used, add special case code that identifies options passed to bdrv_create() named "*key-secret" and adds them to the options used to open the new image

In future it is desirable to make --target-image-opts work even when -n is *not* given. This requires considerable work to create a new bdrv_create() API impl.

The first patch fixes a bug in the 'dd' command while the second adds support for the missing '--object' arg to 'dd', allowing it to reference secrets when opening files. The last two patches implement the new features described above for the 'convert' command.

Changed in v10:

- Fixed crash in qemu-img when locking flag is set, without fmt being set (seen when running iotest 153).

Changed in v9:

- Rebased against Kevin's "block" branch with Fam's patch "qemu-img: Fix documentation of convert" applied first

Changed in v8:

- Readd accidentally dropped check for compression (Max)
- Fix indentation of variable declaration (Max)
- Fix goto jump target (Max)

Changed in v7:

- Drop the (accidentally included) revert patch (Eric)

Changed in v6:

- Fix misc typos (Fam)
- Resolve messy conflicts wrt max/block-next (Max)

Changed in v5:

- Fix return value (Max)
- Misc doc changes (Max)
- Use error_abort (Max)

Changed in v4:

- Refactor img_open_new_file in terms of img_open_file (Kevin)

Changed in v3:

- Drop all patches affecting the 'dd' command except for the clear bug fix and the --object support. They can be re-considered once dd is rewritten to run ontop of convert.
- Use consistent return/goto style in dd command (Max)
- Fix error reporting when using compressed image and skip-create (Max)
- Unconditionally create QDict when open files (Max)

Changed in v2:

- Replace dd -n flag with support for conv=nocreat,notrunc
- Misc typos (Eric, Fam)

Daniel P. Berrange (4):
qemu-img: add support for --object with 'dd' command
qemu-img: fix --image-opts usage with dd command
qemu-img: introduce --target-image-opts for 'convert' command
qemu-img: copy *key-secret opts when opening newly created files

 qemu-img-cmds.hx |   4 +-
 qemu-img.c       | 147 +++++++++++++++++++++++++++++++++++++++++++------------
 qemu-img.texi    |  12 ++++-
 3 files changed, 128 insertions(+), 35 deletions(-)

2.9.3