quorum: Create quorum.c, add QuorumSingleAIOCB and QuorumAIOCB.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Create BDRVQuorumState and BlkDriver and do init.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_aio_writev and its dependencies.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
blkverify: Extract qemu_iovec_clone() and qemu_iovec_compare() from blkverify.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_aio_readv.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum mechanism.

Use gnutls's SHA-256 to compare versions.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_getlength().

Check that every bs file returns the same length.
Otherwize, return -EIO to disable the quorum and
avoid length discrepancy.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_invalidate_cache().

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_co_get_block_status.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_co_flush().

Makes a vote to select error if any.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Implement recursive .bdrv_recurse_is_first_non_filter in quorum.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
qemu-io: Allow block option to be passed to qemu-io (usefull for quorum tests)

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add quorum_open() and quorum_close().

Example of command line:
-drive if=virtio,file.driver=quorum,\
file.children.0.file.filename=1.raw,\
file.children.0.node-name=1.raw,\
file.children.0.driver=raw,\
file.children.1.file.filename=2.raw,\
file.children.1.node-name=2.raw,\
file.children.1.driver=raw,\
file.children.2.file.filename=3.raw,\
file.children.2.node-name=3.raw,\
file.children.2.driver=raw,\
file.vote_threshold=2

file.blkverify=on with file.vote_threshold=2 and two files can be passed to
emulated blkverify.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
quorum: Add unit test.

Signed-off-by: Benoit Canet <benoit@irqsave.net>